John Perkins didn't wield a gun - he wasn't even a paid-up CIA agent - but he did have nefarious ways of making countries around the world bend to the will of the US. Until, he tells Gary Younge, his conscience got the better of him and he looked for other ways to change the world

On November 24 2002, Lucio Gutierrez swept to power in Ecuador's presidential election. It was a momentous victory for the populist, leftwing leader who had pledged support for the poor indigenous Indians in a country where 60% live in poverty.

The way John Perkins tells it, within a week Gutierrez had a visitor. "An economic hit man walked into his office and said, 'Congratulations, Mr President, I just want you to know that over here I've got a couple of hundred million dollars for you and your family if you cooperate with your Uncle Sam and our oil companies. And over here I have a man with a gun in his hand and a bullet with your name on it.'"

Within two months of his election, Gutierrez had apparently made his choice. Implementing a swingeing austerity programme that attacked the very livelihoods of the people who elected him, he raised fuel prices by more than 35% and froze public sector workers' salaries for a year.

"It's a particularly tough position to be in," admits Perkins. "If you're really conscientious, you're probably going to compromise. You're going to say, 'I've got to stay in office. I can do better than anyone else, but somehow I've got to appease these people.' And the whole time that economic hit man is in your office he's saying, 'Remember Noriega, remember Allende, remember Lumumba. Remember, remember, remember.' There's a long list of guys who did not go along and were either overthrown or assassinated ... They may say it more subtly, but the message is very clear."

Two years later, a huge popular uprising forced Gutierrez from office. Now an interim government awaits elections for a new leader. Within a few days of that election, says Perkins, another "economic hit man" will return with another ultimatum.

With his tales of hit men, assassinations and coups, Perkins, now 60, sounds as if he has just slipped off a grassy knoll and landed on the deck of his waterfront home in West Palm Beach, Florida. But for him this is no conspiracy theory. The hit men he refers to are not metaphorical. "I mean literally and physically they will walk into your office," he tells me. And he should know - for a decade, Perkins was one of them.

In 1972 Perkins went to see the then dictator of Panama, General Omar Torrijos. Torrijos was a nationalist who was eager to wrest control of the Panama Canal from the US. Perkins went in to read him the riot act and came out with what sounded like an agreement. Some years later, Torrijos started talking to the Japanese about building a larger, sea-level canal for Panama that would have undermined American influence and corporate interests in the area. One night in 1981 Torrijos died when his Twin Otter aircraft crashed under mysterious circumstances. Perkins is convinced he was killed by US interests who placed a bomb on the plane. Had he lived, Perkins writes in his book, Confessions Of An Economic Hit Man, "He would have served as a role model for a generation of leaders in the Americas, Africa and Asia - something the CIA, the NSA [National Security Agency] and the EHMs [economic hit men] could not allow."

Economic hit men resort to such heavy-handed tactics, says Perkins, only when all other means of leverage have failed. The rest of the time they would employ a mixture of bribery, sex, flattery, prostitution, distortion, extortion, abduction and invasion to get their own way. "Sex was a very common tool used by economic hit men," Perkins says. "It was not uncommon for us to seduce wives of oil company executives because that was a way of gaining information and learning things about their husbands."

If the threats of the economic hit men don't persuade, the "jackals" will come in to make good on them. The jackals, says Perkins, are the CIA-sanctioned heavy mob who foment coups and revolutions, murder, abduction and assassination. And when the jackals fail, as was the case in Iraq, then the military goes in.

Economic hit men, Perkins says, work entirely separately but completely in concert with the state. Perkins never once reported to a US government agency - but he is in little doubt that the US government always knew and approved of what he was doing. His task, he says, was to ensure that US business interests came out on top, regardless of who won an election, and that the American wealthy were further enriched, regardless of who was impoverished as a result.

In his role as an analyst for the international consulting firm Main, Perkins worked for what he calls the "corporatocracy" - global big business. His first task was to persuade foreign governments to take large loans for huge engineering and construction projects conducted by US companies such as Halliburton and Bechtel. To achieve this, Perkins produced reports that would vastly exaggerate the benefit such projects would bring to the nation's economic development, thereby making it vulnerable.

Then, he writes, "I would work to bankrupt the countries that received those loans so that they would be for ever beholden to their creditors, and so they would present easy targets when we needed favours, including military bases, UN votes, or access to oil and other natural resources."

For all of this, Perkins earned a substantial wage and through his 20s and 30s lived large on a lavish expense account. Based in Boston, his work took him to, among other places, Indonesia, Saudi Arabia, Ecuador, Iran, Colombia.

But misgivings that he harboured from the outset grew with his salary. At 36, Perkins was about to be made the youngest partner in Main's history - a promotion that would have made him a millionaire by the age of 40. Fearing the seductive lure of his new position, he decided he had to leave.

He says it was like having an angel and a devil sitting on each shoulder and calling him in different directions. "I had both these guys shouting at me and I could turn either way I wanted. I couldn't turn away from the good conscience. It kept whispering in my ear. But I could live according to the bad conscience because everybody around me was."

The devil kept waving his wallet, but gradually Perkins retreated. He quit Main in 1980, although for several years after he could not resist continuing to accept freelance consulting jobs.

His recruitment into the world of economic hit men sounds like a scene from a James Bond movie. The story began with him as a young man looking for information about Kuwait in a Boston library shortly after he had started working for Main. An attractive, older woman named Claudine, whom he had never seen before, sat opposite him and slid over a book with the precise information he was looking for and her business card. "I've been asked to help in your training," she said.

Perkins, who was married at the time, started an affair with Claudine, who simultaneously inveigled him into the world of economic hit men. "At the time I thought she really cared so deeply for me," says Perkins. "But, of course, now I see it was part of her job."

A few years earlier, he had sought deferment of going to fight in Vietnam by applying for a job at the National Security Agency. After several interviews and a day of psychological profiling, he was offered a job to train as a spy. He never took the job in the end, joining the peace corps instead, but he is convinced that the results of his NSA tests identified him as having the ideal insecurities to be inducted as an economic hit man. Raised by Calvinist parents in an environment as emotionally cold as a New England winter, his vulnerability was not difficult to find. Claudine was there to finish off the job. "She was amazingly effective at what she did and she learned from my NSA tests that I had the three big weaknesses of modern culture - that is, the weakness for money, power and sex - and she exploited all of them. In many respects, she appealed to all my fantasies. And she started by giving me the sexual fantasy."

Her induction speech was melodramatic and definitive. "You're not alone," she told him. "We're a rare breed in a dirty business. No one can know about your involvement - not even your wife. I'll be very frank with you, teach you all I can during the next weeks, then you'll have to choose. Your decision is final. Once you're in, you're in for life."

Claudine disappeared almost as mysteriously as she appeared, leaving Perkins to make his wildly extravagant forecasts designed to corrupt and bankrupt developing nations. He never needed Big Brother or Sister, or any more instructions, after that. He knew the template he had to work to and, so long as he fulfilled the task, everyone was happy and he was handsomely rewarded.

"I wasn't making bucketloads of money," he says. "For many of those years I was making a decent salary, but it certainly wasn't what lawyers were making. But I had phenomenal expense accounts. I was living like a king. I was travelling first class, best hotels, best food, women always there. I could throw money around, but my salary wasn't that great."

He was fully aware of the consequences of his actions. "I knew that building electric power plants probably would increase the gross national product in a country, even if not by as much as I was predicting, but I also knew that it wouldn't help the majority of poor people in these countries because they didn't even have a light bulb. It doesn't matter what the hell GNP does in these countries, because it's not going to help the poor people. So I knew the promise wasn't true."

But Perkins carried on anyway. His conscience piqued him, but with all the positive reinforcement around him, it couldn't quite stop him in his tracks. "There is a great line in the new Harry Potter movie where he says we can do the right thing or the easy thing. And I could do the easy thing for me because it was lucrative and enjoyable... I was being invited to speak at Harvard and other universities around the world on these subjects. I was being patted on the back by Robert McNamara, the president of the World Bank. I could convince myself that I was doing a good thing."

But morality would eventually trump venality. Damascene moments are rare in real life. David Brock, the former rightwing muckracker who made a career trashing the Clintons and Anita Hill, and later repented, wrote: "As a young zealot, I disciplined myself to ignore the soft tug of my own conscience and see only what I was supposed to see." And so it was with Perkins. But it was less of a blinding flash of light than an evolutionary process that would eventually turn him inside out - among other things, it sounds as though he just got bored and started growing up.

"I was burned out and I really wanted to start a new life," he says. "There had been a lot of women, but that had also cost me a marriage. I had found a new woman [his current wife] and I was very fond of her. And I was no longer going to live this life of travelling and big expense accounts. I was spending all this time in the office, deciding who gets raises and who sits in the window seat. I had become a top-level manager."

None the less, leaving was an "awful wrench" which left him in a daze. "I spent the next couple of weeks going down to the Quincy market in Boston and I would sit there on one of the benches reading Shakespeare. I was lost and didn't know what to do with myself."

He was rescued from his disorientation by a call from Main. A client had said they would sign up for some work only if he were leading the team. "I jumped and then, as I'm falling through midair thinking, 'Holy shit, what have I done?' a trampoline appears at the bottom and it's my own company again. That got me back into it again. Not exactly back in the game again. Not doing true EHM stuff. Not building empire. But back on the circuit working for corporate America."

It was during this period that Perkins founded an alternative energy company, Independent Power Systems. He remarried and moved to West Palm Beach, on Florida's hurricane-prone coastline, where he will interrupt his descriptions of coups and assassinations to catch the cry of an osprey. The energy project lasted 10 years, until 1990, when he sold his company and turned his attention to working with indigenous Indians throughout the Americas and on protecting the environment. He wrote five books, about indigenous cultures, shamanism, ecology and sustainability. The front page of his website reads, "John Perkins: Dedicated to changing the world."

By then he had become active, if not an activist, in antiglobalisation campaigns. He believes the protests that target the World Trade Organisation meetings and other showcase events of international capital, such as the demonstrations in Seattle in 1999, have a big impact. The guardians of global capital are powerful, he says, but they are also mortal and emotionally vulnerable.

"Corporate executives are fear-driven," he says. "They are afraid of many things. One of them is competition. One of them is not making enough money. One of them is not making as much money as somebody else. They're fearful. They're fearful of their board of directors, they're fearful of the next quarterly report, the bottom line, the price of stock. They live in constant fear of what tomorrow is going to bring. That includes being fearful of anything that is critical of their corporations or their way of life. So I think that demonstrations have a very powerful effect. The corporate executives are going to stand there and tell you that isn't true. But once again they are operating from a place of fear. Many of the corporate heads today grew up during the 1960s and the anti-Vietnam demonstrations, and they saw the power of that."

With the help of just one thinly veiled threat to keep his mouth shut, Perkins kept his vow of silence regarding the work of economic hit men until September 11 changed his mind.

"Back then, we never conceived of the US being attacked by someone who was living in a cave in Afghanistan," he says. "It was a lot more subtle a world in my time. We never worried about Che attacking us. We did worry about Cuba for a while, but that was the only thing we worried about. Now the stakes have changed radically... Bush is a great catalyst. I think he's pushing us to the edge."

It was then that Perkins wrote his memoir. The book was lionised by the alternative media on publication in the US and took off, despite being ignored by the mainstream media. "The New York Times and the other papers never mentioned the book except on their bestseller list," he says. Today, as he embarks on a book tour, he fears "a crazy man" could shoot him. "It's always a crazy man," he says. "John Kennedy was killed by a crazy man, Robert Kennedy was killed by a crazy man, Martin Luther King was killed by a crazy man. It's the crazy man who walks up to you after you've done a reading at a book store and sticks a gun in your gut and shoots you, and then he gets taken off some place and probably killed by somebody else or put in a straitjacket, and nobody really knows what really happened."

During the height of McCarthyism, President Eisenhower said that even when former communists confessed and turned on their former comrades, he could never quite trust them. They are "such liars and cheats", he told his attorney general, "that even when they apparently recant and later testify against someone else for his communist convictions, my first reaction is to believe that the accused person must be a patriot."

Perkins certainly has the zeal of a convert. "America has to change," he says. "The people of South America have sent a very strong message to America and to the world. Latin Americans have sent us a message. Middle Easterners have sent us a message. The voters of the US have to take the next step. It's up to us now. We must take this seriously. We're a nation of people that represents 5% of the world's population and consumes 25% of the world's resources. Simple mathematics will tell you that you can't sell that model to China or Africa or India. But we don't want to hear that. Because if you're one of the 5%, then you're leading a damned good life. Even the poorest among us are leading a much better life than the much less poor in the rest of the world."

At times it seems as though Perkins is using the knowledge he acquired as an economic hit man to assuage the wrongs he committed in the past. "We outlawed slavery back in the 1860s in the US, but we've taken it abroad. If you were to tell an executive at Monsanto or Nike or Wal-Mart that we use slave labour, they would say, 'No, we're paying them $2 a day. That's better than anyone else around them.' But the truth is we always paid slaves. Slaves on the plantations got free room and board. That's more than what most of these people in these other countries are getting; $2 a day probably doesn't buy their families room and board."

At other times it sounds as if Perkins is overcompensating. "Terrorism is a very poor choice of words," he says referring to the terror attacks of September 11. "I am in no way condoning the actions of a man like Osama bin Laden, who killed thousands of mostly innocent people. But, on the other hand, a lot of the people around the world who, in one way or another, support what we call terrorist movements, are basically very nationalistic people. They are fighting for their families, they're fighting for survival, they're fighting for their lives."

Mostly innocent?

"I have no doubt that there were people in the World Trade Centre who weren't innocent and who were part of this whole [economic] process," he says. "But they were probably a very small proportion of the people who were there. Most of the people killed there were innocent."

His analysis of how the "corporatocracy" works hand in glove with the American government to keep profits high and developing nations in check is entirely plausible. Much of it, particularly in Central and South America, is more or less a matter of public record. It's the details - crazy men, a seductress with a dossier on him - that are hard to swallow.

It wouldn't be the first time a powerful country such as the US has gone to extraordinary lengths to preserve its power. Tales of German and Italian nationals (to name but a few) being picked up on the street by the CIA and whisked to third countries where they are tortured, interrogated and then released months later without charge, beggar belief. But they are true. On the other hand, this wouldn't be the first time a good argument and compelling story has been embellished for effect. There is simply no way of knowing.

Softly spoken and articulate, Perkins does not talk like a braggart. You don't get the impression that he's looking for the dramatic and self-serving response to a question.

"The overall scheme is not a conspiracy," he says. "The corporatocracy is ourselves - we make it happen - which, of course, is why most of us find it difficult to stand up and oppose it. Conspiracy means doing something illegal by definition. The overall scheme is not. But within the overall schemes there are plenty of conspiracies going on."

Unlike most men of his age and generation, corporate, anticorporate or otherwise, Perkins listens and engages. In short, he is very believable; it's his story that is challenging. One wonders, for example, why a newly elected leader would need an economic hit man to come into his office and read him the riot act when capitalism delivers a pretty clear warning all by itself. When it was obvious that the leftwing Workers Party leader Luiz Inacio Lula da Silva would be elected president of Brazil in 2002, the invisible hand of the market picked him up by the scruff of the neck and slapped most of the socialism out of him. In the three months between his winning the vote and being sworn in, the currency had plummeted by 30%, $6bn in hot money had left the country and some agencies had given Brazil the highest debt risk ratings in the world.

"We are in government but not in power," said Lula's close aide, Dominican friar Frei Betto. "Power today is global power, the power of the big companies, the power of financial capital."

In short, there was nothing an economic hit man could tell Lula that the Financial Times hadn't said already. Lula had choices, argues Perkins, pointing to Hugo Chávez in Venezuela as an example of a South American leader from a smaller economy who weathered the storm. "Lula had a lot more control than he admits to having," he says. "The same thing happened to Lula that happened to Gutierrez - he was read the riot act. Today, they are a lot more crude."

And then there is the small question of why, given Claudine's warnings, he is alive to tell the tale?

"The word's out there," he says. "The book's sold 200,000 copies and is translated into 20 languages. What's getting rid of me going to do?"

· Confessions Of An Economic Hit Man, by John Perkins, will be published on February 7 by Ebury Press at £7.99. To order a copy with free UK p&p, call 0870 836 0875 (theguardian.com/bookshop).