"I think these large turnouts represent a widening distance between the political oligarchy in Washington and the democracy," he says. "Right now it's just a sentiment, a feeling. It's difficult to tell where it's all going because it has not reached a critical mass. But it's there in a much larger measure than either the Bush administration or the media would like you to believe."

Lapham, 61, is more qualified than most to say this because he is related to, if not a part of, the very oligarchy against which he now spends most of his time and energy railing - a Boston Brahmin whose roots spread to the west.

As mayor of San Francisco, his grandfather delivered the welcoming speech at the drafting of the UN charter in 1945. As US secretary of state for war, his great-great-grandfather led a botched military incursion into Canada in 1813. As a child, Lapham remembers passing a tray of puffed cheese to the Soviet commissar for foreign affairs, Vyacheslav Molotov, refraining from comment on Prince Faisal of Saudi Arabia's costume and chatting to the senior US adviser to the UN, John Foster Dulles, about the Bay Area fog.

At eight, he could draw the silhouette of every kind of plane in the US air force and every type of ship in the navy. "I have a tangential acquaintance with the great and the good. I was on the margins of that world during the Kennedy era," he says recalling both Jack and Teddy's birthday parties. "I get a sense of the inside and the outside."

It is a form of dual citizenship that strays into the personal as well as the political. He smokes, an outsider pursuit if ever there was one in New York right now, but his Zippo lighter bears the eagled crest of the United States. And his two packs a day are testament not just out to a habit but a conviction. When his friend, Ralph Nader, the consumer activist, offered him $21,000 (£13,000) worth of subscriptions to Harper's if he gave up, Lapham said: "I wouldn't want to sell out my principles or my belief in individual freedom for money."

The result is a mix between the epicurean instincts of Christopher Hitchens, the political perspective of Noam Chomsky and the social connections of Tina Brown. "Lewis is not your standard-brand leftie," says Neil Postman, chairman of the department of culture and communications at New York University and a friend of Lapham's. "He's an insider in that he is editor of a major literary journal so his complaints about American culture have a special weight that others would not have."

Lapham is under no illusions about how seriously his views are taken within the establishment. "They just ignore it. It's of no interest or consequence to them," he says with a smile. But his views about them are no less scathing. He recalls a lunch with a Soviet journalist who was also a KGB agent in a fashionable restaurant in Washington DC more than 20 years ago, surrounded by the political capital's beau monde. "He knew who was sleeping with whom and who was taking money from whom. And none of them knew who he was. It was just typical of the American plutocracy; the combination of perfect virtue and infinite wealth which means you don't have to know anything."

Like any self-respecting blue-blood, he attended a New England private school before moving on to Yale. "It was a very cloistered environment," he says, and with little to inspire him he got into Brecht and Camus. He left Yale for Cambridge, arriving in England in autumn 1956 and by 1960 was a correspondent at the UN for the International Herald Tribune.

His book draws on the full span of his experience. It is a brave piece of work on two fronts. First it frames the terrorist attack on the World Trade Centre within an international context which suggests that while US foreign policy is not culpable for the attack there is a connection between the two. "For what reason do we possess the largest store of weapons known to the history of mankind if not to kill as many people as we declare to be our enemies?" he asks in the introduction. "Why then should our enemies not kill us?"

American views on foreign policy have become increasingly nuanced at a time when such views still border on the heretical in the US - an unfortunate by-product, says Lapham, of American optimism and insularity. "We don't want to know about the past, only the future."

Second, it is brave because many of the essays in it were written before September 11. Ordinarily that would make most commentary on US politics and foreign policy appear dated.

He describes George Bush and Al Gore during the presidential elections as: "two ornamental sons of the American plutocracy bearing well-known brand names and with as little difference between them as Pepsi and Coke ... well enough schooled in the art of foraging for money to know where to stand and when to crawl."

It is a point that had more currency before President Bush put the world on notice that his presidency will be marked by permanent war. Would Gore be trying to bomb Baghdad now? "I don't know," concedes Lapham. He does not deny that there is a difference between Republicans and Democrats. "The Republicans are closer to being gangsters so they don't mind stealing the election if they have to do that, while the Democrats do have some conscience," he says.

To Lapham, September 11 did not represent a paradigm shift in either American or world politics but a continuum of it that makes a more long-term perspective vital. "I'm interested in the transformation of democracy into something more closely resembling a plutocracy. This has been happening steadily for the last 30 years. Ever since Nixon, nobody in the White House talks in a way that can be written down or even remembered."

Ronald Reagan exacerbated that trend, says Lapham, promoting the corporate at the expense of the state and extolling the individual over the collective. "The word 'public' used to be regarded as something good and common, while 'private' suggested selfishness and greed. But, gradually, public has become identified with slums, inefficiency and corruption and private means all that's good and beautiful."

The result, he believes, has been a full-scale degradation in American political culture. "It seems like politics has just been reduced to trivial entertainment. So long as we could buy an SUV or a condo in Florida, what the hell difference did it make who was running the country?"

The shift in domestic politics, he says, is reflected in the way that US foreign policy is being conducted. "They are trying to run the world as though it is a corporation and it doesn't work like that. You can't just give orders to people and expect them to follow them. The aim of the imperial economy is to reduce the rest of the world to peonage. The killer that gets off the plane in Argentina or Malaysia is the banker. The only line in the sand they're interested in is the bottom line."

It is these logical threads that tie the America of September 10 to the nation we see preparing for war today, he says. "What they have been lacking since the end of the cold war was an enemy, and then here comes Bin Laden with a jihad. It couldn't have been scripted any better as far as the Pentagon were concerned."

It is with a delight, verging on pride, that he tells the story of the failure of Henry Dearborn, his great-great-grandfather, who was given orders to move North and take Canada by September during the 1812 war.

It should have been a breeze. "Just march north and take the goddamn place," says Lapham with a dismissive waft of his cigarette.

By February 1813 Dearborn had only made it to the south bank of the St Laurence river when he finally gave the order to charge, and one of his generals raises four points with him. "First of all, it's cold," recounts Lapham. "Second, they have guns. Third, they are our friends and we depend on them for trade. And fourth, we are the New York state army, not the American army. We're not going."

Dearborn saw the logic of the situation and went back to Boston a failure. "In the long and distinguished list of bad American generals he was right at the top," boasts Lapham. "When people talk of the infallibility of the American military and the glorious descent on Baghdad I think of the not so glorious descent on Montreal."

· Theatre of War by Lewis Lapham is published tomorrow by The New Press, priced £12.95