Steve Buscemi was four years old and out shopping with his mother when he was caught short at the butchers. She took him home, just across the road, and told him to wait for her while she completed her order. But he got scared all by himself. He remembers it like yesterday. "I came out to the door, and stood yelling for her, but she didn't hear me, and I just panicked and ran across the street. I remember there were these high-street girls hanging out on the corner, and I remember one of them said, 'Watch out for the bus.' I must have looked the wrong way."

To say young Buscemi was accident-prone is an understatement. But he bristles at the idea that he was unlucky. No, he says, the opposite - he was lucky to get away with a fractured skull when he was hit by the bus. In fact, as it turned out, the accident might just be the most fortunate thing that ever happened to him, helping to pave the way for his acting career.

A few years later he was playing ball in the school yard when the ball rolled away from him into the road. He chased after it. Smack. This time he was lucky to get away with cuts and bruises when the car hit him. Sure, he was born on Friday the 13th, but he's not the superstitious type. Five years ago he tried to break up a bar brawl between his friend, the actor Vince Vaughn, and a stranger. For his pains, he was stabbed in his throat, face and arm. Perhaps that was his luckiest escape of all.

His characters don't usually get off that lightly, often coming to gruesomely sticky endings. As contract killer Carl in Fargo, he is described by a woman who has just slept with him as "funny looking, even more so than most men", before being hacked with an axe and fed into a woodchipper. In Ghost World, his younger-than-is-strictly-appropriate friend, played by Thora Birch, says he's such a "clueless dork, he's almost cool" - this time he ends up half-strangled and hospitalised. In The Big Lebowski, whenever he tries to talk, he is told "Donny, shut the fuck up." He's such a wimp that he dies of a heart attack when threatened with violence, such a failure that his ashes have to be kept in a Folgers coffee tin because the cheapest urn is too expensive.

Even when he gets to play seemingly cool gangsters, he's left disappointed. In Reservoir Dogs, the hoods receive colour-coded aliases and he ends up humiliated as Mr Pink ("Why am I Mr Pink?" "Because you're a faggot.") His characters mumble and bumble, querulous and whiny, but they are usually articulate philosophers of low-rent life.

In his new film, Interview, unusually he plays a high-achieving professional. Fear not, though - he's on the skids. As the hard-nosed correspondent Pierre Peders, reduced to doing puff pieces on soap stars, he takes self-loathing to a new low. The most remarkable thing about his characters is that against all odds we end up liking them. However seedy, pervy, dishonest, paranoid, infantile and psychotic, they always leak humour and humanity.

Buscemi grew up in east New York in an Italian-American family. His father, John, had hoped to be a television cameraman, but he ended up clearing garbage for the sanitation department. His mother, Dorothy, worked as a hostess in the Howard Johnson hotels. The Buscemis lived in a little apartment attached to a house owned by his grandmother and occupied by her five children and their families. His parents slept on a foldout bed in the living room while Steve and his three brothers shared the only bedroom. His grandmother had a little money when she arrived from Italy and invested in the house. But by the time it was occupied by five families it was cramped.

He went to a Catholic school, and when he heard his parents arguing, which was often, he used to pray for their salvation. "Whenever I heard them curse I would make a sign of the cross and thought that would be saving their soul." He was an anxious boy, worrying that if they argued when he wasn't around he wouldn't be on hand to save their souls. By the time he got to junior high school he had given up on God. "It's a terrible thing they do to kids, make them believe all this horrible stuff."

His father likes to say that he and his brother provided the inspiration for Buscemi's psychos. "He claims there is this Buscemi temper that's unique to Buscemis. I don't buy into it. His brother really had a temper. My dad had a temper. I have a temper. Most people I know have a temper. And I think it comes out mostly with your family. I don't think it's unique to the Buscemis, but it's something I've been able to tap into when I play certain roles. That's the fun of being an actor - you can act out all those violent fantasies." He remembers going on holiday to Sicily and hearing about two brothers in his family who had a fight, which resulted in one killing the other. He never discovered if it was true.

The night before our interview, he attends the premiere of Interview in London's West End and explains to the audience the genesis of the film. Although Buscemi directs and stars in the film alongside Sienna Miller, it is not really his film. Interview was originally made by the controversial Dutch director Theo van Gogh, who was murdered by a religious extremist after his short film, Submission: Part I, a condemnation of violence against women in Islam, depicted abused women with text from the Qur'an on their bodies. Before he was killed, Van Gogh had hoped to remake three of his films, including Interview, in America. After his death, his producers, Bruce Weiss and Gijs van de Westelaken, decided to realise his dream for him - which is when Buscemi came aboard. Interview is remade with Van Gogh's crew, using the same neo-realist techniques. Van Gogh's film is more intense and edgy (in it the Dutch actress Katja Schuurman plays herself); Buscemi's is lighter and perhaps better suited to an American market.

He introduces the Dutch crew and co-writer David Schechter, and it quickly becomes apparent that he is happier as part of an ensemble rather than hogging the limelight. In the film, the journalist does not prepare for the interview with the actress because he feels it is beneath him, and goes on to betray her trust. Buscemi stresses that the film is much more about the relationship that develops between the journalist and actress (two compulsive liars who pride themselves on seeking the truth in their work) rather than a treatise on media hypocrisy.

Not surprisingly, members of the audience at the premiere want to know his views on the celebrity interview. He retreats into classic mumble mode, says he doesn't really give them much thought, then concedes, yes, he doesn't care much for them, before finally admitting that "I turn into a zombie and then I start being hostile", and oh God, he's got one tomorrow morning at breakfast time.

The following morning I arrive for my breakfast interview with Buscemi. He's having his photograph taken, and I try to make filmic small talk. I tell him I saw Interview the previous night and it's obvious he's a big fan of the ground-breaking actor-director John Cassavetes. "Sure," he smiles. It's a typical Buscemi response. He's not rude, but he doesn't waste words. He seems at his happiest nattering about his 16-year-old son, Lucian, who plays guitar in a punk band. Years ago they used to wrestle each other off the sofa, but now Lucian is too big for him.

In the flesh, Buscemi looks much as he does in the movies - Bela Lugosi meets Stan Laurel. He wears the bewildered expression of a cartoon character who has just been flattened. His face is remarkable - the bags underneath his eyes have their own bags; the sockets their own shade of red, and his teeth are stacked like tins on a supermarket shelf. He is skinny and wiry, and, dressed all in black, resembles an animated shoelace. A strangely attractive shoelace. Steve Buscemi is not the stuff of leading men. Yet, occasionally, he does lead, and he is just about the best support or cameo player in the business.

As a kid, he used to watch a huge amount of television, especially movies, and he set his heart on acting. He loved his extended family set-up in New York, but dreamed of Hollywood. After all, his father's close friend, Peter Miller, had managed the same successful transition, and had even starred in Robert Altman's first film, The Delinquents. Occasionally, Uncle Peter would return to New York and Buscemi would question him about the business. "So in the back of my mind it was possible. Here was someone from my background and neighbourhood who did become an actor. But he didn't have connections to help me." In fact, Uncle Peter ended up as an investment banker.

At school he hung with the hard boys, and made them laugh with his clowning. He was strong, but not tough. Buscemi wrestled for the school and says he was far more successful as a team wrestler - knowing that the team relied on him for a win spurred him on. Was he a hit with the ladies? "No. I never had a girlfriend." He stops to correct himself. "I had a girlfriend for two weeks in ninth grade when I was 13, and then in high school I had another girlfriend for another two weeks. And that was it." The first time he had a proper girlfriend, he says, was in 1978 when he was 21 years old.

His father was anxious that the Buscemi boys should have a stable future, so he insisted on them taking their civil service exams when they were 18. Steve passed his for the fire department. "He wanted me to have a good, secure job. He told me that if I became a firefighter I could retire after 20 years on half pay, and then I could be an actor."

But Buscemi was determined to go to Hollywood. John Buscemi didn't want his son to be an actor, but he wanted him to leave home even less. So he compromised. He told Steve that he could go to acting school in New York - and that's where the bus accident came in handy. At 18, he was due to receive $6,000 compensation from New York state for being run over, and his father suggested he use it to put himself through drama school. "So it paid for the Lee Strasberg Institute and I also bought a used car, and it kept me afloat for a while." He also supported himself as a petrol attendant, furniture mover and ice-cream man. He liked selling ice cream, and the kids liked him.

Buscemi initially found the Lee Strasberg Institute "intimidating" (a word he often uses) - both mixing with a more privileged class of people, as well as the school's dogmatic insistence on "the method". He relaxed when taught by Lee's son, John, who told him that any technique was fine so long as it achieved the required results. "They had this thing where if you were in a desert and imagining sun beating down on you, you couldn't use the stage light to imagine the sun. But John said if the stage light works that's fine. The audience don't know and don't care."

In the evenings, he tried his hand at stand-up. "It was mostly self-deprecating and observational humour. Not very original. Which is ultimately why I stopped doing it. I couldn't find a voice."

All the time, his father was hoping he would make good and take his place in the fire department - which he eventually did in 1980. Buscemi spent four years working as a firefighter. "What I really loved about it was the camaraderie; how close you got to the people you worked with." Because they were putting themselves at risk? "Yeah, absolutely. And also a lot of time spent together in a fire house. Most of the time you were waiting. There were a lot of days when nothing happened." Were they the good days? "Erm, most firefighters would prefer to go to a fire even though none of them wish ill on anybody. But you want the experience, which is why some firefighters will purposely try to get assigned to the busiest areas in New York where they'll see more fires. I was stationed in Little Italy, so we weren't slow but we weren't busy, we were moderate, and that was enough for me." Occasionally, he says he has experienced a similar camaraderie as an actor, particularly on a first night at the theatre.

As he worked for the fire department by day, he acted with experimental theatre groups such as the Wooster Group by night. He also teamed up with Mark Boone Jr to form the surreal performance duo, Steve And Mark; after a piece called Yap Thaw, in which they mutated from dogs into men, the New York Times described them as "An intellectual East Village variant of the classic male comedy teams... A satisfyingly Beckettian comic turn." It was around this time that he met his future wife, Jo Andres, three years older and already established as an avant-garde artist and choreographer.

In 1984 he quit the fire service to focus on his acting. Although he was 29 years old when he made his movie debut, remarkably he now has more than 100 movies to his name. Equally remarkably, he rarely makes a bad choice. Buscemi has worked with virtually all the great contemporary American independent directors (Martin Scorsese, the Coens, Jim Jarmusch, Quentin Tarantino, for starters), and has given us some of the most memorable characters of the past 20 years. When he goes blockbuster, as with Armageddon or Con Air, he also tends to hit the bull's-eye. These days he makes the big films to subsidise smaller projects that he directs himself.

Trees Lounge, the first movie he directed, was a great cult success. It's a lovely, low-key film about a drifter, Tommy, selling ice creams and finding himself involved with a girl too young for him. Again, he says he initially found directing "intimidating" but he has learned to enjoy it. His directing career has met with mixed success - Animal Factory, set in a prison and written by Reservoir Dogs' star and old-time lag Eddie Bunker, had only a very limited release in Britain. Lonesome Jim, a comedy about a 30-year-old low-achiever moving back with his parents, didn't get any release in Britain. Perhaps his best-known work as director has been on the television series, The Sopranos, in which he also acted.

However high-profile he has become, he's never quite got the fire department out of his head. And the day after 9/11 something strange happened. Buscemi found himself putting on his old gear and heading for the collapsed World Trade Center. He didn't quite know what he was going to do, it just felt right. "The first day I went on my own and walked around and got closer and closer to the site and found the guys I used to work with. You couldn't get on the pile where the buildings had collapsed without special permission. Any company that had lost guys had access to the pile. They were actually taking a break outside the pile, when I found them. You couldn't tell what anything was. It was such a bizarre, surreal experience. I told them that I would like to work with them, and they asked me if I had gloves. I said 'yeah'. But I didn't have gloves that morning - I had to go and buy them."

Buscemi spent five days with his old colleagues, cleaning the rubble, working the bucket lines. It had a massive impact on him, helping him through the tragedy of 9/11 but also forcing him to question his motives and reassess. "It was strange because I felt totally safe there, and I felt good being there. All I was doing was digging and putting rubble in buckets and passing it on, and then it got really weird whenever there was a body bag coming along, or helping to take a body bag to the makeshift morgue. I was grateful for the opportunity to be reconnected with these guys I used to work with."

He enjoyed that old spirit of solidarity, though he felt he shouldn't have been enjoying anything. "On the fifth day it became obvious that I was standing around more than I was helping, so I decided I didn't want to be in the way - the last thing I wanted to be was just a person down there who wasn't doing much. So I stopped going. It was only then that I experienced the deep depression of what happened, the horror of it, the fear and the anxiety. While I was there, and with those guys, I felt good, yeah."

So it was a way of coping? "Absolutely. I went there to help and they ended up helping me. Being with my old company, being with everybody down there, was very... life-affirming." He squirms at the irony of the word. Did he consider rejoining the fire department? "It was too late for that," he says tersely - he will be 50 in December. Did he consider going back to a "real" job? "Yes. But I don't know what I would do. I suppose that's part of the reason I want to direct more. You use more of your brain, and it's more responsibility."

Later that day, when being interviewed on stage at the National Film Theatre, Buscemi is asked how he has avoided being typecast. He hasn't, he says, with typical bluntness. He tells the audience of his very first film role in a little known movie called Parting Glances, playing a man with Aids, and says it's still one of the movies he is most proud of. "The character was smart, funny, acerbic, and after that film I expected to play more parts like that. It was a big surprise to me to be cast as psychos and criminals." Now, he says, only half joking, if he is to be cast against type, he has to make the film himself.

Perhaps it's not surprising you so often get cast as psychos and losers, I say, when you play them so brilliantly. For the first time, I experience a hint of the hostility. As he talks, he morphs into the man we have often seen on screen - whiney, argumentative and surprisingly tough. "I don't see any of these people as losers. I refuse to call them losers. I don't see why people have to be defined as winners or as losers. To me, they are people who have problems and struggle. They are trying to live their life and a lot of these guys have a lot of heart, which I really appreciate." He cracks his fingers.

I'm still trying to tell him why I love his acting. I find myself burbling about class consciousness and Buscemi being rooted in the blue-collar world of his own past. "Are you so good at playing them because of your own experiences?" I ask, embarrassingly.

"Good at them?" he asks with disdain. "You still calling them losers?"

"Yeah, I suppose so," I say.

"But why? I don't understand why you view them as losers." Well, they aren't winners, are they? "Yes, but they are also people who are not interested in being in the race. They are not competing, they are not winning or losing. It's living, surviving."

This is what makes Steve Buscemi such a great actor. We might regard his characters as weirdos, sickos and losers, but he doesn't. He always empathises with them. Of course he does. After all, he's just a normal guy trying to get by, playing normal guys trying to get by.

· Interview goes on release on November 2.