Sheen presides over West Wing

On the tarmac of LA's Van Nuys Airport, Martin Sheen is imagining dead bodies in empty coffins.

A military operation has gone wrong and President Bartlet is greeting a succession of flag-draped caskets at Andrew's Airforce Base in Washington DC, for which Van Nuys, hosed down with cold water and billowing with fake fog, is doubling.

Flanked by a real military honour guard, Sheen as Josiah Bartlet, a president more liberal than Clinton and more uxorious than Reagan, looks, with each take, more and more affected. If his eyes fill any higher they'll burst their banks, but the directorial perfectionism of Aaron Sorkin's beguiling television series, The West Wing, demands more takes. And then more again.

Ramon Estevez, Sheen's middle son and personal assistant, has warned me to bring a coat. But the sun has barely set on this all-night shoot, and I'm already wishing I'd brought thermal underwear and a foil blanket. I am receiving strong hints that there could be a wait as long as a Florida recount before I get to interview Sheen, who, at 60, is blinking in his strongest beam of limelight since Apocalypse Now more than 20 years ago.

It is strongly suggested that I take this "opportunity" to chat with one of The West Wing's executive producers. And so it is that I retire to a nearby hangar with the one-time director of So I Married An Axe Murder.

Thomas Schlamme, a baseball-cap wearing slouch whose unlikely patriotic fervour is born of being the son of Jewish-German immigrants, surprises me by explaining that Sheen landed the part only because James Earl Jones and Sidney Poitier were unavailable. In fact, he was the last person to be cast.

Initially, the show was designed to centre on the White House staff with Potus (President of the US) making only cameo appearances. Then Sheen went and stole the last six minutes of the pilot: "And it was kind of nuts not to use him all the time." More than his Catholicism or even his politics, which are to the Left even of Bartlet's, Sheen, Schlamme says, brought almost precipitous degrees of personal charm to the part. "There is something so genuinely real and pure about him as a person. I think he is the real definition of reformation. It is a reformed life."

Born in Ohio to a Spanish factory worker and his Irish wife, Sheen was himself called Ramon Estevez until he arrived in New York in 1959 and, determined to become an actor, changed his name to something more bankable. After a decade on stage, he moved to Hollywood in 1970, still unsure about how to capitalise on his talent and embarrassed by self-promotion. Four years later, he was picked by Terrence Malik to star in Badlands as a naive killer with a face that was a dead ringer for James Dean's. He still believes he will never give a better performance.

Shortly afterwards, Francis Ford Coppola cast him as Captain Willard in his quasi-spiritual Vietnam epic, Apocalypse Now. It was a hellish, endless shoot. Sheen felt too old to play a soldier, was unfit and, surrounded by Philippine swamp, could not even swim. Improvising one key scene before the camera, he cracked up, lashed out at a Saigon hotel room mirror, cut open his hand and delivered a Heart of Darkness-style rant that eclipsed Marlon Brando's.

Six months later, still on location, he had a heart attack. He was 36 and almost died.

A period of drinking and gambling ensued, during which he briefly left his wife, Janet, the art student he had married in 1961 and the mother of his four children. As the Eighties progressed, however, he rediscovered his faith and signed up to Alcoholics Anonymous. He found a focus in political activity and, since his first "righteous arrest" in 1986, has been arrested in more than 70 demonstrations, the latest at the military base testing the Son of Star Wars technology. (Neatly, the second season of West Wing has Bartlet regularly humiliating his defence chiefs over their failure to make a missile shield work.)

Sheen's progress from faithless drunk to a devout activist who, along the way, has "been there" for his wayward Brat Pack sons, Emilio Estevez and Charlie Sheen - even to the extent of providing homes for the women who bore their illegitimate children - is what Schlamme means by Sheen's "reformation".

"Oh, you don't want to listen to Tommy," says Sheen, who, amazingly, is finally sitting opposite me, eating roast beef. With his thick head of hair and crinkly cornflower eyes, he looks undeniably statesmanlike, an impression compounded when he asks me for news of the Irish peace process. Sheen, whose uncle fought for the IRA, fears for it, as he fears for so much post-Clinton. "This man," he says, meaning George Bush, "is a moron, if you will pardon the expression."

I ask if Bush doesn't make The West Wing's cheery liberalism look absurd? "But we are a fantasy. And we were there first."

In the series' early days, Sheen says, he asked who Bartlet actually was. Schlamme told him he was whoever Sheen was and Sheen took the opportunity to fight for Bartlet to "come out" as a Catholic. But Schlamme's, I point out, were almost exactly the words Coppola used when Sheen asked the same question about Willard. So what is the difference between the Willard-Sheen of 1976 and the Bartlet-Sheen of today? "Oh, probably not a whole lot of difference. He's just got older and, hopefully, a little more mature, a little more human, a little more patient, a little less ambitious, a little more grateful."

He suggests that the core of your character changes less than your willingness to drill down to it. Willard's madness was "induced by booze, which will get you in touch with yourself very easily if you are at all sensitive". Coppola had actually wanted to stop filming, the scene had got so out of hand.

"But I said, 'No, Francis, let it go. This is mine.' I wanted to expose the demons. I wanted to see myself."

And had he? "I never looked at it until I saw the movie. Francis wanted me to see the rushes but I was so frightened. No one wants to look at their dark side."

A young woman wearing a headset says they need him to greet more body bags. "Tell them I'm choking on a potato," he says, but goes anyway.

My spirits rise after an hour's more shooting when the director shouts "Take lunch", but quickly fall again when I see that Sheen is not only determined to glad-hand every one of the Honour Guards but to sign their caps individually. The PR apologises: "Marty just wants to be liked by everyone."

When we spot him again he is in his caravan, pulling on trousers. I ask what the prognosis was after his heart attack in 1977. "I was young enough, fortunately. If you are going to have a heart attack have it when you are young because you have a better chance of survival," he says. "But I wasn't concerned with the medical part of it. I threw all the medicines in the toilet. My wife was my doctor and she led me through it. I knew it was as much an emotional, spiritual crisis as it was physical." And then he gets another call.

A horribly long time later, at about 1am, Sheen is excused. On the way to his trailer he runs into John Spencer, an old contemporary, who plays Bartlet's chief of staff. Looking as wild and whacked as Ben Gunn, he has been performing Glimmer, Glimmer and Shine downtown, a play Sheen shamelessly plugged in his acceptance speech when he recently won a Golden Globe for The West Wing. They embrace.

Sheen wants to know if the audience had stood. Spencer admits: "There was some cheering."

Back in the caravan, I ask, semi-satirically, if Sheen would have made a good president. He pauses, but not for very long. "Yeah, I would have made a very good president. But thank God I wasn't called to do that."

In fact, he says, he was approached by the Green Party to be Ralph Nader's running mate. "We polled six per cent with me as his vice-president and eight with me as his president. I was flattered. I fantasised about it. But it was ludicrous. It would be the end of your life. You'd belong to the public." (Nader finally took less than three per cent.)

I say I suspect he feels he belongs to his family. He says he fears his ego has prior ownership. But, I protest, Ramon and his sister Renee, who plays a secretary on the show, tell me he was a good father, if a serious one. "I was too damn serious," he says.

"If I were checking out [of life] and were given an opportunity to expunge something, make like it never happened, I would choose, without a question of doubt, to undo all of the violence towards my children, psychological, moral, spiritual and physical. That would be the one thing. I would never hit a child, having raised children. I would never dress them down. I would never humiliate them or make them feel less than human. I would not do that again."

In 1990 Charlie Sheen, his youngest son, went into rehab for cocaine addiction and two years ago suffered a stroke after overdosing on heroin. I ask if Martin had blamed himself. He says of course he did, but at least he had experiences he could share with his son.

"The great advantage to understanding addiction is to take for granted that the person using a substance is motivated either consciously or unconsciously by transcendence. It is a spiritual journey. I have met people who have sworn they have seen God on one substance or another and I don't have the slightest doubt they did. The problem is the journey does not belong to them."

The journey being? "It is the journey to self and the journey away from self and the journey to freedom. The more conscious you are of the journey to freedom, which is the journey to God, to the One, whatever you call it, the more the journey brings you back into yourself. That is my take on it. I may change my mind tomorrow. Or maybe in the next 10 minutes."

But it is well within 10 minutes that I realise I no longer understand what Martin Sheen is talking about. Like Coppola all those years ago, I even try to curtail the performance. But he wants to continue.

"The loss of the soul does not happen overnight," he says, in a preacher's timbre. "It does not happen with one visitation by the Devil. The Devil comes in many shapes and forms. It happens in increments and by the end you do not know yourself, except by the possession. You are not free."

After a while, I am alarmed to find he is beginning to ask me non-rhetorical questions. "What is the universe? You tell me what it is not. Tell me what it is."

Martin, I say, it's two in the morning and I don't know. "That is the point," he says triumphantly. "We don't know. We are not meant to know. You are the only universe you are going to discover and explore. The only one you will be responsible for. You own the universe. You have that knowingness. That is why you are an Artist."

This may be the nicest thing an interviewee has ever said to me, but I feel that even he suspects his eloquence - in its own way, an avoidance tactic - may now be doing him more harm than good. Yet, he invites me to write whatever I like about him, however critical. "It is your business. It belongs to you and I give it to you." And this is not all he gives, for he also hands me an elegant leather passport holder, which he signs in indelible felt tip: "Peace".

If there has been a theme to my extraordinary, three-act Night of Sheen, it has concerned the difficulties a modest, spiritually inclined man can have in a profession whose American branch, at any rate, treats wealth and fame as its truest values. Success has wounded him in the past and, I think, he fears it could harm him again.

He fights its spell with charms of his own; generosity, magnanimity, leather wallets. The result is that what I actually take back from California's Arctic Circle is a feeling of warmth. Real presidents have spoken less coherently, and have been elected for less.

The West Wing continues tomorrow at 10pm on Channel 4.