For a minute or two, John Irving had the hangdog air of a boy dragged in to meet an elderly aunt. He looked at his feet, and then, lifting his head a fraction, stared at the brass candlestick on his dining room table as if he had never seen its like before. In the time that it took him to slip into another guise, he appeared to be wrestling with the impulse to cut and run.

Perhaps I imagined it. This was, after all, the John Irving whose image loomed everywhere after the publication of The World According to Garp, the literary phenomenon of the decade. When his next novel, The Hotel New Hampshire, was about to be published, Irving was on the cover of Time. Dark-eyed, tousle-haired and handsome, he posed, hand on hip, in a stance that hinted at Hemingway's aggressive physical presence.

In person, eight years after Time had hailed him as " the most successful 'serious' young writer in America", he seemed to have receded. It was because of his age. Irving, 47, could pass for a guy in his 30s, going prematurely grey. But he was faded in contrast to the photographs, as if, in the camera's eye, the man looked more like himself and he did in the flesh. By now he was wandering through his house with the photographer in tow. Irving lives in Sagaponack, Long Island, New York, but the materials for his house were hauled in from Vermont by a builder who re-rendered a century-old farmhouse a stone's throw from the Hamptons, the summer playground for Manhattan's elite.

Irving was anxious to have it understood that he had arrived on the scene when the house was more than half built. "Journalists always get it wrong," he told me, and since it was almost the first thing he had said, I wrote it down obligingly, wondering why he thought the people in Australia would care one way or the other about the provenance of the old pine beans and wood-panelling in a house on the other side of the world.

Several of the rooms downstairs at the curiously impersonal elegance of the illustrations in a home-decorating magazine, as if the pine dresser with its French country plates, the pine chests and painted cane chairs had arrived tout ensemble, but there was a distinguishing feature. Covering the walls here and there were dozens and dozens of snapshots of Irving and his family, doing ordinary things and looking happy.

Irving had gone outside with the photographer, Maryanne Russell, and considering that he had spent the first seven or eight minutes with us in an attitude of constrained civility that as good as said " let's get this over with as quickly as possible", he amost appeared to be enjoying himself. He posed on the deck around the swimming pool, changed expressions as reflexively as a model. He posed by the door of the big red barn next to the house. He posed on the stone steps leading to the garden beyond the pool, and still managed to look pensive posing in front of a blue spruce in a small grove of trees.

"There are writers who deliberately choose obscurity," Peter Matson, Irving's friend and literary agent, told a reporter a couple of years ago. "John is not one of them." Nonetheless, Irving seemed detached, and when we were sprawled out on the deck, with the tape recorder going, he spoke about the characters in his fiction as if they were more real to him and any person made of flesh and blood.

His novel A Prayer for Owen Meany was published in Australia last month. Irving's fiction teems with misfits and oddballs who are susceptible to disaster, and this novel is no exception.

Meany, a pint-sized caricature of Christ who speaks in "a strangled emphatic falsetto", dies in an airport broom closet surrounded by orphans and nuns. Meany's disciple, Johnny Wheelwright, the narrator of the novel, isn't merely short on presence; he's an empty shell. When his hero dies, Wheelwright flees to Canada, but his life is more or less over. "He's a damaged man. He has, in his own words, been neutered by his experience," said Irving, "and he is even teased by his own students. He's like an old snapping turtle. If you poke him with a stick, he'll do what he always does…"

Irving, who likes to say that he "tell stories about victims", created Meany and his sidekick as victims of the Vietnam War, and it let's him sound off about the 1960s, an era that he blames for almost everything that is wrong with his country today, from its social decay to its fifth-rate politicians to its fundamentalist airheads.

Neither the theological props nor the shrill polemics seems to have put people off. In the United States, the novel is a bestseller, his fourth since Garp. That book sold 3 million copies in paperback and gave him a cult following. Irving had published three novels before Garp, but the sales were abysmal. He and his wife and young son lived from hand to mouth. In one incarnation, which was to feature in a novel, he sold peanuts at college football games. He taught for a semester or two at obscure universities, he coached college wrestlers, and he continued to write for three or four hours a day.

When Garp made him rich, Irving was freed to work at the typewriter all day long and to turn out one big fat book after another. He admires "old-fashioned 19th century novels" – sentimental novels full of character and incident – and his readers appear to like what he makes of them. On the wall at the office, there's a huge blow-up of the best-seller list from the New York Times Book Review in 1985, with his novel The Cider House Rules in first place.

Closer in its dense texture to the "big Victorian novels" which inspire him, The Cider House Rules is about abortion. Irving, who advocates free choice, is working on a screenplay of the book. "The director, Philip Borsos, is a Canadian," he said, "and given the political cowardice about the abortion issue in this country, it will be a lot easier to raise money for the film in Canada. If it's made properly, it will be a very ugly movie."

The idea gave him evident satisfaction. He wants to make mischief, one reason he breathes life into characters who are grotesques. Irving himself loves them. He was to tell me, for instance, that he felt "exceptionally close" to Owen Meany. I was intrigued. It's not every day that an author admits to a particular affinity with a mock-up of Christ, however freakishly small. In fact, it is impossible to imagine a character more aggravating than Owen Meany, a manipulative know-it-all who bosses everyone about, from morning to night. He doesn't merely speak in a voice that gives people the willies, he speaks in CAPITAL LETTERS every time he opens his mouth, and as if that weren't provoking enough, he always gets the last word.

"Why do you feel so close to Owen Meany" I asked.

"No, let me finish this first," said Irving, who had launched into a lecture on literature. It had started because I had said that Meany's disciple, the peevish Wheelwright, very often seem to function as a mouthpiece for the author's indignation about the state of the union. Irving not only disagreed, he hinted that I had confused first-person narrative with the voice of the author.

"I feel there's a great naivety in people who read novels today," he said. "Maybe they have been out of school for too long." If he happened to write a play, he went on, in which there was a character addressing the audience directly, everyone would know that it wasn't the author speaking. I turned out for a bit.

The tape-recorder was going, after all, and I was more interested in figuring out why Irving, right there, on the deck, was doing something I had seldom seen in an interview. He was turned away from me, talking, quite animatedly, into the air. It had been evident from the first that he was intent on keeping himself under wraps, as if to reveal as little as possible about his personal life. I was familiar with the official facts, published countless times in countless interviews.

He had grown up in Exeter, New Hampshire, a town which features ( under another name) as the setting for Owen Meany. His mother had divorced his father and remarried by the time he was six. Only the press insisted on referring to the lrving Snr – the man he regarded as his real father – as his stepfather, he told me, sounding irritable, when I had asked about it. I refrained from adding that I had raised the question because his fiction included so many deserted women, single mothers and orphans. Remarks like that annoy Irving, who will say personal details "are relevant only to writers who don't have the imagination to do much more than give you an autobiography and call it a novel".

A few other facts about him appear to be set in cement. His father had taught at Philips Exeter Academy, a famous fancy prep school, which meant that Irving had been accepted there as a day boy. In speaking of his time at school, he said, "I found it a very safe and protective environment." I didn't know what to make of that.

The one thing Irving usually fails to deny is that he sees danger wherever he looks. His characters die violent deaths or are maimed in bizarre accidents. In The Hotel New Hampshire, he piled on the agonies with such relish that one reviewer noted the "motiveless malignity" of many of its scenes.

Irving has since managed to subdue himself a bit, and in the finest comic scene in Owen Meany, the only person who is actually injured puts his back out. In fact, the book is crammed with comic incident, but the author seemed determined to conceal that, too.

That lecture on lit. over, he had doubled back to mention Wheelwright again. Though he happened to agree with quite a lot of the opinions Wheelwright voiced, he said, that was beside the point. "I know and million Johnny Wheelwrights, and most of them don't live in Toronto. They live right here and they have politically dropped out. They stopped paying attention to anything in American politics – except to sort out of be angry with it – at the time of the Vietnam War . . . and when someone like Ronald Reagan is president."

Irving chuckled, unexpectedly, "It's very easy for them to say, 'oh, there you go again'. Where has the spirit of protest from that generation gone? It's gone into making money for themselves."

He was so fervent that it took me a moment or two to notice that these were platitudes.

For some reason, it reminded me again if the irritating CAPITAL LETTERS in the novel. Irving, loves explaining the devices in his work, had said: "Obviously, it's meant to coincide with the equally irritating red-letter editions of the Bible, but everything Christ says is in red ink." It hadn't been all that obvious to me. What was obvious was that the capitals appeared to be pregnant with meaning.

That was what people liked so much about his work: along with its antic characters and it's dizzying twists and turns of plot, it had the feel of something serious and important. Irving couldn't have calculated it – he doesn't write to a formula. But by chance his fiction gives people what many seem to want from big books: Big Themes in small bits.