This season's Updike is a sequel to The Witches of Eastwick, and he's already at work on the novel after next, a tale of ancient Rome. In a rare interview, he talks of women and witchcraft with Peter Conrad, before dismissing Sarah Palin as a 'bird-brain', doing a wicked impression of John McCain and endorsing Obama for President

'Lately,' said John Updike, 'I've been feeling not so much a wish to die as a wish that being alive didn't generate so many demands.' Sitting across from Updike in a Boston hotel suite with my notebook open, I was the demand, and I have to say that he looked equal to it: now 76, with a wintry shock of white hair, his eyes gleamed in his angular, bevelled face, and his mouth curved in wry amusement. 'You write a book,' he went on, 'and that generates demands, like this interview - though of course I'm sure it will be perfectly delightful!'

Incorrigibly prolific as he is, Updike has only himself to blame for the demands that admiring readers make on him. 'Back when I started, 50 years ago, our best writers spent long periods brooding in silence. Then they'd publish a big book and go quiet again for another five years. I decided to run a different kind of shop, on the English model you might say, with a much more regular output. I still want to give my public, such as it is, a book a year.' He is now at work on the book after next, a novel about ancient Rome, which will join the queue for publication after a volume of short stories that is due in 2009. Meanwhile this season's Updike is The Widows of Eastwick, in which the sorceresses from The Witches of Eastwick, published in 1984, return to the rampage, with conjuring sprees in Egypt and China before they revisit the sedate New England coastal town where they re-erect their cone of gynocratic power.

'I suppose sequels are inevitable for a writer of a certain age,' Updike sighed. 'When I re-read the earlier book, I was struck by how rich and dynamic it was, if I may say so - by the energy there was in the women and their magic. They're paler now, somewhat filmy. They are crones, after all. But they do less harm this time: they're violent in the first book, they kill a rival. That was my warning to the feminists, since the peaceniks in the Sixties claimed that women in power would behave better than men, be gentler and kinder. If that were true, how do you account for Golda Meier and Margaret Thatcher? Now my widows are trying to atone for some of the damage they did.'

Alexandra, the leader of Updike's coven, rejoices at the chance to release her 'inner witch'. Did Updike, I wondered, have his own inner wizard, concealed somewhere beneath his patrician uniform of navy blue blazer and rigorously ironed pants? He chuckled and looked enigmatic. I was referring to his uncanny imaginative empathy, which extends beyond other human beings - the wickedly skittish Harry Angstrom (nicknamed Rabbit) in the sequence of novels that began with Rabbit, Run, the tribe of copulating suburbanites in Couples, or the hundreds of quirky individuals who populate his short stories - to non-human creatures. His recent Shakespearean novel, Gertrude and Claudius, imagines how a horse sees the world, with two uncoordinated eyes looking in opposite directions. Couples transcribes a hamster's fumbling stream of consciousness, and in The Widows of Eastwick Alex fantasises about being a crab, 'moving sideways on tiptoe with eyes on stems', or a barnacle, 'standing on your head in a little folding bucket kicking food toward your mouth'.

'Did I actually write a soliloquy for a hamster?' asked Updike. 'Ah well, it's all the same for me. I'm happy to be Rabbit, or to be a crab. Barnacles amaze me - how unlike us they are, the monstrous ways in which the poor things have to contrive to have sex. When you sit at your desk, if you're lucky there's a moment when you feel empowered to be someone or something else, to leap into another skin. It's what Keats called negative capability. There has to be some gap between you and the other life, which the creative spark can jump across.'

Updike once told an interviewer that the breezy way in which he surveyed his characters from above as he arranged their futures at the end of Couples gave him the sensation that he was flying. Magicians, whether male or female, surely feel that way too. Was he, I asked, a senior Harry Potter? 'Hm,' he said, not sure whether I was teasing him. 'Rowling - is that her name? - certainly brought magic back into our minds, though it's always been there. What interests me is why men think of women as witches. It's because they're so fascinating and exasperating, so other. There's such a psychological gap between the sexes. The erotic impulse jumps across that distance, like the creative spark. Maybe that's what I meant when I said I was flying.'

In the Eastwick novels, magic is Updike's way of liberating the anarchy of nature, repressed and disciplined by scientific laws. The witches worship a 'creatrix', otherwise known as Mother Nature. Darryl, the lover they share in the first novel, pays tribute to this pagan goddess as he splashes with them in his hot tub: he marvels at the fecundity of the female body, able to incubate and expel new lives. This homage to creativity is aesthetic as well as religious. I suspect that Updike, from whom books continue to pour, shares the polymorphous slipperiness and the fertile abundance of his witches. But I found the question difficult to phrase. How do you ask an upright grandfather if he feels androgynous, or get a church-going Wasp to admit that he possesses devilish talents?

Updike smiled as my tact got my tongue in a twist. 'Well, I'm reminded of something the prophet Tiresias said after a magic spell turned him into a woman for seven years. He was asked whether the man or the woman had greater pleasure when they made love, because he'd experienced it both ways. He replied that sex was infinitely better for the woman! My three witches are artists - a sculptor, a musician and a writer - because I think that for women living is itself a work of art. I love the way they put themselves together in the morning, the way they prepare their faces - mostly for other women, because men are too crass to notice. Men don't have this aesthetic sense about life; they see it as a job to be done, something to be got through. And I enjoy the fact that writing novels lets me get interested in female things like clothes and furniture and food, all the domestic stuff men usually overlook. So maybe you're right about that.'

Down on earth, without a magician's wand to alter reality, I found Updike preoccupied with the obligations of citizenship, anxious about the outcome of the presidential election. His characters keep whoever occupies the White House in their peripheral vision, and often take the cue for their own behaviour from the frailties or vices of the chief executive.

In Couples, the assassination of Kennedy is noises off, dimly apprehended by the heroine, Foxy, as she lolls in a dentist's chair; the disaster does not cause the cancellation of a party the wife-swappers have organised for that evening. 'Yes, I loaned Foxy my own memories of that day,' Updike recalled. 'I was at the dentist near here in Brookline, and I remember when the easy-listening station on the radio they played to keep the patients calm interrupted some pop song for the news from Dallas. At first it was just the report of a shot; by the time I stepped forth on to the street, flashing my new crowns, Kennedy was dead and Johnson was being sworn in to replace him. I love that decision to go ahead with the party. Politics was really far from central to people's lives in the early Sixties; it was all about the discovery of the private life. And Kennedy was a hedonist and an adulterer too, of course. I was a naïve boy in those days, a bit shocked to realise that my patriotic and religious values were fading.

'Oddly, Lyndon Johnson reminded me of my father, which left me with very mixed feelings about the Vietnam protesters who brought him down. My father was a good teacher but not a disciplinarian; he didn't have the terroristic instinct you need to keep a class quiet. And I made life difficult for him myself, because I was naughty to win the approval of my peers. So I felt guilty about the protests, which wasn't the general mood at the time! It's an unpopular opinion, but I think the President should be respected. It's a terrible job, you can only lose at it. It's an insanity to want it, in fact.'

That sympathy even extends to the current incumbent. 'I think Bush got pushed into it, and he'll probably be happy to get out. He gave me an award in 2003, the National Humanities Medal, and I was touched by the way he handled things. He'd been in meetings about Iraq all day, he was weighed down by that, but he wanted to make each of us who were getting medals feel the moment personally, so he had to be presidential - and, for as long as the ceremony lasted, he was.' Updike was luckier than he might have been if he had turned up at Buckingham Palace to be gonged: the Queen would have wearily asked if he was still scribbling, then waited for him to move along.

We spoke on the day of the second presidential debate, in which McCain, strutting and frothing, dismissively referred to Obama as 'that one', as if unable to bring himself to voice his rival's suspiciously exotic name. 'I'm for Obama, 100 per cent,' said Updike. He has a personal reason for his enthusiasm: his memoir Self-Consciousness is dedicated to his two half-African grandsons and contains a letter to the boys, assuring them that all Americans are 'of mixed blood'. 'Things have moved on since I wrote that. I now have three grandchildren who are Obama's colour: my daughter married a Ghanaian, and my son has a Kenyan wife. The colour brown has come around, as the song says!

'I really think Obama would regenerate this worn-out country. I'm such a believer that I probably won't be able to watch the debate tonight. I get so upset when I think about the alternative. McCain is blameable for choosing Palin as his running mate. She's a bird-brain, she annoys me terribly. McCain himself is worse. You know the way he grits his teeth? Mine grit too as I watch him.' Novelists, like actors, create character by an act of physical identification, which even extends to someone they despise. Opposite me on a couch, Updike's teeth froze, his arms shortened and stiffened, and his sparkling eyes turned wild. The magus momentarily became the grizzled, barking, Republican nominee.

I told Updike that both Obama and McCain had nominated him as one of their favourite writers. 'They did? I'd have thought Barack would be reading Hegel, not fiction! And I can't imagine McCain reading anything. He's so irascible, readers have to be patient.' Just in case the candidates were bluffing, I asked Updike to assign one of his books to them as required reading. He made a lattice of his intertwined fingers and sunk his face into it: this is his portable, manual cave, into which he retires to do his thinking. He spent a while perusing his back list, which after all comprises 23 novels, a dozen collections of short stories, an equal number of volumes of critical prose, half a dozen collections of poetry, five books for children, a play and an autobiography. Then he re-emerged into the light, beaming.

'Here we go. For Obama I'd recommend a novel of mine called The Coup. It's about an imaginary African country where the dictator pretends to hate the US, though he actually went to college here. The politics were based on Gaddafi - what's he called, not Mohamed, Muammar, right? The joke is how unlike Obama my character is! Now for McCain. I think he should read another novel, Memories of the Ford Administration. It's about an academic who hardly remembers Gerald Ford's term in office because he was too busy committing adultery and researching James Buchanan's presidency. Buchanan was old, tired, ineffective, and failed to prevent the Civil War; Abe Lincoln succeeded him. Maybe if McCain read the book he'd have the humility to realise he should gracefully yield to a younger, brighter man. Or maybe not.'

Enjoying the game, Updike was reluctant to stop playing. 'I could assign books to the vice-presidential candidates too,' he chuckled. 'Let's see. Palin is religious and so I am. She should read A Month of Sundays, which is about an errant minister rehabilitating himself in the Arizona desert. Who knows, maybe McCain's ranch is nearby? The book is as goofy as Palin, all brightness and gloss. And I want to give something to Joe Biden, Obama's running mate. He reminds me of the good-natured, diligent guys I grew up with in smalltown Pennsylvania. For him I'd say it ought to be any one of the Rabbit books - maybe the second, Rabbit Redux, in which my deplorable character at least appears as a working man. How's that?' Updike's satisfaction was deserved: in his store there is a book for every occasion, which justifies my belief that he has imagined everyone and everything, prescriptively narrating the lives that the rest of us lead.

As I left, news spread of Wall Street's latest giddy lunge into a gulf. 'This credit crunch,' said Updike, 'reminds me of something that Saul Bellow said - that we're obsessed with the afterlife, though we want it now rather than waiting until we get to heaven.' Despite Updike's delight in what he calls the world's 'muchness' - its thronging people, its blossoming vegetation, its rabbits, toads and barnacles - he is dismayed by excess and surfeit, by an American grossness embodied in the waddling obesity of his fellow citizens. Affluence has supplied the wrong kind of earthly paradise; the 'indulgent economy', as Updike called it in Couples, has subsidised our greed. His reference to Bellow reminded me, however, of Updike's own story The Afterlife, in which an elderly American on holiday in England survives a nocturnal fall downstairs which may be his symbolic tumble into death. Next day, reborn, he goes on a trip to the coast, and sees a world made new and radiant by metaphor: electric pylons resemble a host of angels marching across the land. The earth becomes heavenly when Updike writes about it. He has done more to enrich us than all of Wall Street's bankers and brokers, and his books, unlike the papery profits of the Stock Exchange, will not lose their value.

• The Widows of Eastwick is published by Hamish Hamilton this Thursday, £18.99. To order a copy for £17.99 with free UK p&p, go to observer.co.uk/bookshop or call 0870 836 0885

Updike in chapters

Early life

1932 Born 18 March in Shillington Pennsylvania. His father was a teacher and his mother a writer.

1950 Studied English at Harvard where he edited student satirical magazine The Harvard Lampoon

1954 Took a year-long fellowship at the Ruskin School of Drawing and Fine Art in Oxford.

Career

1955 Joined The New Yorker, contributing poetry, stories and editorials.

1959 Published his first novel, The Poorhouse Fair

1960 Published Rabbit, Run

1963 Received the first of many awards, the National Book Award for his novel The Centaur (right).

1982 Won the Pulitzer prize for his 1981 novel Rabbit Is Rich

1991 Won a second Pulitzer for Rabbit at Rest.

Family life

Married twice. Has four children with his first wife, Mary, whom he divorced in 1976. Lives with his second wife, Martha, whom he married in 1977.