Gore Vidal - the very name is like an anagram. At a London dinner party the other night, we came up with dozens, including valid ogre, grave idol, a viler god, and I love drag. Just as the vowels and consonants in his odd name (14 points' worth in Scrabble) lend themselves to endless rearrangement, Vidal has constantly rearranged the terms of his own life: prolific novelist, essayist, critic, political candidate, screenwriter, playwright, sexual radical, international socialite. As one admiring academic has noted, Vidal is "the Forrest Gump of 20th-century culture," a man who has managed to intersect the life "of virtually every literary, political and social figure since his birth in 1925".

Born Eugene Luther Gore Vidal, Jr; grandson of Tennessee's Senator Thomas Pryor Gore; son of a West Point aviator who advised FDR; stepbrother of Jacqueline Kennedy Onassis, Vidal had his first sexual experience at the age of 11, published one of the first American novels about homosexuality (The City and the Pillar, 1948), ran unsuccessfully for Congress in 1960 and has shared his everyday life, but not his sex life, with Howard Austin in a splendid villa in Ravello for decades.

In the past five years, Vidal has published his own somewhat chilly memoir, Palimpsest, been the subject of a weighty biography by Fred Kaplan and had a volume of his "essential writings" appear. In this collection of essays, reviews and interviews, he speaks more or less specifically about sex, on which he has long held strong, idiosyncratic and amusing ideas. In brief, Vidal believes that the main problem of our planet is overpopulation - we are "breeding ourselves into extinction" - and the real "agents of our destruction" are those who would "outlaw abortion, contraception and same-sex, while extolling the family". He argues that homosexuality is nature's form of birth control, and that gay sex is reasonable and useful.

But he does not see himself as a homosexual writer. On the contrary, he insists, "there is no such thing as a homosexual person. There are homosexual acts." The artist must resist categorisation and the ghetto: "Every state tries to categorise its citizens in order to assert control of them." Like all human beings, he declares, he is bisexual. Vidal has stuck to these terms of personal neutrality despite the best efforts of gay activists such as Larry Kramer (whose passionate interview/ conversation with Vidal in 1992 is the best piece in the book) to persuade him to declare himself a proud gay man. "But Gore, you are gay. You've lived with a man for 40 years or something, and everyone who knows you personally knows you're gay. And I think you think of yourself as gay." Kramer points out that if Vidal's role model, Tennessee Williams, were still alive, he would be writing about gay relationships and Aids. I wonder.

But one of the disappointments of this collection is that most of the essays are so dated (most from the 1960s and 1970s), that they not only predate Aids, but also miss out entirely on the recent trend for gay adoption and for same-sex marriage. What happens to Vidal's argument about breeders when lesbian couples are having babies and gay men are sperm donors? How much does his view of sexuality actually depend on specific social customs, rather than fundamental truths? While Vidal has not re-examined his basic beliefs (that a "heterosexual dictatorship . . . goes on its merry way, adding unwanted children to a dusty planet while persecuting the virtuous nonbreeders") for the past 35 years, the evidence from these essays is that his view of sexuality is much more determined by his idols and his enemies, by his prejudices and social preferences, than by biology or politics.

Thus the essays about sexuality are full of contradictions. Although Vidal denies that homosexuals as such exist and that he thinks in binary terms, he is vitriolic about anyone he suspects of criticising homosexuality. Many of those he singles out for attack are Jews - "the odious homophobe, Philip Roth" and "the shrill fag-baiting of Joseph Epstein, Norman Podhoretz, Alfred Kazin" - leading to charges that he is anti-Semitic. More revealingly, Vidal is obsessed with closeted homosexuals in history, with a retrospective "gaydar" that reminds me of my own father's proud conviction that most famous film stars and politicians were really Jewish. He is "fairly convinced" that Lincoln had a gay relationship; George Washington had a thing going with Alexander Hamilton; Melville was in love with Hawthorne.

Vidal is at his critical best, his wittiest and most sympathetic in his review of the complex and conflicted Somerset Maugham, who also avoided dealing with homosexuality and lived the high life in Capri, an "artful dodger", writing popular novels and plays that Vidal persuasively defends as literature. Maugham inhabited an elite European society that did not ask too many direct questions. He played it too safe, Vidal thinks, and became cruel in his old age, even trying to disinherit his own daughter. But this "half and half" writer retains his magic for Vidal, who started to read him in adolescence and still finds passages worthy of Chekhov or Austen.

Yet I find it dispiriting that Vidal is so nostalgic for Maugham's antiquated sexual persona, and that he continues to avoid and evade the sexual issues raised by Kramer's post-Stonewall, post-Aids generation. Once a daring iconoclast, Vidal is in danger of ending as a stately queen, noting in one aside that these days, sex has become so routine a pastime that young people no longer bother to learn bridge. It would be one of the great ironies of modern letters if this avid ogler were to end up as a large void.

Elaine Showalter's most recent book is Inventing Herself (Picador, £16.99)