Several recent and upcoming Hollywood and television films, for example, explore the previously off-limits territory of gay and lesbian relationships. A few earlier ones (Basic Instinct and Silence of the Lambs come to mind) featured homosexual serial killers, but the current crop focuses on the interpersonal struggles of ordinary, non-psychotic gay and lesbian lives.

Going beyond homosexuality, which has already gained an unprecedented measure of tolerance within American society, three other new films delve into the world of transvestites and transsexuals, men and women who take pleasure in cross-dressing or even undergo surgery and hormonal treatment to physiologically change into their opposite.

In The Crying Game, a straight-and-narrow heterosexual falls for a sexy, working class chanteuse in London only to discover that she is a he. Orlando, based on Virginia Wolff's novel of the same name, follows the adventures of a man/woman through severalincarnations. Both movies have attracted far larger audiences than expected.

A MORE direct index of the public mood is tabloid talk TV - there were 20 such programmes at last count - for which sex, in all its possible permutations, has become a staple item. Donahue, Geraldo, Sally Jessy Raphael, Montel William - all of them turn,again and again, to the periphery of acceptable (and unacceptable) sexual behaviour to titillate and, incidentally, educate.

The constant barrage of fringe behaviour and alternate lifestyles has another effect: it breeds indifference, even tolerance. Line up six transvestites on the stage in front of a hostile audience, and watch what happens. At least a couple of them will come across as very sympathetic, and one may even be articulate enough to help others understand why he is the way he is.

A third arena in which the drama of changing sexual mores is being acted out is in the courtroom, where many of the same questions are addressed with the same degree of confusion as on television talk-shows: Should gays and lesbians be allowed to adopt? How does one draw the line between consensual and forced sex? Should gay couples receive the same benefits packages from employers and straight couples? The answers to these questions, and the search for sexual identity, have been made more, rather than less, complicated by recent scientific findings. Bio-medical research has almost certainly identified genetic and brain structures which suggest a predisposition to homosexuality.

But even if these preliminary findings are confirmed, what do they imply for a young man or woman trying to determine his or her sexual orientation? Which is more ''empowering'', to use a current buzz word, the knowledge that one is gay by preference, orby biological design? My wife, who has returned to school after a 10-year hiatus in the workforce, is among 19-and 20-year-old students in a university in New York City. Many of her classmates, she says, are exploring every kind of sexuality - hetero, bi, homo - to see where they fit into the spectrum. The saddest part, she says, is that they seem burdened rather than liberated by their choices.

Choosing a career was hard enough; now they have to choose their sex too.