Last Night in Paradise: Sex and Morals at the Century's End.

KATIE Roiphe's latest book, Last Night in Paradise, is suffused with a longing for innocence, which she locates in the Sixties' naive certainty that "bikinis from France, and the Pill, and nudity in movies, and honest and open marriages, and no-fault divorces would crystallize into the perfect society." However, being a post-modern girl, Miss Roiphe has an ironic attitude toward her own nostalgia: she knows that there is no turning back. Having been given a sexual license, she knows from personal experience that sexual repression is not the source of all human misery, and that unlimited sex will not solve all (or perhaps any) of our problems.

Last Night in Paradise is not an easy book to categorize. One is alternately repelled by the author's narrow Upper East Side provincialism and attracted by her hard-won personal insights into our current cultural quandaries about sex.

Imagine a bright, literary young woman -- raised with four sisters by a married feminist mom (author Anne Roiphe) in a Manhattan brownstone, spending her adolescence (like everyone else she knows) hanging out "in Sheep Meadow in Central Park in the middle of the night smoking pot, looking at the stars," getting smashed on cheap liquor, and sleeping with boys -- coming to grips, through sheerly personal reflection without assistance from any religious or moral tradition, with the question: What does sex mean?

In the Sixties sex was a thrillingly revolutionary act, a chance to vote with one's genitals for a new and better world. But soon sex with strangers became boringly bourgeois, a mere rite of passage for hip New York girls like Miss Roiphe, who by age 15 was "beginning to go to hotel bars and flirt with businessmen over whisky sours."

The attractiveness of AIDS, Miss Roiphe hazards, is that it gave back to sex what the Sixties stripped from it: consequences. If sex can kill you, then, at least, sleeping with someone means something. In some cases it may even mean you are willing to die for love.

Unprotected sex thus becomes the only illicit act, a metaphor (or a vehicle) for the experience of being swept away by love. Miss Roiphe points to a scene from a recent autobiographical movie, Savage Nights, acclaimed in France but panned by morally censorious American critics, in which an HIV-positive artist seduces a 17-year-old girl. She reaches down and tosses the condom away: "I want to share everything with you," the girl says huskily. "Even your disease."

It is not just bisexual French film directors afflicted with AIDS who feel the romance of unprotected sex. In a study of sex codes among inner-city white youths, the University of Pennsylvania's Patricia Stern notes that teens are unlikely to use condoms in steady relationships. "The most common reason for not using birth control among these youths," the scholar reports, "is that unprotected sex is a pledge of intimacy and trust which elevates 'f -- -- ' to 'making love."'

Miss Roiphe is puzzled by the deeply moralistic response from those American critics to the French lyricism of Savage Nights; she attributes it to our current cultural obsession with avoiding risk. "The message," she writes, "was not really one that we wanted to hear: true love is not concerned with self-protection."

Perhaps. But there is a deeper reason the French movie did not entirely translate: The idea that romantic love involves a yearning for death (as Denis de Rougemont pointed out in Love in the Western World) is an old European tradition. In America, the end of romantic love has always been marriage.

There are still Americans who believe in this happy union of eros and domesticity. Miss Roiphe describes her lunch with a 26-year-old staffer for Concerned Women for America, a "secondary virgin" who after a few college flings has now determined to wait until marriage:

I search her face for signs of regret. There are none. Christine's faith in the future is unlimited. She has turned her back on a world of divorce and affairs, sudden flashes of desire, instant passion . . . and the whole precarious and anarchic pursuit of pleasure. In its place she has something else: a sublime confidence in her reward. "God hasn't yet given me that special guy," she says, mixing King James with Cosmopolitan, but she is certain that He will.

Well, maybe He will or maybe He won't. God doesn't always send you what you think you want. The task of reconciling one's actual life with one's youthful dreams can be daunting.

But faced with Christine's decision to put her faith in love, Miss Roiphe admits, "I find myself infuriated. I suddenly want to convert her more desperately than she wants to convert me, although there are definitely times when I wish that, like Christine, I had a giant book that would tell me how to live my life instead of a copy of Elle to tell me how to kiss, Anna Karenina to tell me not to cheat on my husband, and a John Updike paperback to tell me how to go about it if I do."

"What could be wrong with freedom?" Miss Roiphe asks. "It's not the absence of rules exactly, the dizzying sense that we can do whatever we want, but the sudden realization that nothing we do matters."

That is a brilliant epitaph for the sexual revolution, and for the whole Sixties cult that tried to find meaning in the breaking of taboos. After the last taboo shatters, then what? But for the Katie Roiphes of the world, alas, there is no retreat, and no clear way of moving forward either. In the end Miss Roiphe is left with only the sad awareness of "how much we long for moral clarity and how impossible it is for us to have it."