Now and then it is possible to observe the moral life in the process of revising itself.

THE LATE LITERARY critic Lionel Trilling spoke these words during a series of lectures he delivered at Harvard in the spring of 1970. And though the lectures happened to deal with centuries-old cultural developments, this process of moral revision is forever with us. One wonders whether, someday, similar words will not be said about Woody Allen's brilliant new movie Hannah and Her Sisters.

Flowing through the many moments of unparalleled humor and the familiar scenes of Allen's self-deprecation is an earnest message which few have made, either in the 1960s or the 1970s. That message celebrates neither the endless experimentation and rebellion of the one decade nor the untrammelled complacency of the other. Rather, the way in which the movie extols those homegrown verities that Hollywood has long patronized as bourgeois earns Hannah and Her Sisters its status as a cultural landmark.

To some, the film will appear the finely crafted comedy of an old master. And certainly there is no shortage of laughs. But the humor in Hannah and Her Sisters functions the same way that humor does in life; it cushions us in situations of discomfort.

STRIP AWAY THAT humor and one is left with a grim reality. As is, the movie is filled with an almost unrelenting--even unbearable--realism. For all his affection for that city of "people, traffic, and restaurants," Allen cannot conceal the fact that New York City can be a lonely place. It is a place of lonely singles who entrust their lives to doctors and analysts, where highbrow culture is merely an expensive distraction from ennui, and where material riches can not compensate for spiritual bankruptcy.

With the exceptions of Hannah (Mia Farrow) and her ex-husband Mickey (Woody Allen), none of the characters here can stake a claim to too much sympathy. Together they make up a collection of overgrown children. Hannah's husband Eliot (Michael Caine) longs for his wife's youngest sister (Barbara Hershey); her mother, an actress, is a boozy old flirt; her actor father is a vain failure, and rounding out this lot is Hannah's other sister, the cranky Holly (Diane Wiest).

During its first half, the movie revolves around Eliot and Lee's affair and Holly's manic moods. Mickey begins a desperate search for "the meaning of it all," after a false alarm that he has cancer gives him an intimation of mortality. It is a world of petty vices like alcohol and cocaine. In the hierarchy of values, sexual pleasure ranks above marital fidelity and sibling loyalty.

In Eliot and Mickey we find the familiar polar character types who, between them, have recently come to dominate serious fiction and film. Eliot struggles under the romantic illusion that absolute fulfillment can be our lot on this earth. He mistakes his fleeting moments of passion with Lee as promise of perfect happiness and in so doing threatens a good--and much more lasting--relationship. Mickey, the nihilist on the other extreme, erroneously concludes that because life ends it must therefore be meaningless.

BUT THIS IS a Woody Allen story. Just when we've arrived at the brink of despair, all losses are restored and all sorrows end. Eliot and Lee's affair ends; Mickey recoils from the thought of suicide and rebounds exuberantly; and the three sisters settle down to happy marriages. People learn to distinguish between lust, which is momentary, and love, which is something stronger and longer lasting. They understand that the self-centered life is a dead end. And they realize that in this world, since a whole life is impossible, they might as well settle for a half.

Twenty years ago we had The Graduate in which a confused young man has an affair with the mother of the woman with whom he eventually elopes. Just two years ago we had Robert De Niro and Meryl Streep in Falling in Love which turned The Scarlet Letter on its head and told us that adultery is a-okay.

With Hannah and Her Sisters, though, the hedonistic impulse that has driven the arts both high and low for more than two decades appears to be at long last exhausted. Hannah and Her Sisters runs against the modern sensibility by suggesting that faith, family and community augment--rather than compromise--our freedom and happiness. It steers the difficult course between the tempting pitfalls of romanticism and nihilism--sentiments, or sirens, which have received too much for too long. The film asks us--in the unabashed words of the song Holly sings--to "be old fashioned with me."