The French director Andre Techine is a master at evoking personality quirks, the unpredictability of relationships and the haphazard way love affairs, friendships and social groups form and dissolve. Many of his films, like "Changing Times" and "Wild Reeds," portray a multicultural environment in which French and North African characters mingle, sometimes uneasily.

His films are also casually sensual. The fluid sexuality of at least one male character in most Techine films is almost a given; the director's strong, free-spirited women are in charge of their own sexuality to a degree rarely found in American movies, unless those women are designated as vixens. But if the world according to Techine is a liberated wonderland with few boundaries, living there comfortably requires that you wear sophisticated psychological armor.

His newest film, "The Witnesses," set in 1984, observes this wonderland shocked out of its complacency by the arrival of AIDS. Suddenly a closely knit group of friends -- straight, gay and bisexual -- is forced to confront the uncertainties and terrors of the epidemic in its early days. It is imperative that they disclose their discreetly kept sexual secrets and report their HIV status.

This story of paradise lost begins with a domestic spat in the Paris residence of a handsome couple: Sarah (Emmanuelle Beart), a well-to-do writer of children's books, and her working-class husband, Mehdi (Sami Bouajila), a hard-nosed police inspector of North African descent. Mehdi is outraged at Sarah's indifference to their newborn baby, whose cries she tunes out with earplugs while she works. Sarah and Mehdi have a pact: Both are allowed to take outside lovers in a "don't ask, don't tell" arrangement that seems to work, although it is not without its subliminal tensions.

Meanwhile, Sarah's close friend Adrien (Michel Blanc), a homely, middle-aged gay doctor, prowls a popular cruising ground, where he meets Manu (Johan Libereau), an arrogant young man who refuses to sleep with him but agrees to be his companion and his student of life's finer things. Wildly in love with his shallow, narcissistic protege, Adrien is shrewd enough not to push too hard, but there is an element of masochism in his abject devotion.

This beautifully acted ensemble film, which uses recurrent images of water and aviation, unfolds in three chapters. The first remembers the heady pre-AIDS era. The second observes the foursome's reactions to the crisis, which for each is a test of character and of the strength of bonds they have taken for granted. In the third, those who remain pick up the pieces and go on.

"The Witnesses" (in French with English subtitles), which opens Monday at Pittsburgh Filmmakers' Harris Theater, Downtown, sidesteps most of its opportunities for high drama, political sermonizing and the jerking of tears. Techine, working from a screenplay he wrote with Laurent Guyot and Viviane Zingg, refuses to pigeonhole his characters in comfortable niches or ethical positions. The film skips ahead with the pace of a light romantic comedy, rarely lingering long enough on a scene to conjure melodrama.

"The Witnesses" may frustrate those who prefer movies that tell clear-cut stories in which hard lessons are learned. But in the director's farsighted vision of life, the ground under our feet is always shifting. As time pulls us forward, the shocks of the past are absorbed and the pain recedes. In its light-handed way, "The Witnesses" is profound.

Opens Monday at Harris Theater.'The Witnesses'

Starring: Michel Blanc, Emmanuelle Beart, Sami Bouajila, Julie Depardieu, Johan Libereau.

Rating: Not rated but R in nature; includes sexual content.