"The Woman Next Door," a fresh ball of fluff from Francois Truffaut, purports to be the chronicle of a passion so intense that it leads to tragedy. The catch is that the mood of the film, which opened yesterday at the K-B Janus, is always too placid to support a drastic turn of events. The erotic temperature never creeps above tepid as this negligible account of desire glides across the screen.

Given the theme and the location -- a secluded suburb of Grenoble -- an amusing alternate title might be "Body Heat, French Style." The misadventure opens with an overhead panorama of a police van speeding to the scene of some emergency. Its destination is revealed at the fadeout, by which time the mystery has degenerated into morbid, unwitting slapstick.

In the meantime a narrator introduces herself: Veronique Silver as Odile, a middle-aged woman who manages a tennis club and restaurant in the community where the story unfolds. She emerges as a minor confidante of the ill-fated principal characters, but her authority appears to originate in symbolism. Odile is crippled, the result of a suicide attempt inspired by romantic despair years earlier. Truffaut imagines that this sadder-but-wiser survivor of an unhappy affair will enhance the pitiful fable to come with a poignant perspective.

Gerard Depardieu fares little better as the male component of this misalliance. His character, Bernard Coudray, appears to be a comfortable and contented young family man. Something begins to disturb him when a new couple, the Bauchards, rents the adjacent house and he's introduced to the wife, Mathilde, played by a striking new actress with a beguiling name, Fanny Ardant.

Bernard's discomfort is promptly explained when Mathilde seizes an opportunity to speak to him privately and we learn that they were once lovers. Evidently, a tempestuous affair was broken off about 10 years earlier. The awkwardness of the reunion seems decidedly more comic than ominous.

The effects Truffaut wants and what he gets couldn't be more contradictory. The idea is to establish an atmosphere of disarming bourgeois gentility and tranquility so that the eruption of hidden, uncontrollable impulses will seem especially shocking. But no deeply troubling emotions can begin to break through the breezy, attractive social facade.

Truffaut's misjudgment may be measured in the way details meant to be startling play funnier than details meant to be amusing. For example, there's a deft early sequence that depicts Bernard, unsettled by the sight of Mathilde at her window, absentmindedly locking himself out of his car one morning. Unfortunately, an interlude designed to take your breath away provokes a bigger laugh: Mathilde pulling a faint in the supermarket parking lot after Bernard kisses her for the first time in a decade.

Truffaut permits this swooning motif to repeat itself. Inevitably, the chuckles accumulate, too. Driving back from a tryst in the countryside, Ardant wears the same tearful, despondent expression she wore on the drive out. Indeed, Truffaut may have used the same take going and returning, inspired by a ludicrous vision of life's infinite capacity for ironic recurrence. During a party at the club a deteriorating Mathilde steals away to fling herself behind a hedge and shower the turf with tears. The pathetic effect is oddly undermined when Truffaut has the other guests trot out to gawk at her.

Literally lovesick, Mathilde spends some time in the hospital, threatening to waste away and then suddenly recovering, but Fanny Ardant looks the same from one phase to the next. Perhaps Ardant should avoid roles that trade on extravagant suffering, because her dark, angular visage grows less distinctive and appealing when clouding over. In a mischievous, humorous temper she looks eccentrically seductive, blessed with irregular features that might be expressive dynamite in comic roles -- a long sloping nose; a strong, slightly protruding jawline that combines with the nose to give her profile an amusing forwardness, like a ship's prow challenging the waves; and a wide, ravenous mouth that opens into a brilliant smile. One trusts that she'll survive a debut inclined to reduce her to a neurotic laughingstock.