It's the rare movie from Quebec that ever reaches commerical theaters in the United States. "Les Bons Debarras," or "Good Riddance," which opens exclusively today at the K-B Janus, is the first French-Canadian feature to play in Washington since Claude Jutra's "Kamouraska" six years ago.

The novelty is enchanced by a setting of exotic impoverishment: The characters dwell on the edge of squalor in a small rural community in the Laurentian Mountains. It's a bit like the milieu of a Faulkner or Erskine Caldwell novel transposed to the present in a foreign language. In addition, the name of the director evokes a royal family of Hollywood. "Good Riddance" is the third feature of 36-year-old Francis Mankiewicz, who turns out to be a French-Canadian nephew of the illustious Herman J. and Jospeh L. He also shows skill and intelligence, especially when it comes to using actors and settings expressively.

Unfortunately, "Good Riddance" also exposes a disappointing side. An intriguing downer, the movie deals with a compelling domestic conflict that goes begging for an effective story. The premise and the leading players elicit apprehensive human interest, but screenwriter Rejean Ducharme seems to be stuck for convincing plot twists and resolutions.

The conflict is provoked by the emotional turmoil in an 11-year-old girl named Manon, portrayed by an extraordnary juvenile actress, Charlotte Laurier. "With those little eyes you could cause an accident," remarks a character early in the film, foreshadowing Maon's destructive jealous behavior with rather transparent casualness. Nevertheless, Laurier's dark eyes certainly loom large pictorially. They flash with menancing brillance beneath shaggy bangs and provide vivid early warning signs of a stormy, devious temperament.

Manon, an illegitmate child, lives with her hard-pressed but resilient and generous mother, Michelle (Marie Tifo), who is determined to provide for both her daughter and her brother, Guy (Germain Houde), a mentally retarded adult whose behavior is becoming increasingly erratic. The family residence is a spare but comfortabe prefab shack in the country, from which Michelle operates the business that keeps them going: the cutting and delivering of firewood to affluent residents of the region.

Bitter about their social disadvantage and her mother's divided loyalties, Manon strikes out in ways impulsively calculated to give her a monopoly on Michelle's attention. A series of delinquencies and spiteful schemes appear designed to make Michelle feel guilty while making rivals -- notably her pathetic uncle and her mother's amirable finance, a middle-aged cop named Maurice (Roger Lebel) - feel unwelcome. Eventually, the girl resorts to lies and outbursts that supposedly force Maurice and Guy totally out of the picture.

"Good Riddance" presents a case history of a "bad seed" in which the motives of the malicious child are in no way supernatural or inexplicable. Manon acts out of a jealous, possessive need that is meant to seem scarier by virtue of its psychological clarity and authenticity. Her behavior is exaggerated to some extent by romantic literature -- she's passionately devoted to "Wuthering Heights" and fantasizes her mother and herself as in separable soulmates.

The movie goes astray trying to weave a believable plot around Manon's all too believable maliciousness. At each crucial juncture the story breaks down. For example, the lie Manon tells in an effort to discredit Maurice seems outrageous. There's no reason beyond storytelling convenience for Michelle to believe it, especially given the child's pattern of treachery. In addition, there's already a more formidable source of conflict: Pregnant again, the gusty Michelle is determined to keep the child, which Maurice would prefer to have aborted.

Manon's maneuvers against Guy also seem poorly contrived, in part because he's been introduced as a helpless wretch teetering on the edge of self-destruction. Her simmering hatred of him, which erupts in remarks such as "I'm fed up with morons," is really more distrubing. You can't totally dissociate yourself from this kind of spite, because the movie also acknowledges the fact that Guy is burden. Not even the exceptionally patient Michelle can deal with him in certain situations.

The movie is at its most effective when portraying the sort of desperate situation in which family emotions can be rubbed raw. Manon certainly has her reasons for acting like a little monster, but none excuse her from the moral implications of the questions of the question asked in weary perplexity by her mother. "Why are you so heartless?" Although the movie hits the skids in the course of examining a lower-depths family conflict, that question continues to reverberate.