The French, who don't like anybody very much, not even each other, understandably went bonkers for "Life Is a Long Quiet River." A sour little social diatribe by first-time filmmaker Etienne Chatiliez, this tale of two families, a nurse scorned and the gynecologist who done her wrong, wrong, wrong was a moneymaker that won four Cesars (French for Oscar).

Heretofore famed for making hamburger commercials, Chatiliez brings a salesman's cynicism to this harsh comedy of social mechanics and class rivalry. You can practically see him twisting his whiskers as he plays with the wretches caught up in this xenophobic thesis on what counts most in a child's upbringing -- heredity or environment? Never mind all those twin studies that indicate it's in our genes; Chatiliez says our fate is all in whether we are raised by porky Algerian layabouts or prim French bourgeois.

Written by Chatiliez and Florence Quentin, the story turns on the machinations of Josette (Catherine Hiegel), a nurse who decides to get even with her neglectful lover by switching two babies the lecherous old alcoholic has just delivered. Twelve years pass, Dr. Mavial (Daniel Gelin) has just lost his wife and Josette expects that he will marry her as promised. But at graveside, the malevolent Mavial says of his wife, "I will never be able to replace her." So Josette posts two letters -- one to the trashy Groseilles and the other to the proper Le Quesnoys.

The Le Quesnoys, a preposterously perfect family, are horrified to learn that their daughter, Bernadette (Valerie Lalande), is really inferior material and that their real son, Momo (Benoit Magimel), is a hard-drinking purse snatcher. They decide to adopt Momo and to hide the truth from Bernadette. The Groseilles agree to relinquish both children for a large sum of money, which they quickly spend on tacky outfits, junk food and hair-coloring products. Seeing their plight, Momo pawns his new family's silver and shares his newfound wealth with his old family.

One day Momo brings some of the repressed Le Quesnoy kids to visit the Groseilles, and the petite bourgeois are delighted with the carefree lifestyle of the uncouth immigrant family. The eldest son is seduced by the Groseilles' eldest daughter, a slut, and the others take to drinking beer. Inevitably, the Le Quesnoys are destroyed because "Momo can't escape the dirty, nasty habits he's picked up."

Except for Bernadette, who has a nervous breakdown when Momo tells her she was born of le pond scum, there are no sympathetic characters whatsoever. But there are some wonderfully insipid performances by Helene Vincent and Andre Wilms as Madame and Monsieur Le Quesnoy. Vincent, best known for her theatrical accomplishments, is ludicrous perfection as the ultimate French wife and busy mother, who spends her free time aiding a pop-singing priest with his church hootenannies.

The Groseilles are ethnic caricatures, greasy fatsos grossly played. Christine Pignet weighs in most prominently as Madame Groseille, a mole-faced Gallic tugboat with the dimensions of Roseanne Barr. Chatiliez and his colleagues leave no doubt about it, thin people make better parents. Civilization is buckling under the combined tonnage of overeating and bad manners. C'est si bonbon.

Life Is a Long Quiet River, in French with English subtitles, is playing at the Key and is not rated.