Philippe Noiret moves through "My New Partner," an amiable if overlong action comedy, like a clumsily majestic walrus. With his hands glued in the pockets of his leather coat, his arms become flippers; his whiskers are walrus whiskers decorating a thing more snout than nose, and he has the same sloping, pear-shaped vastness. When he walks into seedy hotels, flea markets or the police station where he works, all fall into step behind him, adhering to his will, like minnows sucked into his wake.

Noiret plays Rene', a detective cheerfully acquiescing in the corruption around him. Rene' fleeces pimps, drug dealers and petty criminals, and wagers his graft on the trotters; he takes copious meals on the arm, in return for looking the other way when the restaurateur runs a crap game.

This comfortable setup is threatened when Rene' is assigned a new partner, Franc,ois (Thierry Lhermitte), a provincial prig fresh from the academy. Rene' reads the racing forms, Franc,ois the penal code; Rene' orders expensive Bordeaux, Franc,ois takes water. "We're going to have fun together," Rene' says, napkin-dabbing a mouth so sensual it seems to exceed the bounds of his own face. "I didn't join the force to have fun," Franc,ois replies.

"My New Partner" is a one-joke movie -- gradually, deliberately, Rene' brings Franc,ois over to his way of thinking, to the pleasures of prostitutes, the ponies and Cha teau Latour. But even the familiar slapstick ignites because of Noiret, imperturbably confident in the sinfulness of everyone around him -- he adds a silent "I told you so!" to every occurrence.

Lhermitte and the rest of the supporting cast, which includes chanteuse and nightclub owner Regine, are unexceptionable props in Noiret's one-man show. Julien Guiomar adds a nicely frenetic cameo as the Chief that recalls Herbert Lom's characterization in the "Pink Panther" series.

Director Claude Zidi has shot "My New Partner" clumsily, and for a French farce, there's a surprising shortage of sex. Still, buoyed by Noiret, it's a pleasant, melt-in-your-mouth madeleine of a movie. My New Partner, opening today at the K-B Janus, is rated R and contains some nudity, violence and sexual situations.