"Jupiter's Thigh," opening today at the K-B Janus, is a dismaying reminder that Hollywood filmmakers don't have a monopoly on crass, nest-fouling miscalculations. A sequel to the charming, expert romantic comedy-mystery "Dear Inspector," it reunites the original co-stars, Annie Girardot and Philippe Noiret, with the original director, Philippe de Broca, and screenwriter, Michel Audiard. The lamentable results suggest that their first association may have been a happy accident.

It's conceivable that experienced filmmakers may not appreciate what it was that made their hits ingratiating in the first place. "Jupiter's Thigh" cannibalizes a successful formula even more recklessly than "Smokey and the Bandit II," "Rocky II" and "Superman II," all of which probably pay a price in public trust concealed by their immediate box-office returns.

The most damaging indulgence in "Jupiter's Thigh" is the trivialization of the leading characters. Girardot and Noiret recreate their original roles as Lise Tanquerelle, a Parisian homicide detective, and Antoine Lemercier, a professor of Greek at the Sorbonne, but the reunion is ruined by facetious contrivances. Initially a delightful match, they're now compelled to behave in ways that degrade the characters we were drawn to. In "Dear Inspector" Lise and Antoine were absent-minded but smart and conscientious middle-aged professional people. In "Jupiter's Thigh" they become frantic, scatterbrained buffoons.

This ill-conceived switch demands that the characters, now married and embarked on a honeymoon in Greece, make a mockery of their professional standards. It's as if Lise had gone on holiday expressly to break the laws of a foreign country, while Antoine was going out of his way to endanger relics of Greek antiquity.

The depressing runaround commences when Antoine is challenged by a young archeologist, Hubert Potard (Francis Perrin), while pontificating on the glories of Greece for Lise's edification. The rival scholars patch up their dispute over drinks that evening, but the Lemerciers discover a new source of conflict in their new acquaintance -- Hubert seems to be estranged from his beautiful young wife, Agnes (Catherine Alric, the Catherine Deneuve look-alike who made a mouth-watering debut in "Dear Inspector"). Indeed, Agnes seems to be consorting with a Greek sailor, who soon provokes another crisis by disappearing with the prize relic unearthed by Hubert, a fragment of an ancient statue.

Continuing their trip, the Lemerciers stop the thief in Corinth and notify Hubert. The abashed Potards arrive to join the pursuit, which hits a fresh snag when Antoine and Hubert stumble upon the warm corpse of the thief and protest their innocence in vain to the Greek constabulary. The two French couples become outlaws, scurrying around the country chasing the real culprits.

French chauvinism, the granddaddy of chauvinisms, appears to account for the needlessly contemptuous portrayal of the Greek authorities. It would make more sense, of course, if Lise's professional standing made it easier for her to get Antoine out of the soup and work in harmony with the police in their host country. For some reason it has pleased de Broca and Audiard to depict the Greeks as provincial clucks who merit no consideration whatever.

Perhaps there's some perverse satisfaction to be derived from watching French tourists behave worse than any American yahoos ever inflicted on foreign soil. The Greek locations may also be divorced from the uses they're put to and enjoyed for gratuitous scenic satisfaction. Still, it's impossible to believe that fleeting scenic appeal can compensate for the human advantages de Broca and Audiard have thrown away. Lise and Antoine promised to be an endearing French variation on Nick and Nora Charles. Now they've tumbled somewhere south of The Ropers.