Americans rarely see Jean-Paul Belmondo in the role of a farceur. As a matter of fact, only a handful of his movies, serious or frivolous, get imported in the first place.

So the sight of Belmondo facetiously scurrying about in "L'Incorrigible," constantly changing costumes, putting on false noses and mustaches -- even parading in drag during one sequence -- may seem diverting enough to justify interest in a basically expendable entertainment. Major expectations should definitely be checked at the door.

Opening yesterday at the West End Circle, "L'Incorrigible," which is about five years old, appears to have been negiligently improvised as a reunion vehicle at a time when neither Belmondo nor director Philippe de Broca had anything better to do and preferred to get in a light workout. Their association dates back to early New Wave hits like "That Man From Rio" and "Cartouche." It continues to this day. Unfortunately, "L'Incorrigible" seems to have been slapped together on an off-day.

Belmondo plays a flamboyant, irrepressible, essentially childish con man who resumes all his old dodges moments after being paroled. Genevieve Bujold is the social worker assigned to keep tabs on him. She resides with her parents at a private art museum whose principal treasure is a crucifixion triptych painted by El Greco. Papa happpens to be the museum's curator.

Belmondo wouldn't know an El Greco from an egg roll, but when his mentor, a semi-bohemian criminal esthete played by Julien Guiomar, learns of his connection, he sees the chance of a lifetime. Guiomar hatches an art-theft-for-ransom scheme that requires Belmondo's services as the inside man, cultivating and seducing the curator's daughter.

A feasible outline for romantice comedy exploitation, I suppose, but it hasn't been attractively contrived. On the contrary, the complications are resolved by making everyone shamelessly crooked. Belmondo's betrayal of Bujold is canceled out by her blithe willingness to betray her parents. There's as much double-crossing as you'd find in a classic film noir of the vintage of "Double Indemnity," "The Killers," "Out of the Past" and "Criss Cross." The breezy celebration of mercenary behavior seems closer to the tone of a Claude Lelouch caper comedy than a quality De Broca.

Nevertheless, De Broca's pictorial style is so deft and attractive that the movie is over and done with almost before the sour elements have an opportunity to leave their unpleasant aftertaste. "L'Incorrigible" is easy to watch and offers such incidential pleasures as Capucine (in an all-too-brief appearance as Belmondo's estranged girlfriend), an airy Georges Delerue score and awesome glimpses of Mont St. Michel. You just wouldn't want to take a snap quiz on the content five minutes after "L'Incorrigible" fades out. This picture presents the sort of charming front that can't withstand the slightest critical scrutiny.

A couple of years after "L'Incorrigible," De Broca and the same screenwriter, Michel Audiard, engineered the delightful "Tendre Pulet," known here as both "Dear Detective" and "Dear Inspector," for Annie Girardot and Philippe Noiret. (Incidentally, a sequel, roughly translatable as "Who Stole Jupiter's Leg?" should arrive later this year.) Would they have been as clever on behalf of Belmondo and Bujold back in 1975.