By the time this troupe is through with Moliere . . .; Le Bourgeois Avant-Garde. A comedy after Moliere, written and directed by Charles Ludlam for the Ridiculous Theatrical Company.

Such notables as Fielding and Dryden are among the authors directly influenced by Moliere. Now add Charles Ludlam - whose latest farce takes ''Le Bourgeois Gentilhomme,'' runs it through a blender, and tosses the scrambled result cheerfully in our laps. Sound ridiculous? That's the point.

The hero of ''Le Bourgeois Avant-Garde'' is a Mr. Foufas, who rivals Moliere's ''would-be gentleman'' in his determination to be something he's not. A mere businessman until now, he's itching to fathom the latest artistic fads - which Ludlam considers even more preposterous than Foufas himself, and that's going some.

Ludlam heaps ridicule on Foufas's pretensions, but saves his big-time scorn for the avant-garde itself, which he feels is not only post-modern but post-talent. The often satirical characters range from an effete composer to a graffiti artist named Moderna 83, who speaks in words of one syllable - and it's always the same syllable.

Looking at Ludlam's apparent disdain for the avant-garde, you'd never know he has blazed a few trails himself as head of the Ridiculous Theatrical Company. Perhaps it's just posing and posturing that upset him, though he treats the whole ''vanguard'' scene with a withering attitude.

In on the plot are such Ridiculous regulars as Bill Vehr and Black-Eyed Susan , along with some energetic newcomers. Ludlam leads them with a typically frantic performance that strikes a dozen perfect notes for every occasional clinker.

In all, it's not a great evening with the Ridiculous gang - sometimes self-conscious about its own silliness, and childish in some of its vulgar touches, which would probably mandate a PG rating if this were a movie. Still, the plot is as thick as can be, and the satire is closer to uproarious than anything the troupe has done since ''Reverse Psychology'' a few seasons ago. Moliere will never be quite the same - and neither will the avant-garde, which has surely met its match.