NOW THAT Andy Warhol's gone, John Baldessari may be the best guy to blame for the tiresome triviality of so much contemporary art.

The Hirshhorn, which has just opened a major Baldessari retrospective, credits the Californian with being a leading influence in American art. Another way to put it is that, as a hugely successful practitioner and teacher, he's a major contributor to the delinquency of minor artists.

But you can't stay mad at Baldessari as you go through this huge exhibition. His multimedia imagery and pseudosculptures are irritating and engaging by turns. Pontification alternates with wry self-awareness, dreary posturing with deadly wit, preaching with prancing, fussiness with farce.

Baldessari, 59, started out as a painter. But in July 1970 he took 13 years' worth of canvases to a San Diego crematorium and reduced them to a hatful of ashes he keeps in a book-shaped bronze urn. Just think, it coulda become a movement.

The following year Baldessari's new direction became clear. He made a half-hour videotape of himself writing, again and again, "I will not make any more boring art." You sit there and laugh and cry. But you don't leave.

He did a series of dumb landscape constructions called "California Map Project, Part I" (1969) in which each of the letters of the state's name is marked out on the ground with string or rocks or whatever, in various locations around the state. Photographs of them constitute the work of art. Yawn.

He uses stills from old movies and TV shows to create drab storyboards that tell no stories. He uses endlessly repeated images of excruciating ordinariness to create agonizing ennui. He goes on, on, on about nothing at all, all, all.

Yet, particularly in his earlier work, Baldessari keeps coming up with zany images and wry statements that disarm and delight. Many of his "paintings" contain only text, such as "Suppose it is true after all? WHAT THEN?" or "PURE BEAUTY" (both 1967).

In fact Baldessari's words are so much more interesting than his images that one wishes he'd burn some more of his stuff, and write by the light.

JOHN BALDESSARI: A Retrospective -- Through Jan. 6 at the Hirshhorn Museum and Sculpture Garden, Eighth and Independence NW. Open daily 10 to 5:30. Metro: L'Enfant Plaza.