In Mo' Money, which he wrote and produced, Damon Wayans plays a petty urban crook who has grown sick of risking his butt for the sake of a $50 con job. Enticed by the luscious, upwardly mobile young woman (Stacey Dash) he sees entering a swank downtown office, he finagles himself a job in the mail room. The movie is fast and funny when it shows us an array of dysfunctional corporate types through the eyes of its incredulous hustler hero: We're seeing dorkishness at its most embarrassingly Caucasian. And Wayans, who on TV's In Living Color exaggerates and revels in the absurdity of black stereotypes with some of Eddie Murphy's old gusto, doesn't reserve his darts for whites. In Mo' Money, he lampoons the acquisitiveness of ghetto dreamers; he sees the comic underside of people who don't have anything but can still fantasize about having it all. After a while, though, the hero is lured into the clutches of a corrupt coworker (John Diehl), and the movie becomes a halfhearted ''thriller.'' It loses not merely its pulse but its comic attitude, its manic satirical vision of inner-city money fever.