An inconsistent but good-natured ramble, "Bustin' Loose" looks like a secure investment for Richard Pryor fans. One gathers from the credits, which list Pryor as the co-producer and indicate that he originated the story, tht Pryor may have enjoyed more authority over this vehicle than any of his previous movie projects. The miscellaneous ingredients -- self-contained comedy routines, a tentative romance with co-star Cicely Tyson, a juvenile contingent of eight supposedly troubled and unruly kids, occasional tear-jerking interludes and morale-building speeches -- presumably reveal the kind of mix he desires. The trick is to achieve a more coherent and satisfying blend.

Pryor plays a hard-luck Philadelphia crook whose failure to pull off a grand larceny scheme leaves him at the mercy of a parole officer, Robert Christian, whose fiancee, Tyson, is a schoolmarm anxious to resettle a group of handicapped and emotionally disturbed kids. Her school has lost its funding and rather than see the students moved to a ghetto alternative, Tyson resolves to take them out West, to a Washington farm owned by her aunt and uncle. Compelled to repair a broken-down schoolbus as a favor to Christian and Tyson, Pryor is soon pressed into service as the driver. The ensuing cross-country jaunt is conceived as an odyssey that will transform the disreputable hero from incorrigible loser into resourceful troubleshooter, responsible father figure and romantic catch.

The first feature directed by Oz Scott, the theater director best known for staging Ntosake Shange's "For Colored Girls . . .," "Bustin' Loose" looks crisply and attractively shot from scene to scene, but a good deal of detouring and tone-shifting seems to be going on between scenes. The sequences differ radically in tone and emphasis as the madcap Richard Pryor charges places with the sincere, heartwarming, speechmaking Richard Pryor or as the sputtering plot requires another push westward.

I'm not sure if the patchwork randomness of "Bustin' Loose" grew out of a screenwriting breakdown or if a story naturally tends to unravel when writers collaborate with a comic star who may be prone to mercurial moods and contradictory intentions. For example, it's no doubt important to Pryor that the kids in the story be kids with problems, but there's a huge discrepancy between the way they're exploited as comic foils one moment and objects of concern the next.

The romantic element is also inadequately documented. The basic chemistry, borrowed from "The African Queen," is sound enough, but the episodes necessary to bring the scroungy hero and the prim heroine into a plausible and satisfying intimacy never seem to have been written.

The best sustained comedy interludes are the opening larceny scam, in which Pryor gets expert support from Gary Goetzman, as a gullible liberal store manager and Luke Andreas as his suspicious, cynical leader, and an encounter with a party of Ku Kluxers whom Pryor contrives to disarm into white-robbed pussycats. A sequence that looks promising -- Pryor attempting a con on the con artists promoting a "dare to be rich" scheme -- degenerates into a prolonged fizzle.

Given Pryor's narrow brush with death last year, the fire motifs in the script are peculiarly creepy. One of the kids is supposedly prone to pyromania, and Pryor ends up with a comically blazing cap while trying to douse one of his spontaneous conflagrations. On another occasion Pryor forgets that he's stuck a lit cigar in bathrobe pocket. Coming on to Tyson, he confides, "You set me on fire." One doubts if any of these scenes would have survived if fate had been unkind and "Bustin' Loose" had turned out to be the last Richard Pryor movie.