"Fast Times at Ridgemont High" is a rather pedestrian realization of Cameron Crowe's same-name book, which is little more than vignettes hung together within the frame of a school year. Crowe has been faithful in rendering the rituals of adolescence in his own screenplay, but he accents the most obvious aspects -- sex that's more talk than action, peer-group pressures and, to a much lesser degree, drugs -- even more than he did in the book. It's an uninspired blend, integrating the boys from "Porky's" and the girls from "Foxes" into a vehicle resembling the worst of "American Graffiti" and the best of "Rock and Roll High School."

Since there is no plot per se, the weight falls on the young cast, and for the most part they cannot carry the film. One never reaches a point of involvement with any of the major characters, who troop across the screen as if they were being let out of assembly.

Director Amy Heckerling seems to have miscalculated; if you haven't read the book, it's going to take most of "Ridgemont's" 92 minutes to figure out who's who. The types may be familiar, but the interplay is confusing. It's almost as if Heckerling decided to direct the film for a wholly adolescent audience with television expectations and reared on quick cuts, non-linear development and puerile dialogue.

The most convincing and accessible character is Sean Penn's long-haired, molasses-mouthed, drug-dazed Jeff Spiccoli, Ridgemont's resident surfer-doper who walks, permanently out of step, under a cloud of his own making. Penn, seen recently as Timothy Hutton's roommate in "Taps," has marvelously elastic features and brilliantly captures a particular kind of outlaw adolescent. "Ridgemont" comes to life only through his comic relief.

Judge Reinhold, who portrays the ambitious Brad Hamilton, prince of the fast-food hierarchy, is a WASP-ish version of the Boogie character in "Diner": Reinhold even resembles Mickey Rourke -- he's a bit taller, but just as hound-eyed and quizzical, the hustler who almost always comes up a loser. Because of shortcuts, one never senses how important Brad's fast-food jobs are to his self-image, a major point in the book. In the film, he comes across as a petulant preener who could care less whether he's at Hamburger Heaven or Captain Hook's Fish and Chips.

Robert Romanus as Mike Damone, or "Mr. Attitude," and Brian Backer as Mark "Rat" Ratner are stereotypes who owe their all to "Kotter" and Woody Allen, respectively. Veteran Ray Walston puts in a sincere cameo as Mr. Hand, the history teacher who likes to call out grades as he hands out test papers. Most everyone else is so minor it's hard to match screen credits to names (try to figure out just who Pamela Springsteen plays; probably only she and brother Bruce know).

The Ridgemont girls, Stacy Hamilton and Linda Barrett in particular, dominate the book; in the film the roles have been reversed. Barrett, played by the winsome Phoebe Cates, has been all but written out of the film, though not enough to invalidate a brief topless appearance in one of Brad's weakly realized fantasies. At least she and Hamilton, played by Jennifer Jason Leigh, are real teen-agers; most of the boys are men and look it. Leigh plays Stacy with such cardboard passivity that it's hard to care what happens to her, a damning quality since she's the catalyst for almost everything that happens in the film.

The dialogue sounds like sitcom one-liners, from Brad's "I shall serve no fries before their time" to Linda's rebuke to Stacy: "We can't even get cable here and you want romance?" Much of the film was shot at the Sherman Oaks Galleria mall, but even that is a weak prop; the definitive use of a mall still rests in the hands of director George Romero and his "Dawn of the Dead."

Outside of Spiccoli, there's no drug abuse in "Ridgemont," no drinking, not even any smoking; there are pointless dribbles of profanity, and selective nudity. (Leigh apparently drew the short straw -- she disrobes twice.) There's even a "Graffiti"-like epilogue that catches the audience up with the main characters. At best, "Ridgemont" is drive-in fodder for high-school kids who don't care what's on the screen.