'RIDGEMONT HIGH'

CAN there be anything about life in high school, particularly life in a suburban California high school, that the movie-going public hasn't already seen? Well, maybe there can. A little bit of it turns up in ''Fast Times at Ridgemont High,'' a jumbled but appealing teen-age comedy with something of a fresh perspective on the subject. ''Fast Times at Ridgemont High'' opens today at the Gemini and other theaters.

Cameron Crowe, who wrote the screenplay and the book on which it's based, spent a year masquerading as a high school student, making some very funny, believable notes on how his new friends really felt and sounded. Mr. Crowe chose to leave himself out of the resultant book, which didn't hurt it at all; questions about how he could know what had been said in a place like the girls' bathroom were rendered beside the point by the witty tone of his stories and by the ways in which they rang true. Amy Heckerling's film has no chief character either, and in this case it's more of a problem. The movie didn't necessarily need a reporter in it, but it needed a more distinct center than it has.

''Fast Times at Ridgemont High'' begins not at high school but at a shopping mall. That's where most of the kids spend their time, and an amazing number of them seem to work in fast-food restaurants. There is Brad (Judge Reinhold), who declares, ''I shall serve no fries before their time.'' There's Brad's sister, Stacy (Jennifer Jason Leigh), who complains petulantly to her friend and co-waitress, Linda (Phoebe Cates), ''You're the one who told me I was gonna get a boyfriend at the mall.'' There's Mark (Brian Backer), who pines for Stacy from afar or at least from the movie theater across the way, where he works as an usher. And there's Mark's friend Mike Damone (Robert Romanus), who gives Mark lots of free advice about how to handle women. To demonstrate some of this, Mr. Damone stops at the mall's record store and tries out some of his best lines on a lifesize cardboard cutout of Debbie Harry. He particularly stresses the aphrodisiac qualities of ''Led Zeppelin IV.''

All these young actors are relaxed, funny and natural. But the movie's real scene stealer is Sean Penn, as a pink-eyed surfer named Jeff Spicoli who wouldn't dream of holding down a job. Spicoli's dream is to describe surfing to a television interviewer as ''a way of looking at that wave and saying 'Hey, Bud, let's party.' '' Spicoli thinks nothing of ordering a pizza delivered to his history classroom, though his teacher, Mr. Hand, doesn't take it that easily. Mr. Hand (Ray Walston) is so bothered by Spicoli's truancy that he sends other students out to catch him in the hallways. ''You're wrong,'' yells Spicoli confusedly after he's been lured into the classroom on one such occasion. ''There's no birthday party for me in here!''

When the movie captures the awful sound of a high school band imitating the Eagles at a prom or the spectacle of two fast-food workers discussing their companies' secret sauces (one is ketchup plus mayonnaise, the other is Russian dressing), it's onto something that is both amusing and real. And Miss Heckerling sounds this note often enough to make her film both worthwhile and disappointing simultaneously. There's a lot to make her film likable, but not much to hold it together.

Mr. Crowe's book, notwithstanding its amiably light tone, has a certain amount of grit; it has its share of deaths, drug problems and other bleak moments, including one young girl's vividly recalled abortion. Miss Heckerling's film, before being cut down to its present R-rated form, reportedly contained that abortion scene and some explicit sexual episodes. Her film can do just as well without them, since most of it is too fluffy and insubstantial to accommodate anything raw. There's evidence here that she was after something other than a cheerful, casually diverting movie, but she hasn't achieved much more.