* Historically, most film portrayals of children and adolescents are phony from start to finish. When there is an exception to this, it often deals with negative aspects of young life. For a recent example, there was the grimly excellent British movie ''Bloody Kids,'' by Stephen Frears, which hit hardly a false note in its depiction of purposeless youngsters turning to destructive outlets.
Now there's an American film called Over the Edge that focuses on a similar subject. The film, directed by Jonathan Kaplan from a screenplay by Charles Haas and Tim Hunter, has a cautionary plot taking place in a ''planned community'' whose planners have neglected the fact that much of the population is 15 years old or under. The only place for the kids to hang out is an uninviting ''recreation center'' with a few pool tables. Since this quickly becomes tedious , and since the ''bad'' kids are lumped there with the ''good'' ones, mischief occasionally brews -- and the community hollers for the center to be shut down.
In detailing this sad situation, replete with occasional vulgarity and references to drug use, the movie is ruefully convincing. Near the end, though, ''Over the Edge'' goes over the edge itself, as the kids take an apocalyptic revenge on their unfeeling town. And the finale is a cop-out in the most cowardly Hollywood tradition. Still, while the filmmakers can't quite sustain their vision, they make a lot of darkly telling points about the real needs of young people and the good intentions that simply aren't enough for adults to offer. Filmed with a rock-and-roll energy that never quite lapses into recklessness, ''Over the Edge'' is a flawed but memorable movie.
Incidentally, its own history is as unusual as its story. Director Kaplan earned a deservedly high reputation a few years ago with a truck-driving melodrama called ''White Line Fever.'' On its strength, he was invited to make a big-budget Hollywood adventure called ''Mr. Billion,'' which was a failure on every level from the artistic to the financial. Back on the movie industry's poverty row, he has again shown his talent in ''Over the Edge,'' but its own studio declined to release it. After languishing on the shelf for a while, it had a limited showing at Joseph Papp's Public Theater in New York, where it garnered some rave reviews that parlayed the short run into a regular engagement at a real movie house - ironically the Cinema 3, an elegant and very un-''Over the Edge''-like theater in the Plaza Hotel. If its popularity holds up, it should be visible shortly in cities everywhere, a true success story, albeit an unexpected one.