'Walk Proud" continues the downward spiral of the youth gang melodrama trend. Amazing as it seems, the outrageously unrealistic "The Warriors" has yet to be improved on.

Pompously titled and doggedly conventional, "Walk Proud" even falls short of "Boulevard Nights," an earlier failed attempt at a naturalistic story set in the Mexican American communities of Los Angeles.

A pallid Romeo & Juliet story about teen-age sweethearts from opposite sides of the tracks - a Chicano boy impersonated by Robby Benson and an upper-middle-class Anglo girl played by Sarah Holcomb-"Walk Proud" falls back on the spongy uplift that was guaranteed to provoke derision from teen-agers a generation ago and should do the same today.

Ironically, the 1953 movie version of Evan Hunter's "Blackboard Jungle" would probably have more contemporary appeal than "Walk Proud," a supposedly up-to-date original written by Hunter. The stilted dialogue makes you wonder if Hunter did his research by watching all the misunderstood-kid movies of the '50s. Fed up with the evasions of the bad boys he's trying to help, a Chicano youth worker exclaims, "Sometimes you guys make me sick, you know that?" Defying his gang leader at last in order to make a fresh start with his respectable steady, Benson sagely inquires, "Where does it end, Cesar?"

If you encounter this rhetoric after spending an agonizingly authentic hour or two with one of the recent TV documentaries about juvenile offenders, you feel weirdly disoriented hearing such liberal quainttalk emanating fron the barrio. "Walk Proud" blunders around inside a self-inflicted authenticity gap.

Benson inspired some hostility when it was first announced that he'd be playing a Chicano lead. Although Benson is woefully inadequate in almost every respect, he doesn't deserve the blame for the fundamental mawkishness of the picture. At least he still looks a juvenile, which is more than one can say for most of the gang members. As the pugnacious Cesar, Pepe Serna adds insult to injury, imposing a bombastic performance on a slightly over-age presence.

There are enough examples of hesitant or obtrusive acting to suggest that Robert Collins is a director of limited experience or questionable vigilance. Despite the obligatory gang violence, "Walk Proud" is astonishingly stuffy. An inordinate amount of dramatic business is conducted by somebody-told-me-so ruses like the following snatch of dialogue, addressed to the hero by the heroine: "You belong to a gang, Emilio. I asked Carl in my English class."

Emilio gets an elaborate show down with his alienated gang cronies, who customarily beat up turncoats when they leave the fraternity. Having it both ways, Benson's Emilio punched out Cesar before dutifully running the gantlet and enduring a traditional punch-out himself. One surmises that this sequence of events makes Emilio doubly honorable, or perhaps curiously stupid.

I suspect that Benson had a hand in shaping this well-beaten denouncement. Early in the film his character hopefully asks, "Do you think I look like Marlon Brando?" The battered yet battling Emilio is obviously calculated to recall the conclusion of "On the Waterfront." All the homage needs to be complete is a friendly priest murmuring "Cesar says you can't stand up" into his ear before Emilio staggers to his feet and trudges off to a brighter tomorrow.

hat rosy future is anticipated all too optimistically on the soundtrack, as Benson himself warbles a twerpy exit song called "Adios, Yesterday." If ever a movie had too much yesterday, it's "Walk Proud." CAPTION: Picture, Robby Benson