Falling well short of total tubularity, "Valley Girl" joins that lengthening list of summer comedies too trifling to reward much in the way of idle curiosity, not to mention anything resembling serious critical indignation.

On the relevant scale of comparison, this sexploitation comedy about the romance between high school kids from the opposite side of the Los Angeles hills--Julie, a nice, sunny suburban girl from the San Fernando Valley, and Randy, an ever-so-slightly punkish boy from slummy Hollywood--doesn't belong in the same league with "Fast Times at Ridgemont High" or "Baby It's You," more or less holds its own with "My Tutor" and "Porky's II" and never descends into the facetious pits with "Spring Break."

The names of the principal characters, attractively played by Deborah Foreman and Nicolas Cage as far as the superficial, threadbare material allows, provide a clue to the fact that screenwriters Andrew Lane and Wayne Crawford have borrowed their situation from "Romeo and Juliet." In this case the pressure that supposedly threatens true infatuation across class lines is identified as the disapproval of the heroine's girlfriends. Dramatically, the pressure never begins to register. The self-evident punk in Julie's life is her estranged boyfriend Tommy (Michael Bowen), a vain creep of a high school jock who treats her contemptibly and puts the make on one of her girlfriends (played by the diminutive dynamo Elizabeth Daily, who was the lead in "Street Music") on the rebound. Why Julie's set should be particularly offended by Randy, sort of a charming mutt of an ill-defined prole whose only punkish attribute is a slightly absurd hairstyle, and keenly solicitous about obnoxious Tommy is a prejudice that obviously cries out for, like, you know, elucidation.

As a matter of fact, it becomes pathetically apparent that the writers have depended on random borrowings from "Romeo and Juliet," "The Graduate" and "Grease" to keep their plot sputtering along. The quality of social observation in the script is consistently trite and trumped-up. The alleged class divisions between kids from different areas of the sprawling L.A. megalopolis don't amount to a hill of beans. There's not a single scene dealing with Randy's home or high school, for instance, so you're never sure where he's meant to emerge from socially. Perhaps he was an ethnic in some earlier draft that got blurred into terminal vagueness.

Julie is identified as the sensible only child of a comic relief mismatch, crisp Frederic Forrest and lugubrious Colleen Camp, as mellowed-out survivors of the counterculture who now run a health food restaurant in the valley. I suppose there was the prospect of something fresh in this notion at one time or another, but as exploited here, the residual hipster parents are typical sitcom clowns. Obliged to scramble with defective, amateurish writing, director Martha Coolidge scarcely has the opportunity to reveal much flair or assurance, but she treats the young cast members with an affection and consideration that permits fleeting moments of funny, appealing rapport. In her fragmentary debut feature, "Not a Pretty Picture," Coolidge demonstrated a knack for reproducing the tone and tensions of youthful dating rituals, and some of that knack is evident in "Valley Girl" despite the facetious inadequacies and indomitable simplemindedness of the script.

The production itself appears pinched and slapdash, so under the circumstances it represents a small miracle of either promotion or marginal charm that the movie has enjoyed a modest commercial success to date. The sound levels in particular need some cleaning up, because the rock numbers in the background frequently obliterate the babble of dialogue in the foreground. While it's not quite the novelty the filmmakers must have hoped it would be at one time, the girls' chatter makes a far more amusing and amiable racket. There's even an occasional inspired coinage, like "totally perpendicular," which I think is meant to be complimentary. VALLEY GIRL

Directed by Martha Coolidge; executive producers, Tom Coleman and Michael Rosenblatt; written by Wayne Crawford and Andy Lane. Produced by Atlantic Releasing. Rated R; 95 minutes. THE CAST Julie . . . . Deborah Foreman Randy . . . . Nicolas Cage