Baby, It's You," a romantic third film by John Sayles, offers a touch of caste. It pairs sexy up-and-comer Vincent Spano, as a sidewalk sheik, and slight, fresh Rosanna Arquette, as an American princess.

The chemistry is not so much oil and water as grease and chicken soup, as the Trenton High tough tries his slick charms on his nice Jewish classmate.

Spano, now also costarring in "The Return of the Black Stallion," turned down "The Outsiders," another lower-meets-middle- class film, to create his sharkskin Sheik. His style and energy surge through the film in exciting contrast to Arquette's mannered but sometimes explosive performance.

As Jill Rosen, Arquette (recently of TV's "The Executioner's Song") masks her ragged need for Sheik behind snappish coquetry. She's an aspiring actress, but she's got no soul. She finds it with her Great American Greaser, who's bigger-hearted in his way than she'll ever be. And, of course, she finds herself, too. After all, this is a film about the '60s.

Theirs is a hurts-so-good affair that's going nowhere, but they can't seem to end it. And Sayles, as both director and writer, can't seem to break their clinches, either. He's best when he's close-up on the couple's tender love scenes or angry confrontations, but gets lost in a crowd scene. When Jill travels with her gaggle of girlfriends the pace falters, and it feels phony in this documentary-style film. And then we get into some extraneous territory when one girl slashes her wrists on prom night in a fit of guilt over being a loose woman.

Sayles tracks Jill more vigorously, leaving Sheik alone in Miami to pursue a career as the next Frank Sinatra. Sayles follows Jill from her 1967 high-school graduation to Sarah Lawrence, where she quails at learning the preppy way of knowledge. This allows Sayles to play campus historian, cramming his film with like-it-was trivia. He has a magnificent memory for detail and the film shows it, with only a few anachronistic glitches such as some of the songs.

Out of a budget of less than $3 million -- big bucks for a Sayles film -- a handsome chunk went for the nostalgic soundtrack, as integral to the film as the score is to an opera. The music refuels the movie, almost serving as dialogue. Purists are going to ask what Bruce Springsteen's work is doing in there, but it's not a big distraction. The sound is super throughout, from the Shirelles to Paul Simon to Sinatra.

And the lyrics "things turned out so right for strangers in the night" are the closest we come to denouement: We'll never know exactly what happened as we pan away from our star-crossed couple. Sayles leaves us a little in the dark -- he likes it that way, judging from his use of low lighting. And he likes it slow, because, like the '60s, he's laid- back. His work is an acquired taste, like Campari: bittersweet but worth trying. BABY, IT'S YOU, At the Cerberus.