Juice: it means power, nerve, street-smart bravado, and according to Ernest R. Dickerson's new film it can definitely be had in oversupply. "Juice" is the story of how four young friends from Harlem are caught up in a murderous spree after one of them decides to test the limits of his machismo. The idea may be familiar, but the execution is much better than that, thanks to natural, affecting performances from the principals and a very sharp visual style. Mr. Dickerson, whose cinematography has been the reason Spike Lee's films look so good, has a terrific eye and some juice of his own. "Juice" begins with the innocent spectacle of Q (Omar Epps), Raheem (Khalil Kain), Steel (Jermaine Hopkins) and Bishop (Tupac Shakur) rolling out of their respective beds and heading off for school, which is a place they almost never see. Instead, they roam amiably through their neighborhood, engaging in such relatively innocent activities as shoplifting records and trading insults with rivals. Throughout this easygoing portion of the film, Mr. Dickerson (and his cinematographer, Larry Banks) gives the Harlem streets a rare crispness and clarity, and manages to position the camera in uncannily apt ways. The film's look is handsome but also claustrophobic, creating a caged feeling even in some of its outdoor scenes. Q, who is the story's relative straight-arrow (and who can't bear his given name, Quincy, since it suggests as much), stands a better chance than his friends of breaking out. Q has talents as a disk jockey, and he dreams of winning a Mixmaster Massacre contest at a local club, for which he has earnestly practiced on two turntables with a set of records to scratch. But when the contest arrives (Queen Latifah provides a lively cameo as the mistress of ceremonies), Q's hopes are compromised by his buddies' extracurricular activities. They plan to rob a grocery store and use Q's nightclub appearance as an alibi. The tubby, comical Steel and the earnest Raheem (who looks about 16 and already has a child) are not the instigators. The troublemaker is Bishop, for reasons that Mr. Dickerson (who wrote the screenplay) never successfully explains. Motivations are sketchy, as are the film's brief glimpses of its characters' home lives. But one thing that appears to push Bishop over the edge is watching James Cagney in "White Heat." Like many another budding gangster (the young English hoods in Peter Medak's "Let Him Have It" see "White Heat" too), he is enthralled by that film's vision of crime in terms of blazing, nihilistic glory. "That's the way to go, " Bishop says, when it's top-of-the-world time.