Sergio Leone's "Once Upon a Time in America" has the mind of a dazzling art film and the soul of a TV mini-series. The movie isn't boring, exactly, although it is long -- presented here in Leone's original cut, these four hours (with intermission) float with his craftsman's confidence, the sureness of his construction, the majesty of his master shots. By the end, the gap between Leone's cinematic genius and the humdrum familiarity of his story induces a kind of hysteria; his movie is that most irritating of anomalies, the lavishly photographed potboiler.

"Once Upon a Time in America" tells the story of five friends, all Jewish, who emerge from New York's Lower East Side to become gangland heroes during Prohibition. David Aaronson (Robert De Niro), nicknamed "Noodles," is a romantic, and sort of lazy (he just wants enough money to hang around the beach). His chum Max (James Woods), an ambitious pragmatist, masterminds the gang's rise.

Needless to say, dames get in the way. Noodles pursues Deborah (Elizabeth McGovern), destined for stardom on the stage; Max falls in with the demimondaine Carol (Tuesday Weld). They kill. They open a speak-easy named Fat Moe's. They protect a union leader, Jimmy O'Donnell (a typically self-infatuated Treat Williams), and union corruption is born.

In the studio's shortened version (which opened here last year), the plot proceeded chronologically. Here, the action moves seamlessly in and out of time, from the gang's childhood on the streets to Prohibition to middle age and back again. In one scene, memories are linked by a ringing telephone in the rememberer's present; in another, the taillights of a '60s garbage truck become the headlights of a '20s automobile. But this artistry is lavished on the most hackneyed of narrative structures -- Noodles has returned to the old neighborhood to unravel his past. And when said past is unraveled, it turns out to be the kind of pseudo-"Dorian Gray" nonsense you'd expect from something like "Lace."

Leone and his cadre of screen writers (six, including Leone, are credited) never really decide what we're supposed to make of these gangsters. They're careful with the details of period setting, careless with social context -- the long segment about the gang's childhood (featuring a particularly inept crew of young actors) never tries to explain why these kids turn to crime. And the actual mechanics of organized crime, sketched so gracefully by Francis Coppola in "The Godfather," aren't even addressed in "Once Upon a Time in America." In this movie, the streets really are paved with gold; before you know it, the gang has stumbled into power and fortune.

Leone is entranced by the mythology of the gangster, but he's also suspicious of it. He wants to show us what gangsters were really like, but he does it by taking a shortcut -- instead of working to build a milieu, he pumps up his movie with doses of supercharged violence. In its beatings and gunfights, "Once Upon a Time in America" features the kind of visceral wows the screen hasn't seen since the heyday of Sam Peckinpah. Noodles brutally rapes both Deborah and Carol; the point of these scenes is to lend ambiguity to the gangster romance, but this edge of realism doesn't come out of anything. Leone's just using one myth to color another.

De Niro may be at the stage in his career where he can't give a bad performance. In middle age, Noodles' walk is a broken jumble, and his face sets into a kind of bemused stoicism that seems identifiably Jewish. But it's been years since De Niro has had a role he could sink his teeth into, and Noodles is no exception. The movie's four hours long, but no one had the time to write a single real character.

Woods is menacing in his usual scarface way, but his Max is a mastermind without a thought in his head -- all sorts of savvy is ascribed to him, but you never see his wheels spinning. And McGovern's face has widened to the point where she's preposterous in the ingenue roles she keeps getting. She has the big potato-face of Charles Kuralt, and the only acting she does consists of the kind of amateurish Method shrieking that makes you wish Lee Strasberg were around to shout, "No, no, that wasn't the idea!"

There is some fine acting around the edges, though. Nobody's better at trashiness than Weld; her cheekbones and big, deliquescent eyes hang from her face like fruit too long on the vine -- you can smell the rot of her. William Forsythe is scarily sleepy as Cockeye, one of the gang -- this smooth-faced kid would kill you as soon as he'd pick his teeth with a match. And that reliable sloven, Burt Young, brings the movie the kind of realistic texture it could use more of.

But Leone has no feel for realism. His spaghetti westerns worked because of the spaghetti -- set in a mythic time and place (which was actually Italy), they were exercises of pure style, founded on archetypes and spare, linear plots. The avant-garde just won't play in the shadow of the Williamsburg Bridge, amid cobblestones and garbage cans. He's a metaphysical filmmaker; caught in alleyways that never see the horizon, he's spectacularly cramped.

Once Upon a Time in America, opening today at the Key, is rated R and contains graphic violence, sexual situations and profanity.