You do come out of "Prince of the City" battered, shattered, shaken, stirred, drained, zonked and limp. You're a mess. But once the film's profound visceral effect wears off, there is time and good reason to wonder if it really has been all it aspires to be, or if it has aspired to be enough.

Sidney Lumet's extremely powerful, seemingly uncompromised film about moral compromise in the big dirty city, opening today at area theaters, is probably the year's Most Serious Movie so far; its seriousness alone is refreshing, and audiences weary of merry-go-rounds and escapist snacks may be delighted at having so much demanded of them (the running time is 2 hours, 47 minutes).

"Prince" could scarcely be more intense or persuasively bombastic than it is; if it were, patrons would be afraid to leave the popcorn stand and return to their seats. Yet the nagging impression remains that this story of how a big-city cop was trapped in the wheels of The System should be about more than it is and that if it were, it would be some sort of landmark dark epic in which the city is as much metaphor as setting.

The story -- written for the screen by Lumet and Jay Presson Allen -- is based on the experiences of New York detective Robert Leuci, who in 1971 was approached by the Knapp Commission to spy on and inform on his fellow narcotics officers. Danny Ciello, Leuci's counterpart in the film, thinks he has the power to pull his head out of the noose whenever he wants, but the noose gets tighter as the circle of interested and implicated parties gets wider and wider. It is almost a story worthy of Kafka.

Ciello is led mercilessly to his own Calvary; the vow he took in the beginning never to inform on his own partners, the single moral absolute to which he clings, must eventually be crushed in the battle of conflicting political expediencies around him.

Treat Williams, who played Burger in the movie "Hair," rose into a big boy in the role of Ciello. The slightly blubbery baby face is the very image of innocence, or innocence of a kind anyway. But Williams summons a battery of resources to give Ciello volatility and depth on the screen. By the end of the film, he and the audience are soul mates in exhaustion; one might be able to find false notes or overexertions in this performance, but nobody could say it wasn't absolutely relentless.

Lumet and Allen have somewhat affectedly divided the film into sections and given the sections too precious titles of their own. But the story does fall logically into three parts: the seduction of Ciello by the alleged reformers looking for corruption, later just scapegoats, in the city's prestigious special investigations unit, out to bust major narcotics suppliers; Ciello's perilous odyssey through the underworld, a mike and transmitter hidden under his clothes, crooks and cops becoming in some cases interchangeable figures in the same social tragedy; and the final, agonized attempt at expiation and absolution, when Ciello realizes he's in deeper, in several senses, than he ever knew.

There are key problems with all three movements. In the first, Ciello's motivation for risking the stigma of informer is not made clear enough, although an early and especially horrifying scene involving strung-out junky informers to whom Ciello supplies dope -- the movie's baptism by fire -- establishes the fact that controlling dope on the streets is a patently hopeless uphill fight. Informing on fellow cops may have been this young cop's only chance at heroics. Or so he may have thought; the movie doesn't quite say.

In the second section, it simply becomes too difficult to keep straight the large number of characters on both sides of the law or somewhere in between. And in the third, when Ciello himself is being vilified and accused, we have no way of knowing to what extent the charges against him are true, how corrupt Ciello himself has become, or whether his kind of corruption just isn't supposed to count.

The filmmakers do not want to be judgmental about him; that would make the picture fairly pointless. Yet, we've been following this character through hell, high water, fire and brimstone for more than two hours, and we deserve to be told straight out if there is any truth to the charges. We've invested a lot of emotional energy in Ciello, watching as the world shrinks about him, as he and his family become virtual fugitives themselves. Ciello's identity is leaked to a newspaper, and he must then be guarded around the clock, as protection both against the hoodlums and his fellows boys in blue, while the cases make their arduous ways through court.

Lindsay Crouse, as Ciello's wife, is not given much to do but stand around looking fearful, but she does this convincingly. Williams gets plenty of opportunity to bounce off the walls and the ceiling, and the scenes in which he's "wired" and in perpetual danger of exposure are stunningly suspenseful.

During one rendezvous with an enormous gangster named DeBennedeto (Ron Karabatsos), Ciello is found out, but he does a whirling dervish routine that Williams makes breathtaking; it is one of the film's true heartstoppers and brilliantly done.

But if Williams is a surprise, Jerry Ohrbach, who has stalked his way through such Broadway musicals as the current "42nd Street," is a revelation. He plays an older cop who, like Ciello, has found one noble value to place above all else -- loyalty -- but who, unlike Ciello, does not cave in and forsake it.

In the last third of the film, when Williams doesn't do much but suffer, Ohrbach gets to explode; he gets to read, and demonstrate, the riot act to one of the effete bureaucrats in charge of the investigation, and the audience is extremely grateful for one clear chance to cheer, one clearly defiant act of conscience.

Ohrbach is so good and so imposing, and he seems to epitomize so vigorously the tough realist with the dirty fingernails standing up to the posturing fops and twits, that many people may wish the movie had been all about him. It would have been so much easier that way.

But Lumet was scrupulous in avoiding simplistics, perhaps half regretting the syrupy excesses of his own "Serpico," a movie much less thoughtful than this one. As a director, Lumet is clinical and methodical, yet his films often burst with ferocity; he simply lets the actors handle the hystrionics instead of the camera, and this film has a large cast that amounts to a veritable convention of outstanding character actors. Virtually every characterization, down to the most minor, is meticulously and earthily detailed.

"The Onion Field" was probably a more deeply depressing lamentation about the futility of seeking justice within a system monstrously out of whack, but that picture didn't have the conceptual enormity of "Prince," which looks at the oft observed urban quagmire in a pretty disturbing new way. In the future, no retrospective of hard-edged films about crime and the city will be complete without it.

That doesn't mean the film is satisfying and accountable in all the ways it ought to be; Ciello's story seems to go to the very edge of something momentous and then not take that mercurial final step.

Rare is the movie, of course, that is All It Could Be, but the frustrating ones are the ones that get that close, not the ones that never have a prayer. When you finally make your way out of "Prince of the City" -- the ushers release you on your own recognizance -- when you pull back from the fireworks and the pyrotechnics, the big picture is just a little too small.