L.A. Confidential.

YOU must have noticed that in thrillers there is usually something that doesn't quite make sense. There was no reason for Amanda to wear a hat to the corner grocery, for the Brownstein twins to have missed school because of their mother's migraine, for there being an expert on Byzantine art on the bus that day. But that is how thrillers are -- mostly.

I am happy to report that in L.A. Confidential there is nothing of the kind: everything is credible, fits in with all the rest, and goes from exciting to enthralling. The plot is absorbing, the characters are believable and even worth caring about, and the dialogue is tough and witty without ever sounding strained. This is as close to art as a policier can get, and that should be plenty for everyone. James Ellroy's underlying novel is, I gather, more complicated; all the more credit to the writers, Brian Helgeland (whose Conspiracy Theory failed to impress) and Curtis Hanson (who also directed), for getting at the essentials, and getting them right.

We are in the City of (Fallen) Angels in the Fifties, the Eisenhower and Norman Rockwell decade. Here, at least in the movies, it is always midsummer a-rustle with palm fronds, although they are only a front behind which prostitution, pornography, drugs, and murder pullulate. Mickey Cohen, the crime czar, is safely behind bars, but the vacancy at the top merely invites rubouts as various contenders compete for the throne of crime. As the L.A. police employ ruthless tactics to rid the city of criminal elements, one wonders just how clean their own hands are.

Mainly, this is the story of three very different detectives. Bud White is thorough but unscrupulous in meting out punishment, even instant death, in what he perceives as the righting of wrong. He is particularly violent with abusers of women, harking back to his father's vile treatment of his mother. And an effective one, though unwilling to testify against other cops, however culpable.

Bud's exact opposite is Ed Exley, a cerebral, bespectacled type ("You better lose those glasses," his superiors keep telling him, and sometimes he does), who, however, yearns for action. Above all, he hopes to match his late father's fine career in the Department, and perhaps even root out the old man's still unknown killer. Ed believes in ideal justice, which makes him and Bud natural enemies, especially after Ed testifies against some bad cops and ends up shunned by his colleagues.

The third, and most curious, principal is Jack Vincennes, a dapper, morally lax detective who not only acts as paid advisor on a dubious TV police show, but also teams up with Sid Hudgens, the sleazy editor of Hush-Hush magazine, which specializes in setting up movie celebrities in compromising situations. This involves much greasing of palms, fake publicity for Jack, who makes the well-photographed arrest, and good gossip for Sid. Jack, though, is very smart and, as it turns out, not such a bad guy.

Los Angeles needs all the police work it can get. Quickly, the movie establishes a sense of spreading evil, especially as we keep hearing about the Fleur de Lys, where all desires will be fulfilled. It turns out to be a place (which the film does not show in detail) where you can have sex with girls who have been made over into movie-star lookalikes; indeed, in a delightful throwaway scene, Ed mistakes -- much to Jack's amusement -- the real Lana Turner for such a knock-off. But isn't that the essence of Hollywood? Where even the real is make- believe, may not the make-believe be as good as real? Or as bad as real? It is Christmas Eve, yet a husband is beating the daylights out of his wife under the colored lights, and the cops at the station house are brutally working over some Mexicans who may not even be guilty. The former is punished by Bud; the latter, despite Ed's efforts, are not stopped.

It is to the movie's credit that it works mostly by suggestion. So Lynn Bracken, the blonde from Idaho who is the Veronica Lake of the Fleur de Lys, is amply characterized with utmost restraint. So, too, a corrupt D.A. and whoremongering politician are sketched in authoritatively with swift, subtle strokes. All locations are redolent of lived-in authenticity (and don't go telling me that Hollywood necessarily knows how to get L.A. down right). We believe a weatherbeaten type such as Police Captain Dudley Smith, more pragmatic than ethical, to be good at his job; or Pierce Patchett, the millionaire who makes as much from highway construction as from the byways of the Fleur de Lys, to be terrific at bending the law his way.

Everything has a fresh feel to it: Lynn's similar yet different effects on Bud and Ed; the uneasy alliances, first between Ed and Jack, then between Ed and Bud; the seamy operations of the forces of law in all their meanderings; the suddenness with which unconscionable violence strikes; the horrendous shootouts that register as more real than standard movie shootouts. The dead here look genuinely dead; more important, the living are genuinely alive in their imperfect, begrimed, vulnerable existences.

And how cleverly the film is cast. Two of the leading roles have gone to Australians or New Zealanders, sufficiently unfamiliar looking, yet blending in seamlessly. Thus the babyfaced bully, Bud White, of Russell Crowe and the slightly nerdy yet brilliant Ed Exley of Guy Pearce. And how neat to cast James Cromwell, formerly Farmer Hogett of Babe, as the pawky Captain Smith. The until recently too gorgeous Kim Basinger, now beginning to fade, is just right for the disenchanted Lynn. Possibly the finest character actor in today's Hollywood, Kevin Spacey gets across with wonderful irony both the self-satisfaction and the self-loathing of Jack Vincennes. Perfect, too, are the slippery D.A. of Ron Rifkin and the exquisitely unsavory nabob of David Strathairn. Also the cheerfully slimy Hudgens of Danny DeVito, and the pathetic young actor for homosexual sale of Simon Baker Denny.

Dante Spinotti's cinematography, pretty but not too pretty, captures expertly this two-faced world, and Jerry Goldsmith, not always my favorite composer, admirably blends lushness and menace in his score. But top credit must go to Curtis Hanson for his astounding film-noir savoir faire: scene after tricky scene is directed with quietly devastating command. L.A. Confidential conveys supremely how brains and brawn must unite to achieve, however transiently and with some compromise, the triumph of justice. It is sure to become a classic of its genre.