"The Long Riders" appears to be a perfectly realized movie. An intelligent, unsentamental distillation of the decline and dissolution of the James-Younger gang, it boasts beautifully modulated direction by Walter Hill, effective performances, and evocative period flavor in both externals and essentials, notably the depiction of the James Brothers, the Younger Brotherss and their outlaw associates as an integral, albeit criminal, part of the rural American society of a particular time and place.

In short, "The Long Riders" seems a flawlessly felt and visualized western, true to the subject matter and the aspirations the filmmakers probably held for it.

The catch is that I suspect that only moviegoers with a deep regard for western lore and classic western moviemaking will be drawn to the film's graceful, revealing authenticity and then strongly impressed by it.

Hill has certainly brought pictorial class to this project without obscuring or romanticizing the characters. For all one knows, "The Long Riders" is destined to take its place among the most respected examples of the genre. What it doesn't seem to do is transcend the genre. Will it appeal to people who usually ignore westerns? Highly unlikely. And if it doesn't, westerns will continue in their current state of eclipse. Last year's "Butch & Sundance: The Early Days"was also beautifully shot, but it never began to attract a public.

"The Long Riders" has an intriguing casting gimmick: actor siblings portray the outlaw siblings. The Caradines -- David, Keith and Robert -- impersonate Cole, Jim and Wes Younger, respectively. Stacy Keach plays Frank James to brother James' Jesse. Randy and Dennis Quaid do Clell and Ed Miller, respectively. Christopher and Nicholas Guest are the Fords, Charlie and Bob, respectively.

Everyone performs crisply and leaves a distinctive impression. Indeed, expert acting seems to be the norm. The Guests play the Fords as if they were ludicrous knickknacks, a funny set of something-or-other. Their scraggly whiskers and slicked-down haircuts are identical, and they move in unison. Randy Quaid endows Clell with an amusing, eminently believable deadpan complacence when confiding how all the boys hit the outlaw trail. "We robbed a Yankee bank, 'cause it seemed like a good idea at the time . . . We just got in the habit. I guess we'll keep on a-goin' till they lock us up . . . or hang us."

James Whitmore Jr. is excellent as a Pinkerton agent, characterized without condescension or partisanship as a concientous professional guilty of inexperience and misjudgment in his early attempts to apprehend or intimidate the gang. Pamela Reed, her husky, insinuating voice a cynical challenge and her knowing, spunky expression a troublemaking erotic invitation, is so good as Belle Starr that it seems a pity she never evolves into a major character.

There's something explosive in the air when Reed's Belle needs to get her kicks. Provoking a knife fight between Cole Younger and her halfbreed husband, Sam Starr, Belle reminds them, "Boys, there's no need to fight over little ole me . . . but if you've got to, you make it man-to-man and hand-to-hand." Bad medicine, this girl.

The story begins in the early 1870s with the depiction of bank robbery that ends tragically when Ed Miller panics and begans shooting helpless customers. There's no attempt to gloss over the activities of these desperadoes. They're identified as unreconstructed thugs and cutthroats who nevertheless have their reasons, their normal family and social connections and a peculiar sort of standing in the community. The contradictions feel absolutely right: You're convinced that the boys moved in and out of law-abiding society in this nonchalant fashion, that the attitudes and traits ascribed to them are essentially accurate.

The climactic episode is the disastrous bank robbery attempt in Northfield, Minn., in 1876. Alerted to the gang's approach, the townspeople armed themselves and shot back with withering effectiveness when the shooting began. Hill's staging is far more elaborate but also more powerful than the same confrontation in Philip Minnesota Raid," an unconventional treatment of the James-Younger legends made in the early '70s. u

Hill's agonizingly detailed, slow-motion shootout is the best sequence of its kind since Peckinpah hung up his weapons. The exchange of fire goes on and on, and each shot that hits is given a peculiar, shattering individuality. Hill is a director who knows what efects he wants and rarely wastes esthetics ammunition. At the same time, he has a tendency to practice on somewhat overspecialized targets.