March 27, 1992 |  In sharp, striking  contrast to the flash and filigree of Oliver Stone's stylistically brilliant JFK, John Mackenzie's Ruby, the latest bit of Warren Commission-bashing, has the low-rent look and blunt-edged directness of no-nonsense B-movies from the 1950s.

If nothing else, the new film is an apt marriage of style and substance: The tawdriness of its storytelling technique is altogether appropriate for its account of a seedy bit player who somehow managed to gate-crash into history.

It is the provocative conceit of screenwriter Stephen Davis that Jack Ruby (Danny Aiello), the man who fatally shot accused presidential assassin Lee Harvey Oswald, was an extremely small cog in a tangled machine of Mafia big wheels fueled by CIA spooks. The movie follows Ruby for a year or so before his infamous crime, viewing him sympathetically, if not approvingly, as an insecure outsider, a Jewish hood from Chicago who's pathetically eager to please his Sicilian Mafia overlords while running a two-bit striptease club in Dallas.

Ruby isn't an entirely loyal soldier -- he does some part-time snitch work as an FBI informant -- but he's always reliable. He drops everything when he's ordered to Cuba, where a powerful mobster is languishing in a Havana prison. Ruby figures he's supposed to use his drug-running contacts to smuggle the mobster back into the United States. It's the first of several serious mistakes he makes while staggering through a labyrinth of deceptions and conspiracies that leads to the underground parking garage of Dallas Police headquarters.

Ruby claims -- or, to be more precise, suggests -- that Mafia dons and CIA operatives joined forces to defeat a common enemy. At first, it appears their target is Fidel Castro. But then the plan changes, and Ruby discovers -- much too late for him to do anything about it -- that the hit men have an entirely different target in mind.

Director Mackenzie (The Long Good Friday) is deliberately vague about the details and extent of the assassination conspiracy, and gives the audience only as much information as Ruby himself can uncover. And Ruby, for all his naiveté, understands all too well that he knows just enough to make himself seem foolish, or worse. ''That's how they operate,'' Ruby explains in a moment of painful lucidity. ''They know if you talk, you'll sound like you're crazy.''

Worse, you might sound like one of those conspiracy nuts.

The paranoia level is ratcheted up a few more notches in the movie's best scene, a late-night encounter between Ruby and a CIA operative played with darkly bemused menace by Arliss Howard. Their conversation underscores the screenplay's theatrical origins -- Davis adapted the script from his own stage play, Love Field  -- but the cryptic wordplay nonetheless is mesmerizing and unsettling, even as it is laugh-out-loud funny.

The rest of Ruby is interesting, and occasionally exciting, without being exceptionally gripping. Most of its emotional appeal stems not from the intricate plotting, or even the volatile subject matter, but rather from the power of Danny Aiello's surprisingly affecting portrayal of Ruby as a well-meaning worm who turns too late.

Sherilyn Fenn, late of TV's Twin Peaks, is fine as a character invented by the moviemakers: Candy Cane, an ingenuous stripper who shares a platonic friendship with Ruby -- she brings out the paternal instinct in him, just as Fenn brings out a soft side of Aiello -- and has a fateful Las Vegas tryst with another historical figure. The character is more of a plot device than anything else, a touch of pulp-fiction romanticism. Still, Fenn gives her poignant undercurrents of yearning and vulnerability.

Ruby vividly evokes a '60s ambiance with a minimum of self-conscious fuss, and makes the most of what appears to have been a limited budget. Rude and crude, this is tabloid movie-making of a sort that, like good junk food, can be enjoyed even while you remain dubious about its contents.