If Peter Hyams had scaled back his ambitions any further in the thriller "Narrow Margin," there'd be nothing left but a line drawing.

The picture, which stars Gene Hackman and Anne Archer, has been cut back to bare bones -- no subplots, no romantic diversions, a small, functional cast -- and initially, this purity of focus is tantalizing. In Los Angeles, Carol (Archer), a recent divorcee, agrees to go out on a blind date with a man she knows almost nothing about, except that he's a friend of a friend and a hotshot lawyer from New York. The man's name is Tarlow (J.T. Walsh), and during dinner at his hotel he's called to the phone and asks his date if she would like to wait in his room while he finishes up his business. Shortly thereafter -- while she's powdering her nose -- Tarlow has visitors, a mob boss named Watts (Harris Yulin), from whom he has been stealing money, and a friend. The friend has a gun. Something bad happens. Something that Carol sees.

For Los Angeles Deputy District Attorney Caulfield (Gene Hackman), Watts is the Big One. He wants him bad, and so when news reaches his office that Carol was an eyewitness to the incident, he heads up into the Canadian mountains, where she is hiding out, to bring her back to testify. Unfortunately, by the time it's discovered that Watts's men have followed Caulfield and his partner, Sgt. Benti (M. Emmet Walsh, who plays the character as a kind of hick Saint Bernard), to Carol's hideaway, and the gunfire and chases begin, we become weary from the lack of invention, formula-weary.

Once Caulfield and Carol make it onto a train to Vancouver -- the only avenue of escape from their would-be killers -- a game of lethal cat-and-mouse ensues and the action intensifies. There are some satisfying moments during this long middle section, all of them from Hackman. Nobody is more extraordinary at playing ordinary men than Hackman; he has a genius for the commonplace. Here, he's playing the most ordinary character of all, a simple, decent man. Caulfield is almost completely without complexity; he does what he does because he likes to put bad guys away. Yet Hackman makes Caulfield seem heroically prosaic. He's the sort of actor who makes us hang on every detail, no matter how inconsequential. This is a tour de force performance without looking like one.

Without Hackman, "Narrow Margin" would be nothing; even with him, it's pretty much nothing. Archer gives a serviceable performance, but the role is too thin for her to make anything out of it. Hyams keeps the action percolating, but he can't personalize it. Most likely Hyams -- who also wrote the script -- felt that he was working in the spirit of hommage by staging classic movie situations like the one in which the characters chase each other across the top of a moving train. And by confining the film's action mostly to the train itself, he may have thought he was alluding to a film like Hitchcock's "The Lady Vanishes." But "Narrow Margin" feels more tired than classic, even if it manages to provide some thrills. There's just not enough there to grab us.

Narrow Margin, at area theaters, is rated R and contains some scenes of violence.