SOONER OR LATER in a thriller, the major characters find themselves stuck on a boat, a train, a plane, a spaceship, someplace they can't leave in a hurry. Someplace where the victim must face the killer in unfamiliar territory.

In "Narrow Margin," the scary venue of choice is a train, speeding through the wilds of Canada. The situation is this: Anne Archer has witnessed the brutal murder of an attorney at the hands of a mobster. When Deputy District Attorney Gene Hackman tries to get her to sing for the jury, he unwittingly leads the mob to her. Now both their lives are in danger, and the mobster (J. A. Preston) seems to have a much longer arm than the law. Through a series of circumstances, they find themselves on the aforementioned train, with at least two hired killers (James B. Sikking and Nigel Bennett) onboard.

"Margin," which was written, directed and shot by Peter Hyams, won't last an instant longer than its viewing. There isn't one special resonance left behind, not one truth revealed about people, not one moment of memorable suspense. But it's nevertheless fun to watch, fun to indulge in. It's a suspense potboiler. It manages to keep you going until the end and delivers the appropriate payoffs as a generic-brand thriller.

It's far better than it deserves to be, thanks to Hackman. Give this man a badge and you've got yourself a movie. As the unarmed agent who must outwit these strangers on the train, he puts in the Hackman ingredient.

"I like my side of the courtroom," he states with amiable cheekiness, when the mob makes him a sleazy cash offer. "The pay's not so good, but the air is much cleaner."

There are narrative holes and unanswered questions everywhere. You have to believe, for instance, that the two potential victims, continued on page 54 from page 52 knowing they're facing imminent death, are not prepared to leap off the train -- speeding or not. You wonder, where did this mysterious blonde woman come from? Just how many resources does this mob organization have anyway? When Hackman and Archer are speeding in a truck through thickly wooded mountains, while the bad guys follow overhead in a helicopter, why don't they just pull over and let the copter circle futilely around? But in this kind of movie, you make willing concessions because you want to be thrilled.

And Hyams does come up with decent thriller business: The killers know what Hackman looks like, but not Archer. The two have to keep apart. There are no phones on the train. There are a few surprises as to who's good and who isn't. And Hyams concludes the main action with a memorably campy flourish when Hackman informs the mystery blonde: "You know what I like about you? You're tall."

It turns out to be a devastating one-liner.

NARROW MARGIN (R) -- Area theaters.