By Ty Burr
Updated December 03, 1993 at 05:00 AM EST

In director Stephen Gyllenhaal’s movies, small-town tragedy builds by accretion. His Paris Trout adapts Pete Dexter’s novel about a southern crank (Dennis Hopper) whose racism erupts with hideous consequences. Waterland is a melancholy stunner in which schoolteacher Jeremy Irons can’t break free of boyhood ghosts. Killing in a Small Town follows a Texas mom (Barbara Hershey) who one day just picks up an ax. His latest film, A Dangerous Woman (R), stays the course. Like the others, it’s based on a well-regarded book (by Mary McGarry Morris); like them, the story hinges on a loner who’s one step out of synch and whose actions are fueled by the petty torments of others. This time, though, Gyllenhaal’s gift for making the mundane mythic fails him.

Debra Winger plays Martha Horgan, a graceless near-simpleton for whom a supermarket clerk’s asking ”Paper or plastic?” represents existential dilemma. Martha lives with her youngish aunt Frances (Hershey), a widow stuck in an affair with a married local politician. The arrival of a strapping itinerant handyman named Mackey (Gabriel Byrne) sets up a classic fox-in-the-henhouse triangle. Meanwhile, Martha’s friendship with a coworker (Chloe Webb) is shattered by the woman’s duplicitous boyfriend (David Strathairn, in a rare sleazeball role), who has a knack for pushing Martha into messy, defensive flusters.

As usual, Winger’s good enough to hoist her role above the expected ugly-duckling Oscar bid. You understand why Martha makes people nervous, and why they make her nervous; you see her self-consciousness gain an edge of hostility as the movie progresses. Yet there’s a precious vagueness in the script by Naomi Foner (Running on Empty) that keeps the characters at arm’s length. In Morris’ novel, Martha’s oddness is partially explained by a traumatic gang rape in her past; here, she’s untethered by previous events.

Hershey, too, is stuck in a part that’s annoyingly undefined. Even though we learn concrete facts about Frances, we rarely get a sense of who she is. When the actress’ talent surfaces in a raw late-night drunk scene, the specificity of character comes as a shock. (Part of the problem may be that Frances narrates the movie, and narrators tend to be unexamined stand-ins for authors themselves.)

By contrast, Byrne brings his meaty Black Irish authority to the role of Mackey, a screwup who’s no better off for knowing he’s a screwup. Mackey’s sensitive, he’s smart, he drinks too much — in other words, he’s a walking cliché — but Byrne finds the man’s heart. And Gyllenhaal finds surprising eroticism in Mackey’s seduction of Martha, a queasily touching scene in which explicitness for once feels earned.

Their relationship is so intriguing that it’s a letdown when the movie turns first melodramatic, then preposterously upbeat in the homestretch. It’s one thing to imagine Martha capable of murder, and even of the saintly serenity with which she faces justice: If Gyllenhaal and Foner want to paint her as a backwoods Prince Myshkin, Winger has the stuff to pull it off. But Dangerous Woman’s final scene ignores the real bitterness that has led up to it. Much is made of Martha’s naive inability to tell anything but the truth (thus, the title). In a sense, though, she doesn’t have to lie. The movie ends up doing it for her.