"Tender Mercies" is set in a small Texas town, embodied mostly by Waxahachie, a rural community outside Dallas that seems vaguely familiar from previous Hollywood incursions ("Bonnie and Clyde," for example) and evidently confronts residents with the bleakest terrain on the face of the planet.

In fact, "Tender Mercies," opening today at the Jenifer, seems to have been envisioned as a deceptively small-scaled opportunity for Robert Duvall to loom large in a starring role. He is Mac Sledge, a drunken, destitute wreck of a country and western musician who rehabilitates himself personally and professionally in the process of advancing from handyman to Man of the House on a little domicile on the prairie occupied by a devout war widow and her towheaded tyke.

A name like Mac Sludge would be more in keeping with the mood and tempo of the material, and the evidence on the screen reveals that it's Betty Buckley, in a now-you-see-her, now-you-don't, please-give-us-more-of-her-dear-God supporting role, who establishes the only persuasive claim on acting distinction.

Cast as the hero's notorious ex-wife Dixie, a vain and vindictive country and western star whose demands could conceivably drive stronger men than Mac to despair, Buckley keeps threatening to supply this incorrigibly sluggish, anticlimactic scenario with a reliable and electrifying energy source.

Obviously overpowered, the filmmakers persist in shutting her off in mid-surge by the infuriating, embarrassing ruse of cutting away.

For example, she enters singing, and the impact of her intense, eyes-closed country torching is so sensational that when Duvall walks out of the auditorium before her number is over and the camera follows him out, I felt a powerful urge to go up there and drag him back inside.

One of several attractive discoveries in "Carrie," where she played the sympathetic gym teacher, Buckley, who is now starring on Broadway in "Cats," seemed to blur into the TV suburban haze as the second spouse of the insufferable Dick Van Patten on "Eight Is Enough." All that time she was evidently cultivating a wallop that emerges with stunning but frustrating effect in "Tender Mercies," which isn't prepared to capitalize on her powerful, sexually incendiary presence.

You can understand why Duvall and screenwriter Horton Foote, who doubled as coproducers, might be irresistibly, though ungenerously, obliged to soft-pedal and short-circuit Buckley's performance, because Dixie stands out in a way that not only puts the leading player in the shade but also calls attention to the inherent weaknesses in the material.

I'm not sure what attracted a previously live-wire director like the Australian Bruce Beresford to such a deliberately repressed, backwater American project, but the star and writer are close friends whose professional collaboration goes back as far as the movie "To Kill a Mockingbird." Their pseudo-naturalistic pretensions are exposed as sheer lack of dynamism and storytelling acumen by Buckley's fleeting but ravishing appearances.

Buckley drives home the impression that the dramatically interesting part of Mac Sledge's life happened before "Tender Mercies" begins. We're obliged to observe an aftermath that never seems remotely as intriguing as that undepicted preamble. Moreover, it's an aftermath that remains grievously inadequate on its own terms, because Foote never gets around to authenticating the new, consoling marriage to the young widow, which is supposed to restore Mac's sense of self-esteem.

Although Duvall and Tess Harper, the newcomer stuck in the blah role of the nice young widow, Rosa Lee, are meant to fall in love and plight their troth after she takes him in, this absolutely essential relationship is left underillustrated to a point of self-defeating sketchiness.

"Tender Mercies" simply fails to take care of fundamental dramatic business. It's easy enough to see why Dixie might have laid waste to Mac but impossible to see why Rosa Lee would inspire him to do anything more interesting than repair the screen door or take out the garbage.

"Tender Mercies" fails because of an apparent dimness of perception that frequently overcomes dramatists: they don't always know when they've got ahold of the wrong end of the story they want to tell. TENDER MERCIES

Directed by Bruce Beresford; written by Horton Foote; director of photography, Russell Boyd; art director, Jeannine Oppewall; edited by William Anderson; associate producer, Mary-Ann Hobel; coproducers, Horton Foote and Robert Duvall. Produced by Philip S. Hobel for Antron Media Productions. This film runs 93 minutes and is rated PG. THE CAST Mac Sledge....Robert Duvall Rosa Lee....Tess Harper Dixie....Betty Buckley Harry....Wilford Brimley Sue Anne....Ellen Barkin