IS ANYONE GOING to buy Martin Sheen as a mean leatherneck -- especially if he doesn't?

In "Cadence," which also marks his directorial debut, he's a bigoted, prisoner-chewin' stockade sergeant who keeps his black inmates scared spotless.

At least, that's the idea. But Sheen has "nice guy" etched all over his not-ready-for-double-time face. He can't hide the intrinsic geniality in his eyes. His voice dips with embarrassment when he barks out racist slurs. When he "struts menacingly" around the camp (picture a savage, gray-haired kitty in fatigues), the military rat-a-tat-tat drumming on the soundtrack becomes unintentional mockery.

Moviegoers, this film seems to be saying, please ignore the wimp behind the curtain.

While you're at it, you might want to ignore the story in front of the curtain. Grieving over the death of his father, Pvt. Charlie Sheen (one of three Sheens in this film, including Ramon Estevez) gets 90 days in the stockade for beating on an MP. Slouching into camp with an eight-ball tattoo on each hand and a serious bratitude problem, he soon makes an enemy of real-Dad Martin when he refuses to call him Sarge. As the only white prisoner, he also has to contend with tough inmates Larry Fishburne, Michael Beach, John Toles-Bey, Blu Mankuma and Harry Stewart.

The predictable rites of jailbird passage take place, as Charlie takes a beating but doesn't rat, plays basketball with the guys and slowly picks up their synchronized song-and-march routine. When Charlie decides to repair a windmill (in memory of days with his dead dad), Martin thwarts him at every turn. But Charlie persists until the repairs are completed.

The growing Sheen-to-Sheen enmity -- ostensibly the main conflict in the movie -- leads to a drunken fisticuffs challenge, spitefully ordered emergency drills, a fatal gunshot and a court-martial. It also involves a potential rift between Charlie and the black inmates. But emotions in this film operate on a made-for-TV level; they don't engage you.

If there is a high point in the movie, it's that choreographed "Soul Patrol" number, as the inmates perform duties and riff colorfully on Sam Cooke's "Working on the Chain Gang." That's a minor cadence to remember a whole movie for.