"Child Bride of Short Creek," the NBC movie at 9 tonight on Channel 4, fluctuates unsavorily between gloom and sensationalism. A very somber novelty, the fictitious film is based on a 1953 news story about an Arizona religious sect that practiced polygamy and, as depicted here, was such a tyrannical patriarchy that even Phyllis Schlafly might disapprove.

To add dramatic tension of sorts, writer Joyce Eliason devised a plot in which the spiritual leader of the group decides that his third wife is to be the virginal 15-year-old daughter of one of his followers. But the leader's son returns home from the Korean War newly aware of how stifling and corrupt this little world is, and he tries to rescue the girl.

Diane Lane, of "A Little Romance," plays the child bride -- she has perfected a haunting, intimidating look of betrayal for putting adults in their place, or melting hearts if need be -- and Christopher "Blue Lagoon" Atkins, almost unrecognizable with his clothes on, plays soldier boy. Atkins isn't an actor yet, but then, at least he isn't Richard Thomas, either. He's unassuming, and easy to take.

The young couple's romance could have been a tender clandestine affair, but TV's moral code, or the author's bad judgment, preclude even an implied consummation. Instead, life among the faithful is intercut with elaborate preparations by nearby state officials to raid the camp. When they do, the script requires Lane's character to make an abrupt and dramatically counterproductive about-face. The film keeps going off in one lunkheaded wrong direction or another.

As the leader, Conrad Bain contributes a certain seedy subtlety; he doesn't require much brimstone to come off as a deranged reactionary. Wisely, the filmmakers -- including director Robert Lewis -- show that there is danger and depravity beyond the camp as the old deacon has warned; when one girl escapes the camp, she is nearly raped by two lugs in a truck. And after Lane hears a forbidden rock song on the radio, she asks her mother, "What does it mean -- 'Take me in your arms and drive me out of my mind'?" Obviously, the outside world is screwed up, too -- just in different ways.