CBS, understandably enough, is not referring to "Out of the Darkness," its Saturday night movie, as a "docudrama." The term became poison last year during the uproar that followed the recklessly contentious CBS mini-series "The Atlanta Child Murders." In August, CBS announced it was dropping plans to produce "Saigon," a docudrama mini-series about the Vietnam war. The network didn't want to go through the same ruckus again.

"Out of the Darkness," at 9 tonight on Channel 9, certainly is based on fact, and, like the Atlanta mini-series, grisly fact: the reign of terror wreaked by David Berkowitz, the "Son of Sam" killer, in New York eight years ago. Fortunately the purpose of the film is not to take a contrary position to the verdict in the case, nor to give us a play-by-play reenactment of a murder spree. It concentrates on a small but engrossing corner of a city's pulpy tragedy.

"Darkness" is the story of one of the policemen involved in the search for the killer and how events in his private life affected his work -- how his confrontation with the killer and the specter of death helped reconcile the loss of someone he deeply loved. The story, however true, is hauntingly told by writer T.S. Cook and director Jud Taylor. They keep two parallel lines -- the investigation and the cop's domestic strife -- going through the film and almost bring off the trick of having them meet at the end.

Martin Sheen plays Ed Zigo, the Brooklyn detective who, with his partner, went to Yonkers one day in 1977 to check out a hunch involving a parking ticket. This led to the capture of Berkowitz and the end of his murderous binge. Jennifer Salt is plausibly near-saintly as Zigo's wife, who becomes unexpectedly ill and must enter the hospital for a heart valve replacement while the search for the killer is going on.

Sheen convincingly conveys the anguish and then the resilience of Zigo. The portrait is flattering -- he's referred to as "the best homicide guy in Brooklyn" -- perhaps in part because the real Zigo served as technical adviser to the film. Still, the emotional and dramatic points made are valid, the account of no-nonsense cop work unhurriedly creditable, and the ambiance of dread that overtakes a city when a mass murderer is at large evoked with gritty veracity.

Other key performers include Hector Elizondo as a priest who is a friend of Zigo's and runs an aquarium (he elicits a pretty good Cagney impression from Sheen in one scene) and Eddie Egan, the former cop whose tale was told in "The French Connection," as the head of the "Son of Sam" task force. Egan's real-life police partner, Sonny Grosso, is coproducer of the film.

The killer performance, in at least two senses of the word, is Robert Trebor's as Berkowitz. He doesn't even appear until the last quarter, but he makes an unnerving chilled-to-the-bone impression. With his eerily winsome grin and playful manner, even after being caught, he is the picture of pathetic cunning. On the way to be booked for murder, he tells Zigo, "I hate to look like this on TV. Could you comb my hair a little?" Zigo obliges.

Not everything that happens in the film relates directly to the murder investigation or to Zigo's troubled home life. There is some spurious mayhem involving a man who takes first his own child, then a woman on the subway, hostage (the subway scene and the involvement of Egan and Grosso stir irrelevant "French Connection" connections). Apparently these scenes are to convince us that Zigo is a model cop. Yet, encouragingly enough, he is shown as fallible, too, particularly after enduring his own life-size trauma.

Sheen's son Charles has a brief cameo; he's a man with shaving cream on his face who slams his apartment door in a cop's face when asked for information about the murders. Like many other of the film's details of life in New York, this one rings bitterly true.