CBS throws another log on television's vigilante fire with its Sunday night movie "Rockabye," a pandering potboiler at 9 on Channel 9. Print ads for the film show the star, Valerie Bertinelli, brandishing a handgun while the nearby caption advises, "She was young, trusting and naive. Until someone stole her son. Then she was deadly."

Actually she was young, trusting, naive and infernally stupid -- they forgot that last part -- and remains so throughout the film, but she doesn't actually get her deadly little paws on a handgun until the last 20 minutes or so. CBS is hoping that will be enough gun-toting to appease the blood lust of the audience.

Viewers hoping for shoot-outs will have to be patient, forgiving and probably as pudding-headed as the heroine, because the script by Laird Koenig, from his "novel" yet, is a preposterous concoction without a shred of verisimilitude. Koenig and Bertinelli deserve a backward kind of credit because they manage to make the character of a cute young woman whose child has been abducted not only unsympathetic but downright aggravating.

In the opening scenes, Susannah Bartok (Bertinelli), no relation apparently to Bela, finding herself stranded overnight in New York because she missed a bus to Vermont, takes her 2-year-old son Sonny on a stroll along 42nd Street -- probably not the wisest course of action for anyone wishing to see another sunrise -- and heedlessly checks in at an unmistakably unsavory hotel. Before she knows it, she has been maced in front of Macy's (a cute touch) and the son kidnaped.

Those mean old New York police don't believe her story, preoccupied as they are with jelly doughnuts; cop impotence is a part of the vigilante fantasy formula. But a tough and feisty Cuban-born reporter, played with brash authority by Rachel Ticotin, takes Bartok under her wing in hopes of getting a splashy story for her tabloid. And sure enough, the tabloid runs a headline that would certainly stop every single one of those jaded New Yorkers in their tracks:

"Young Boy Kidnapped."

"Young Boy Kidnapped"??? Oh, my God! To what tawdry depths will these yellow journalists sink next?

Soon the scenario boasts more red herrings than a Moscow fish market. An effeminate psychic is brought into the picture, and a mean old, and cheap old, newspaper editor complicates things pointlessly; and finally, halfway through, the anguished mother stumbles across a black-market baby ring that, as it turns out, has an inventory of precisely one baby. That leads to an unlikely showdown in an unlikely location, a rat-pocked hovel, and then on to JFK Airport for a ludicrous climax.

Through it all, our button-nosed heroine seems hopelessly dumb, and when she isn't dumb, she's thoughtlessly ungrateful to the reporter who risks, and even gives, her life in the pursuit of this case. But the message of the picture, which has been competently directed by Richard Michaels, is that it matters not that you're stupid once you get a gun in your hand.

Bertinelli seems about as authentically maternal as Edward G. Robinson, but the film is, in a way, her baby, since it was coproduced by Bertinelli Productions. That's how networks such as CBS reward stars of hit series like "One Day at a Time"; they buy lousy movies from companies the stars set up to search out projects that will make them look good. This time, everybody goofed. And nobody looks good.