B MOVIES, like fortune tellers, thrive on unlikely prophecies and cheap effects. "Night of the Comet" is grade-B parody, a revisionist "Day of the Triffids," a cosmic "Night of the Living Dead."

Catherine Mary Stewart and Kelli Maroney costar as a couple of gutsy Valley girls who survive a close encounter with a giant comet. It's a non-atomic apocalypse, in which all but a few creatures turn into red dust. Sisters Gina and Sam Belmont find their mom's dress out by the barbecue with her lover's shoe. "Here's Chuck," says Gina, pouring what looks like paprika out of an outsized white buck.

Those slightly exposed to comet rays turn into ravenous zombies, one of whom eats Gina's boyfriend Larry. Luckily, the sisters were combat-readied by their soldier dad. Besides, as Gina says, "The mach-10 machine gun was practically designed for housewives."

The sisters hook up with a handsome truck driver who may be the last man on earth. Robert Beltran, the main course in "Eating Raoul," plays the Latino hero Hector. The three take on the zombies and a group of survivalists who want survivors' blood to fight off the dread comet-osis.

Cult star Mary Woronov, whom Playboy dubbed "Queen of the B's," is one of the survivalists. It was also she who ate Raoul. But this time, Beltran finds a more satisfying fate in the arms of Stewart, who gets the last man as handily as she did "The Last Starfighter." She and Maroney are the strongest heroines since Sigourney Weaver in "Alien," pragmatic, tough little pugs, with sure futures in action comedy.

The effects, smog shot through a red lens and piles of clothes on the streets, look like a "Night at the Red Chinese Laundry" instead of the day after a heavenly disturbance. And the plot is frequently derailed to present various ghouls in various states of decomposition. It was written by director Thom Eberhardt after a lunch with three 12-year-old actors. Eberhardt's hand isn't sure and "Night of the Comet" wobbles in its orbit. NIGHT OF THE COMET -- At area theaters.