Copyright 1997 The New York Times Company The New York Times September 21, 1997, Sunday, Late Edition - Final SECTION: Section 7; Page 25; Column 1; Book Review Desk LENGTH: 228 words HEADLINE: Books in Brief: Fiction BYLINE: By Eric P. Nash BODY: SLIPPAGE Previously Uncollected, Precariously Poised Stories. By Harlan Ellison. Houghton Mifflin, $22. Harlan Ellison, the reigning bad boy of science fiction for more than 40 years, has mellowed - somewhat. Like Stephen King (who took more than a leaf from his stylebook), Ellison writes with a relish for gutter slang, veins-in-the-teeth violence and brand-name pop culture, and his work hums with a relentless narrative drive. Many of the stories in ''Slippage'' are light fables. Another, ''Crazy as a Soup Sandwich,'' about a modern-day demon, reads like a script for one of the more whimsical episodes of ''The Twilight Zone.'' (And it was, in the reprised series of the 1980's.) But the horripilating centerpiece novella, ''Mefisto in Onyx,'' which describes a black telepath's meeting with a white serial killer on death row, is a reminder that Ellison has not lost his capacity to convey stark, staring psychosis. He gets a little deeper into the killer's mind than is comfortable, emerging with ''the scent of the blossoming Yellow Lady's Slipper . . .. the odor that rises from a human body cut wide open, like a mouth making a big, dark yawn.'' This is the Ellison we know from earlier collections like ''I Have No Mouth and I Must Scream.'' Who else could end a story with ''The television licked its lips and winked at him''?