OCTOBER BLOOD. By Francine du Plessix Gray. Simon and Schuster. 253 pp. $16.95.

THERE IS probably a compelling novel to be written about the under hem of the fashion world and a ruthless fashion magazine, but October Blood by Francine du Plessix Gray isn't it. Gray, the author of Lovers and Tyrants and World Without End would seem to have the right credentials for the job -- she's the daughter of a former hat designer known to her smart set clientele as Tatiana of Saks, the stepdaughter of Alexander Liberman, the editorial director of Cond,e Nast, publishers of Vogue, and was reared in France, the home of haute couture. There's no question that the author knows her territory -- designers Jacques Fath, Jean Desses, Coco Chanel, Balenciaga, Dior -- all make brief appearances; unfortunately name-dropping is no way to give authenticity to a novel otherwise so bereft of it.

October Blood centers on three generations of Fitzsimmons women, all of whom devoutly believe that rebellion is the only way to sanity. Nada Fitzsimmons is the editor of Best, "the most influential fashion magazine in America, perhaps in the world." When she is not holding court at the Paris collections, she is busy making declarations that "were as widely quoted at Dale Carnegie's or Monsignor Sheen's: Beauty is the only promise of happiness we have," or perhaps, "The most primitive tribes understand the spirituality of costume" or, "All that is profound needs a mask."

Her daughter Paula, the novel's sometimes narrator (like Lovers and Tyrants, October Blood alternates unaccountably between first and third person) struggles mightily to find her place in a world where artifice is everything. Dabbling in theater and mysticismand madness, beginning what will be a lifelong affair with Nicholas Hollins, the little-boy-lost son of Nada's best friend and Best colleague, marrying Julian, an ex-priest turned journalist who viewed her as "a dandelion wafted by wind . . . the rare flower burning blue on icy mountains that men climb dozens of miles to find" and giving birth to a high-spirited daughter are chief among Paula's attempts to establish herself.

Gray is successful at showing that the concerns of the fashion world are as lightweight as a Chanel chemise: "I listened to them all making the familiar din. . . . 'Is it true about the Aga Khan?' 'Yes, yes, absolutely, he's left his redhead contessa and taken up with a Swedish cabaret girl, the Begum is livid.' 'How was Gstaad this winter . . . ?' 'Don't even mention that word, only place to be seen this year is Courchevel . . .' 'Nada, darling, is it really true about Saint-Laurent simply sweeping Paris yeaterday?' "

ACTUALLY, Gray is too successful. Just as it is difficult to write about bores without being a bore about it, so is it difficult to write about shallow people without sounding as foolish as they do, and the endlessly mannered Gray doesn't manage to pull it off. The unfortunate result is that October Blood -- which does begin with some promise -- becomes as vapid as the world it purports to dissect.

"There's so much to renew in you, such palaces and gardens," says Julian to his bride Paula who "could sense his need to be seized and transported." And here is Gray on Paula's road back from insanity: "My rage at mother's world, at the shrinks, at the devious fops who'd polluted my childhood has abated . . . I'm killing the strumpet who let herself be groomed for the meat market of appearance and approval." If this were rhetoric from a Best editorial, one would assume that Gray was making a satirical point. But this is Paula speaking, Paula, the one seemingly trustworthy observerin the novel, spouting such twaddle.

October Blood is not without its poignant moments. In a sentence, Gray manages to convey the awful confusion of a child forced to grow up in a wholly adult world: "Sometimes when I excused myself to go to the bathroom during a showing, it would be to hide in a dark corner whispering my name, Paul, Paula, to make sure that I existed." Describing Paula's futile hopes that her marriage would be a haven from the world of Best, Gray deftly notes that "she had wanted to be swept away on a long one-way voyage and instead Julian had offered her a round trip."

Still, as Nada Fitzsimmons might have put it: "A dress or two doesn't make a collection." October Blood has a classic theme: a woman coming of age and coming to terms, but its rendering is strictly off the rack.