THIRTEEN STORIES AND THIRTEEN EPITAPHS By William T. Vollmann Pantheon. 318 pp. $24

IF William Vollmann's surname were to generate the adjective "Vollmanian" or "Vollmanic," what would his adjective mean? Ambitious, erudite, innovative, sarcastic, impenitently prosaic? Whores for Gloria, The Ice-Shirt and An Afghanistan Picture Show, to name only three of his half-dozen works, would establish at least that; I myself heard him on the radio saying he regarded himself as raw material for things to happen to: an ideal companion for the riffraff he prefers to write about, almost as if he were redoing Kerouac. Just get on the road and see what comes of it.

We used to call that attitude existentialist, intending a philosophical version of what's impromptu, and impromptu Vollmann certainly is, appearing to pull these 13 stories together at the last minute from only distantly prospected materials. The result is a flavor or intonation that implies a feeling about people and phenomena: The random handful is best, and the less studied the writing the better. Certainly, if you were doing an imitation of Vollmann's prose, you would have to include some of his favorite devices -- gaps in typography, asterisks, a sudden drop in letter size, transliterated onomatopoeia ("spoingg!" and "urrrrrrrrrrrrrrrrrrrrrrrreeeeeech!"), and heaps of run-on sentences.

Something callow in this mode of writing suggests that prose should resemble what it describes and not be worked-at, lovingly honed, loaded with a mot juste here and a Nabokovian verbal felicity there. For Vollmann, writing seems impetuous and reflex-like, set down with informal casualness, just so long as there's a lot of it, something so stock it looks like mere typewriting done with a straight face. It reminds me, sometimes, of the work writing students do in their persuasion that fine prose is for others, for wimps and exquisites.

Vollmann has his moments, however, from his opening sentence ("Before I had even gone away, I started polishing San Francisco as if it were a pair of glasses to look through and every new thing dust and dandruff . . .") to the "malignant boom" at the end of the collection. You are suddenly drawn into the world of the story: no preamble, no fanfare. Suddenly what was not going on around you is. Chubby Monique and narrow-faced, serene Vere are feeding each other in a restaurant with the same spoon, and the narrator feels excluded, wanting to see more of them "at home, where among the plump hard pillows of their futon, or condensing on the dark-lobed underleaves of their many houseplants, their innermost tendernesses must live, freshened by a thousand kisses, guarded and protected by the horned ram-skulls that hung on the walls . . ."

Vollmann shines at telling how it feels to be someone, how it feels to want to feel the same as someone; and he does so with ebullient density, seeming to have at hand far more than he needs, endowed with a big helping of the world's contents, as if Balzac were redoing Rousseau or Jules Verne William Burroughs. When someone or something takes his fancy, he goes all the way, ignoring the existence of the paragraph and flowing on into undeniable plenty.

Vollmann also excels at babble and lyrical, sharp-edged interruptions of it. You are glad of "the idiotic self-confidence of the flamingo" on one page because on the next there is a shower of ands as clause structure breaks down. Vollmann tends to repeat himself rather than pin something down in a sparkling epitome. So, instead of narrative moving forward, you get people swirling around in an affable dither, running into one another again and again in Vegas, Belize, Thailand or Gun City -- Elaine Suicide and Abraham Yesterday, dickering about handcuffs, or Abraham and a shrink ("Just as eggnog drips off a blender-blade like mucus from a tonsil, so the shrink's words went pingggg-galplopppp! inside Abraham's mind"). Mr. Yesterday sends his eldest son off to join the Special Forces, where, if he is lucky, he will get to study with Doctor Bacteria, an expert on reducing the enemy intelligentsia to sulphate. Vollmann writes strongly about the godlike pretensions of those who bribe girls with crack; napalm falling and burning; and jungle hunters who arrange a collar of leaves around the cut throat of an animal.

What an acrid, scapegrace world he conjures up, in which nothing matters very much, only a kind of dispirited hedonism, as lax in Omaha as in India, practiced by a cosmopolitan clique whose enervate lives he sometimes graces with celebration. Mostly not, though. His people, as he says, "really are rather rubbery and NEED handcuffs." Or they need watering to make them bloom. Vollmann has an original mind, an intermittent gift for phrasings on which you want to linger, and a massive, awed sense of flux.

Paul West's novels include "The Women of Whitechapel" and, most recently, "Love's Mansion."