T. Coraghessan Boyle was between acts, just finished with an appearance on "Late Night With David Letterman" and getting ready for a reading at Columbia University.

A born performer, he fit right in on Letterman, telling jokes about his middle name, crocodiles in Georgia and unsavory food in Japan. The host played it straight and let his guest steal the show.Letterman isn't known for trading barbs with men of letters - imagine one-liners with John Updike about "Rabbit at Rest" or Gabriel Garcia Marquez on "One Hundred Years of Solitude." So how did Boyle end up sitting beside him?

His appearance is one reason. Boyle doesn't look like a writer. He stands 6-foot-3, his skinny frame covered by a dark gray suit with white speckles and anchored by red high-top sneakers. He has kinky hair, the color of bruised apricots, and a matching beard.

And the cover boy of The New York Times book review section doesn't act like a writer, certainly not the kind who spends hours brooding about the future of minimalist novels or the crisis of middle-class relationships in the late 20th century.

Just call him, in the Letterman spirit, "The World's Most Dangerous Author."

"I came up from nowhere, looking at TV all day long and thinking writers were snobs," Boyle explained in an interview at Manhattan's Algonquin Hotel, where brooding authors are known to congregate. "But I have the credentials. I have the Ph.D. I have books on the front page of The New York Times.

"I think some writers who don't have the credentials have to prove themselves by acting stuffy. Maybe I've been lucky. I've never been part of the club and I never will and I have no problem with that."

Seven books and the PEN-Faulkner Prize for fiction in 1988 have settled him only slightly. Boyle is a hard man to pin down. He's a fabulist, a personality, the slippery "I" in a hurricane of literary adventures.

Read his short stories, "If the River Was Whisky" and "Greasy Lake," or his new novel, "East Is East" (Viking, $19.95), and you'll find apes, chefs, musicians and the wife of Nikita Khrushchev; the author is distinctly off the pages.

None of the characters in "East Is East" is based on people he knows. He's never lived in any of the locations. The plot came from a newspaper article he lost long ago.

What does T. Coraghessan Boyle, recovered addict of the small screen and other vices, have to do with this wacky tale of Hiro the Japanese sailor, who jumps ship along the coast of Georgia and dodges immigration officials in the Okefenokee Swamp?

"My joke is I wrote a novel about Georgia because I had flown over Georgia several times on my way to Miami. It's easier to write the book if you've seen the place, but I don't have to go there like James Michener and dig in. I think fiction is supposed to be an exercise of the imagination. My take is I can do anything I want."

He was born 42 years ago in his idea of nowhere: Peekskill, N.Y., the childhood setting for the author and his television set. The transformation from Tom Boyle, couch potato and daydreamer, to author T. Coraghessan Boyle (the middle name is an early work of fiction) began at a creative writing class in college.

Boyle calls himself a "virgin" to writers' colonies, but he did spend five years at a den of iniquity known as the Iowa Writers Workshop, where Kurt Vonnegut, John Irving, Flannery O'Connor and many others came of age.

Boyle expresses his feelings about the company of his peers in "East Is East," which features a colony swarming with pesky authors:At breakfast, it was thought, artists of a certain temperament required an absolute and meditative silence, broken only perhaps by the discreet tap of a demitasse spoon on the rim of a saucer - in order to make a fruitful transition from the realm of dreams to that exalted state in which the deep stuff of aesthetic response rises to the surface.

Others, of course, needed just the opposite - conviviality, uproar, crippling gossip, lame jokes and a whiff of the sour morning breath of their fellow artists - to settle brains fevered by dreams of grandeur, conquest and utter annihiliation of their enemies."Of course, I was Olympian and far above all that pettiness," Boyle, speaking of his days at Iowa, said with a laugh. "I know how it feels, and I think that's where I'm getting some of my inspiration. I didn't do any politicking and I got everything I wanted from pure virtue, like Mahatma Gandhi."

"Descent of Man," a collection of stories written for his doctorate at Iowa, was published in 1979. He followed that with more stories, "Greasy Lake," and a pair of novels, "Budding Prospects" and "Water Music." The historical novel "World's End," set in the New York town of "Peterskill," won him the PEN-Faulkner award.

For the Columbia reading, Boyle keeps the sneakers and dons a snappy black jacket. This audience will have read his books, but for the author it's still a performance. Boyle sees himself as a crossover artist, straddling talk shows and the Ivy League.

"I do believe the way everything is constructed with television and personality, writers have to go out and grab hold of the attention in some way," Boyle said.

"I think I wonder where I fit in exactly, but as far as being on the front page of The New York Times and also being on `David Letterman,' I have no problems with that. I think in this society you have to try to catch and recapture the audience for literature. That's a lot of energy spent for things outside of writing, and that's bad."