BIG-CITY BYLINER

For nearly four decades, Damon Runyon was America's liveliest columnist and a New York celebrity who virtually invented the romance of the Roaring Twenties and the illusion of Broadway. By turning a few dozen hoodlums and speakeasy dancers into the lovably dishonest ''guys and dolls'' of his short fiction, he made a fortune, lived the high life, inspired 26 movies, a great musical, and the adjective Runyonesque. Still, he was pretty much of a louse, a man who treated his first wife and kids like chattel, took enormous glee in the fleecing of suckers, and winked broadly at murder. Jimmy Breslin wants you to know all that in Damon Runyon (Ticknor & Fields, $24.95). Breslin is no shill for the colorful character. Even he can't resist calling the guy an ''unreliable bum.'' So why such a massive biography? ''Because,'' says Breslin, ''more than anybody else I've ever heard of, he beat the New York newspaper business. Beat it to a pulp.'' Besides, it's a great story. Born in 1880 in Manhattan, Kan., Runyon was a classic case of the American hustler who makes himself up as he goes along. Christened Alfred Damon Runyan, he changed the spelling of his last name-most likely to disassociate himself from his much-hated father-then dropped his first name when an editor told him that ''Damon Runyon'' happened to be a good-looking byline. And his byline was something that Runyon, who'd been a reporter since age 15, cared about fiercely. In New York, at Hearst's morning American, he worked the sports beat, but since the world of sport and the world of crime were so often indistinguishable, Runyon and his portable typewriter spent as much time parked in Broadway saloons as they did at the ball field. He gave up drink, but he listened and he watched, and when he finally turned to fiction, he distorted shamelessly, turning New York's seedy midtown into a kind of underworld Oz, and transforming thugs like Frank Costello and Owney Madden, Arnold Rothstein and Arthur Bieler into Dave the Dude, Nicely-Nicely, and Nathan Detroit, ''fine, upstanding dishonest people who fell in love,'' says Breslin ''often to the sound of gunfire.'' By the 1940s, most of Runyon's old pals had been murdered, World War II was changing the dynamics of Manhattan, and his era had passed. Abandoned by his second wife-the preposterous Patrice, who'd grown up on the streets of Juarez but claimed to be a Spanish countess-and then stricken with throat cancer, Damon Runyon died in 1946. Appropriately enough, his ashes were scattered over Times Square. Breslin freely concocts dialogue to enrich an anecdote (much of the material, he says, comes from ''a thousand conversations'' he heard about Runyon). Nonetheless, the author has whipped up an irresistible entertainment, a barroom biography bursting with ego (Runyon's and Breslin's) and crammed full of social history, newspaper lore, and urban comedy. But is it true? Who knows? Who cares? If it didn't happen exactly this way, it should have. A

EXCERPT MORE EQUAL THAN OTHERS The first time Damon Runyon went to City Hall was in 1915, for a meeting with a state senator from Greenwich Village, James J. Walker, to discuss a bill that would legalize professional prizefighting in New York. They met in the lobby, standing behind a pillar for privacy. Walker, who regarded himself as a songwriter, had a hoarse voice from singing new songs through most of the night before. He never wrote the songs. As he was well known enough to get a song published, he only had to hear a tune by some busted-down guy who didn't have what to eat, and if Walker liked it, for a few dollars on the piano top he could say it was his. Walker then convinces himself that he had written every American song since the national anthem. Of course he was the right guy for Runyon to approach about getting a boxing bill introduced. They spoke for about two minutes in the marble lobby when Walker said, ''I hope between your Hearst papers and the Democratic Party this can get done.'' ''I am not a Democrat,'' Runyon said. ''I am a Communist. I believe in sharing the wealth equally. If fight promoters make money, I am the first on line to collect.'' ''How is it equal if you're first on line?'' Walker said. ''Because after me everybody else comes first,'' Runyon said.