Ring Cycle IT'S TOUGH TO think of art when someone slugs you in the face.    This two-fisted message came home with a jolt to local artists Tom Chapman and Tony Labat last night. They went into the Kezar Pavilion ring to create a "performance piece" of pugilistic conceptual art and ended up in a four-round street fight.    From the moment Labat landed a solid right to Chapman's head, the fey concept of boxing-as-art gave way to animal survival. What began as a let's-put-on-a-brawl-in-a-barn idea turned into a lusty struggle to go the distance. And the crowd that came for some epicene head-thrills got some body-blasts of carnal excitement.    The Labat-Chapman bout was preceded by a card of exciting, elemental contests between professional boxers (two of them women). This mix of off-the-wall and legitimate brought out an audience of stunning variety.    Some of the members of the crowd yelled for blood because they were typical bloodthirsty fight fans. Others called for blood because it goes well with green boxing trunks.    There were beer bellies and pogo pants and orange-streaked hair and bouffants and designer jeans and workboots. Carol Doda, incompletely squeezed into a one-piece silver lame jumpsuit, pranced around the ring holding large signs with the round number on them.    A percussion orchestra of Latina lesbians thundered volleys of rhythm off the arena's tired metal rafters.    It's probably the first time in boxing history that the printed program saluted 124 sponsors, including the Film/Video Department of the Whitney Museum and Electronic Arts International.    The event was billed as "Challenge," and, going in, was a maddeningly amorphous concept. The bare facts are that artist Tom Chapman, a wiry, New Wave type, challenged artist Tony Labat, a stormy-faced guy with dark ringlets of hair, to a fight.

ART RARELY FLOWS from a clenched fist, but there are exceptions. Was Chapman really looking to punch out Labat's lights, or was the challenge itself part of the artwork? Who knows? Who cares?    Everything was happening in quotation marks. Labat and Chapman would "fight." Another two artists, Dan Ake and Richard Simmons, decided to "promote" the fight as their contribution to the piece. Hundreds of fans "bought" tickets, little realizing, or caring, that the act of ticket-buying was just another brick in the wall of creativity.    Another level of reality was added when boxing matchmaker Bill Barros was asked to provide a card of legitimate fights, without quotes. His line-up was excellent, highlighted by a bout between two top-ranked 112-pound women, Louise Loo and Angel Rodriquez, which the lithe and tatooed Rodriquez won by a knockout in the fifth round.    Add a synthesizer band to play the Star Spangled Banner, an old white elephant of an arena, a colorful smattering of grizzled, pug-nosed, cauliflower-eared boxing veterans and you've got, well, you've got what happened last night.    You knew the evening was going to be something different during the National Anthem. One of the trainers reverently stood and removed his false teeth, clapping them to his chest over his heart.    The Loo-Rodriquez fight was punctuated by chants of "Fights for Dykes!" from several female segments of the crowd.    As the preliminaries wound inexorably toward the moment of truth, gladiator Chapman reclined zen-like on his training table, meditating on the shadows of success. Opponent Labat was hopping around his dressing room, just plain old shadow boxing.    It should be noted that these two guys didn't just hop into the ring cold. Both trained for three months, including heavy sparring sessions with real boxers. Labat's sparring was so realistic he needed six stitches to close one practice-round gash.

Nor did these two artists merely come to fight. They both intended to record the experience. Chapman is writing a book, Labat completing a videotape. Labat even plans to sell his red velvet trunks and foot-square sections of his training ring. WARMED BY THE earlier shows of blood, valor and some heavy punching, the crowd set up a throaty roar for the antagonists as they made their way to the squared circle. Competing camps set up chants of "Tony! Tony!" and "Tom! Tom!" as they entered the ring.    Hemingway would have been proud.    Labat clowned a bit as the instructions were given, while Chapman remained cool. Then the bell rang.    The first punch stripped the quotes off "fight." The "event" had turned into something basic, gutsy, and a little scary. The two men's eyes showed that. They hadn't really expected to be scratching for their lives in front of a bawling mob, but they were.    Labat and Chapman forgot all they'd learned in the gym and fought like angry school-kids. Plenty of punches landed, inflicting real pain and punishment.    It seemed to last forever, but only went the scheduled four rounds. Labat kept Chapman on the defensive, and won a unanimous decision form the judges.    In the dressing room after the fight, winner Labat sported two puffy eyes, a bloody nose and a swollen face. He'll feel even worse today. He wasn't talking about art.     "This things started out as a concept thing," he said, his eyes still wild. "But it got very, very serious. I was just fighting, that's all."    Outside the jubilant dressing room, two women met in the corridor. They were the women-friends of the combatants. They looked at one another for a long moment, and then embraced.     "Thank God it's over," one of them said.