Kiko Bejines, a 22-year-old Mexican fighter who was knocked unconscious Thursday night in the 12th round of a bantamweight title fight in Los Angeles, underwent 3 1/2 hours of surgery yesterday at Los Angeles County-University of Southern California Medical Center to relieve pressure caused by swelling from a contusion of the brain.

Bejines, breathing with the aid of a respirator and still unconscious, was reported in critical condition by a hospital spokesman after what was described as a "last-ditch effort" to relieve the brain pressure and stem hemorrhaging.

Hospital spokesman Tony Tripi said the team of three neurosurgeons might have to remove part of Bejines' injured brain.

Bejines was the World Boxing Council's third-ranked bantamweight fighter.

He was injured in the WBC title fight with Alberto Davila at the Olympic Auditorium. The boxers were fighting for the title left vacant when Lupe Pintor was stripped of his title for being unable to defend following a motorcycle accident earlier this year.

Davila started a series of punches at the opening of the 12th round that staggered Bejines. Then, 33 seconds into the 12th round, Davila landed a hard left-right combination on Bejines' chin. Bejines toppled backwards and was counted out.

Briefly, Bejines regained consciousness and tried to get up, but he lost his balance and fell again. Semiconscious, he was helped to his corner by his trainers where he collapsed and lost consciousness once again.

After repeated attempts to revive him with ammonia capsules failed, Bejines was carried from the auditorium on a stretcher and rushed by ambulance to California Hospital. From there he was transferred by helicopter to the L.A. County-USC Medical Center.

Dr. Bernardt Schwartz, the ringside physician at Olympic Auditorium, said Bejines was "in very bad shape" just after the fight, according to United Press International. "His pupils of both eyes were fixed and dilated," Schwartz said. Schwartz was at ringside at Olympic Auditorium two years ago when a Welsh fighter, Johnny Owens, was badly beaten in a title fight against Pintor and died weeks later without regaining consciousness. Schwartz said Bejines appeared to be in similar condition to Owens as he was carried from the ring.

Last year, Korean boxer Duk Koo Kim died after being knocked out by Ray (Boom Boom) Mancini during a fight in Las Vegas.

Referee Waldemar Schmidt, working his 46th title fight, said, "This was by far the worst condition I've ever seen a fighter leave the ring in. I didn't think he was badly hurt at first. It surprised me when he couldn't lift his gloves off the canvas when he was trying to get up."

Bejines, of Guadalajara, is one of three boxing brothers who have built a large following in the Los Angeles area. Until the 12th round, Thursday's bout had been close, with Bejines leading on two of the judges' cards. The third judge scored it even.

Thursday's fight was Bejines' first after a year's layoff. He last fought in August 1982 when he was defeated in a fourth-round technical knockout by Edgard Roman.