Middleweight boxer Willie Classen, who underwent brain surgery last Friday night after being knocked out at Madison Square Garden's Felt Forum, died tonight without regaining consciousness.

Classen, a 159-pounder from Puerto Rico, had taken an eight-count with 15 seconds remaining in the ninth round against unbeaten Wilfred Scypion of Houston at Madison Square Garden. When the bell sounded to start the 10th and final round, Classen, 29, remained on his stool.

However, Classen's handlers, headed by manager Marco Minuto, lifted him from his seat and rushed him out of the corner. Classen never raised his hands and was hit twice with rights by Scypion, 156.

Referee Lew Eskin stopped the fight at 12 seconds as Classen lay flat on the ring outside the ropes. He was carried away on a stretcher and taken to Bellevue, where he underwent 2 1/2 hours of surgery Saturday morning.

Classen was stopped in a bout in London less than a month ago.

Dr. Richard Izquierdo of the New York State Athletic Commission said he talked to Classen both in Spanish and in English between the ninth and 10th rounds and that the Santurce, Puerto Rico, boxer said he was all right and wanted to continue.

"I happen to be Willie's personal doctor," Izquierdo said the night of the fight. "I would never let him continue if I didn't think he was fit."

"The doctor said he could continue and the manager said he could continue," said Eskin, a veteran referee. "I told the manager, 'i don't want to hear from you. He's the one getting hit.' So I asked the fighter, 'you all right, Willie? You want to continue?' He said yes. He was coherent. He was talking to me.

"Anyone could have halted it, so if there must be blame, all must share it."