Mike Weaver punched out a message tonight on the television tape recorder in Muhammad Ali's home in Los Angeles: "Are you sure you want to make a comeback?"

The muscular thumper from Los Angeles spotted John Tate 24 1/2 pounds, a big lead in points, and knocked him out with 45 seconds left in the 15th round for the World Boxing Association heavyweight championship.

A right to the belly, in Tate's corner, appeared to paralyze the 232-pounder from Knoxville momentarily.Then a left and right sent him sagging face forward to the canvas. Referee Ernesto Magana Ansorena of Mexico counted 10 over him and could have made it 110.

Tate lay there several minutes and a stretcher was brought to the ring. It was not used, but oxygen was given to the fellow who had gone unbeaten in 20 professional bouts.

Tate was so stunned by the final punches that his handlers had to carry him from the ring. He was helped to his dressing room, barely able to keep his feet, by four of his entourage.

Dr. Robert Whittle, Tate's physician, when asked by ABC's Keith Jackson about the fallen champion's condition, said Tate had suffered a mild concussion with the knockout.

Weaver, who almost took Larry Holmes' World Boxing Council championship in June before being knocked out in the 12th round, was so joyous he leaped in the air, fell to the canvas and suffered a facial cut rolling around in glee, not far from the prone Tate.

Weaver is in line for the big-money shot at Ali this summer in New Orleans, if he wants to risk his WBA title right away.

All three officials had Tate ahead. Referee Magana Ansorena scored it 138-133, judge Nicasio Lorenzo Drake of Panam, 137-134, and judge Cesar Ramos of Pureto Rico, 136-133.

There were no other knockdowns.

Tate suffered a cut in the corner of his right eye in the fifth round and Weaver probed at it, but it became no factor because Tate's corner stopped the bleeding thereafter. Weaver's left eye reddened in the fourth.

The champion, making his first defense, took command early and seemed to have the fight in hand, when he had his biggest round, the seventh. He answered a left-right-life combination by the challenger with a buzz-saw attack to the body and suddenly switched to the head. Yet, Weaver was countering with left hooks at the bell.

It was in the 12th that Weaver abandoned his caution and struck dread into Tate's hometown fans for the first time.

The second of two curling left hooks staggered the 6-foot-4 champion, a follow-up right to the head took away Tate's poise, and the crown of 12,769 tried to rouse him by chanting, "Big John Tate . . . Big John Tate."

Weaver kept hooking and putting together multi-punch combinations before the bell gave the tiring champion a much-needed respite.

Weaver, 207 1/2 to Tate's 232, appeared to appreciate a slowing of the action in the 13th as much as fleshy Tate.

It was Tate doing the holding in the 14th and Weaver complaining. The challenger was warned about a low blow and Tate about holding Weaver's head in one hand and punching with the other.

Now it was Weaver snapping off a slick one-two combination and Tate holding again. He drove Tate into the ropes with a left hook to the stomach just before the bell.

Weaver sprang off his stool at the start of the 15th round, flailed Tate to the head and body and Tate clinched desperately, in the manner of a wrestler.

As the round wound down, Weaver trapped Tate in his corner, and among several punches inside, sank a right hand into the champion's flabby midriff. Tate seemed transfixed by the effect. As a left whistled to his jaw, he tottered forward and then sagged face down, the classic results of the properly delivered body blow.

The referee counted deliberately, probably because he saw there was no movement from the face-down champion, and the official crossed both hands, palms down, to signal the finality of it all.

Tate's manager, Ace Miller, clambered into the ring and tried to turn over Tate by the neck and shoulders but was not built for it at 5 feet 6 and about 150 pounds. With assistance it was accomplished by there still no movement from Tate.

"He was unconscious for about 2 1/2 minutes. I gave him 'pearl' (a capsule of spirit of ammonia) to revive him," said Whittle, who had been disqualified from working as the Tennessee Athletic Commission doctor because he is Tate's personal doctor.

Tonight's victory was Weaver's 21st and his 14th by a knockout. In his previous 29 bouts he was floored by Holmes and by such as Howard Smith, Billy Ryan, Larry Frazier and Duane Bobick.

Tate had scored 16 knockouts in going unbeaten in 20 bouts. Bobick was among his knockout victims, in the first round.

Tate's physician noted that his patient "had a cut above the right eye and a small cut below the left eye." He added that Tate "was lucid afterward but disappointed." He said he would keep him under observation overnight after the right eye was treated at Baptist Hospital.

Weaver said, "I knew I was behind on points; they (his corner men) told me I had to knock out Tate to win it. I gave him a real hard right to the body and then my best left hook, and that did it. Tate was getting tired of my body punches. I really hurt him in the 12th. I think he got disgusted, but I was getting tired at that point.

"I'll fight Tate again, but not in an immediate rematch. All I heard before this fight was how Tate would fight Ali. Ali has always been my idol. I love the man and respect him. But I'll fight him and beat him, and then fight Holmes (to become undisputed champion).

"Tate gave me a harder time than Holmes did. He made the mistake of trying to come in and outslug me.I think the crowd cost Tate the fight with all that yelling. That is why I don't want to fight in my hometown (Los Angeles).

Enough for now that Weaver, the man with the Greek-statute physique, substantiated his nickname of "Hercules."