Muhammad Ali, five weeks short of his 40th birthday, lost tonight to the invisible opponent who is undefeated now and always.

"I couldn't beat Father Time," Ali said, after losing a unanimous decision to a mediocre Canadian who a decade ago could not have carried Ali's gloves. On two officials' cards, Trevor Berbick lost only one round as his agressive, if inelegant, pursuit of Ali ended the three-time heavyweight champion's career.

"This is it," Ali said.

He did not oject to the decision. The judges' scoring was Clyde Gray, 99-94; Alonza Butler, 97-94, and Jay Edson, 99-94

He lay on his training table. His twin daughters, 10 years old, wept. His wife, Veronica, stood in silence.

Someone said to Ali, "Six months from now, Muhammad, will you smile at us and say you were only kidding about 'This is it?' "

Ali said, "No, it's too late now. The body can't do it any more."

That was painfully clear to the Ali loyalists in the crowd of 7,000 in a makeshift "stadium" of 11,000 folding and wooden bleacher seats. They came to see Ali try a step toward what he said would be a comeback for an unprecedented fourth heavyweight title.

After the one-sided decision was announced, many fans simply rose to their feet in silence -- not angry, not surprised, just in tribute to the end of 21 years of unmatched drama.

Ali never had a chance tonight. He was not the harmless statue of 14 months ago when he was humiliated into "retirement" by Larry Holmes. Tonight Ali moved some, threw enough punches to win, and took every hard punch Berbick wanted to throw.

But Ali's punches were feather dusters. In the first three rounds, he often launched left-right combinations. Clearly, Berbick was unfazed by any of his punches. The 28-year-old Canadian champion, an aggresive, roundhouse, swinging brawler who now has a 20-2 record with 16 knockouts, carried the fight to Ali after those earlier rounds.

Ali's strategy was to stay in the center of the ring, where he could use his jab and keep Berbick off him. Perhaps that way he could work his magic on the judges, who in the past have treated Ali kindly. Berbick was worried about going the full 10 rounds with Ali, afraid the officials would give the fight to Ali if he stood at the end.

Instead, Berbick finally moved Ali out of ring center and continually trapped him against the ropes. Ali was helpless there. By the fourth round, Ali, who weighed 236 1/2 pounds, was a fat old man, slowly trudging to his corner between rounds to rest his weary bones.

As Father Time took its payment from an old man trying to be young, Ali found himself in full retreat. His jabs were barely noticed by Berbick. His right hand, delivered with the familiar sneer of the past, was nothing but a tap on the noggin for Berbick. His strength waning, Ali could not move Berbick off him when the kid caught him on the ropes.

So Ali, as wise a ring tactician as the heavyweight division ever saw, went to his memory bank for a trick. He reached back to 1974, in Zaire, when he regained the championship he first won in 1964. Back then, he knocked out George Foreman by inducing him into exhuastion. It was the rope-a-dope strategy, in which Ali simply allowed Foreman to punch himself out while Ali lay against the ropes.

"He tried to do me like he did Foreman," Berbick said. "He wanted me to get worn out. But I didn't let him do it."

After a burst of four or five punches, Berbick would move away and set up for battle another place.

Never a fighter with finesse, Berbick needed none tonight. All he had to do was force the action. After Ali's feeble love taps of the first three rounds, Berbick saw no danger and advanced on Ali at will. In the fourth round, a sweeping left to the ribs bent Ali sideways. It was at the end of that round that Ali slumped heavily onto his corner stool.

Much of Ali's sway over judges has been the product of round-ending furies, but tonight, from the sixth round on, Berbick closed every round with three or four punches Ali could not stop.

Although the outcome was inevitable after seven rounds, the crowd refused to acknowledge it. As they had chanted, "Ali, Ali," when he first walked to the ring set up behind second base on a kids' baseball field in the chill winter air of an island in the ocean, they sought to raise up Ali in the eighth. For it was then, for the only time tonight, that Ali began to dance.

Up on his toes, circling the stalking Berbick, Ali seemed again the floating butterfly who had won 56 times and lost only four. The crowd loved it. But from Ali's corner came the familiar thunderous voice of his longtime friend, Bundini Brown. "You gotta throw some punches," he said.

Ali couldn't do it. Berbick stopped the dance with a hook to the ribs. Even in the 10th round, when Ali knew he needed a knockout, it was Berbick who finished the fight by rocking Ali with three punches at the bell.

Ali was 39 years old and getting older every second.