Muhammad Ali took his tourist's trip of the Soviet Union to the inevitable yesterday - the ring - where he stripped to the waist, rolled down the waistline of his handsome diplomatic blue pinstripe trousers to accommodate his impressive paunch and fired a punch at a determined Soviet face.

The practice glove whistled to a stop two inches from the nose of Igor Vysotsky, a well-known and accomplished boxer here. The young man's eyes tissue and the ringside crowd cheered.

The former world heavyweight champion had just landed another haymaker in his amiable knockout of the Soviet Union.

In slightly less than two days, this most charming and successful of capitalist self-promoters has captured the state-run media and captivated Muscovites in the random man-in-the-street encounters he came here seeking.

He took his quest for "meeting the common people" to Red Square at 6 a.m., jobbing up in workout togs to a line of people queuing for Lenin's Tomb, shook some hands and gave some autographs. Soon, an eager throng had gathered and he clowned and chatted, then jogged off. Monday night, he was mobbed at the circus, a crush so heavy the performance was delayed as hundreds tried for his signature.

Ali has long been held in special regard here for his refusal as a conscentious objector to do military service during the Vietnam war. But officially, Western professional boxing is portrayed as a perversion of athletic purity, pitting men against each other for money paid by sensation-seeking bettors. Boxers such as Teofilo Stevenson, the Cuban Olympic champion, are lauded as true sportsmen.

Whatever the party line, Ali demolished it easily today before more than 1,000 packed into an auditiorium at the Central Institute for Physical Culture and Sports.

"I saw Stevenson fight once," Ali declared. "He's a great three-round amateur boxer. He'd be trouble for two rounds and then I'd knock him out in the third round!" The crowd loved it. "If I box him in Cuba or the Soviet Union, I might let him win. But after I leave here. I'll knock him out." The crowd laughed again as he added that he had come "to see if these Soviet boxers are as tough as they look, because every time they come to America they beat up our boxers."

His public statements here have revolved around three points: a rematch with Leon Spinks, the former marine who took his title in February, a career after retirement from the ring as a kind of international goodwill ambassador, and his own great renown, a subject of unending fascination with him.

He said he would beat Spinks in a rematch, but possibly not by knockout. When he retires, he said, "I'm not sure what I want to do. I want to be a goodwill ambassador for the world and do all I can for peace in the world," which brought him sustained applause. He added that he thought different people could get along easily but that politicians interfered. This remark was translated in such a way as to virtually eliminate its meaning.

Ali, who arrived yesterday billing himself as the world's most famous human, told the audience, "I was surprised to find out how popular I was in the Soviet Union and I want to ask a question: What other Americans - movie stars, athletes - are popular?"

The answers began: Langston Hughes, Mark Spitz, Elvis Presley, Duke Ellington, Louis Armstrong.

Then Ali and his group went downstairs to a gym and soon he was in the ring, doing the familiar clowning that could in time revolutionize the purposeful, humorless quality of Soviet amateur boxers. He mugged, rolled his eyes, glared, clenched fists as laughter burst out.

He went one round with Vysotsky, sweating, grunting, firing fake blows, practicing his glare as the crowd began to understand and laughed. He sparred with four other young fighters and at one point took them all on as the spectactors - avid veteran coaches and their awed young charges - guffawed.

Tomorrow, he heads for Tashkent and Samarkand in central Asia and is scheduled to return here on the weekend, perhaps to fight three exhibition rounds with some local fighters, before returning to the U.S. next week.

There is a report that he may be granted a moment with Soviet President Leonid I. Brezhnev.

All of Ali's public appearances here are being feverishly recorded by an ABC television production team that reportedly paid him $50,000 for the opportunity to accompany him and repackage his tour.