Cuba's Teofilo Stevenson won the Olympic heavyweight boxing championship for an unprecedented third time today, scoring an unspectacular decision over a pug-faced Soviet, Pyotr Zaev, to assure that the brass band would play the Cuban national anthem for the sixth time in four hours.

Cuban fighters won medals in 10 of the 11 Olympic weight classes, including the six golds. Four years ago, at the Montreal olympics, Americans won five golds and seven medals overall, while the Cubans won three golds and eight total medals.

Stevenson, 28, won his 11th consecutive Olympic bout, successfully defending the championships he won at Munich in 1972 and Montreal in 1976. But he was not nearly as impressive as his countryman, Jose Gomez, who won the middleweight gold and reinforced the impression that he is, pound for pound, the best amateur boxer in the world.

Finals in boxing, canoe and kayak, soccer and judo wrapped up the last full day of competition in the controversial Moscow Games, which were boycotted by the United States and approximately 50 other countries to protest Soviet military aggression in Afghanistan.

In the soccer final, reserve Jindrich Svoboda scored with 13 minutes left to give Czechoslovakia a 1-0 victory over defending champion East Germany. A rain-drenched crowd of 80,000 in Lenin Stadium watched the rough match, in which one player from each team was ejected.

Only the equestrian individual jumping competition remains before the Olympic flame is extinguished in closing ceremonies Sunday night.

Soviet athletes have won 80 gold medals in the games, which suffered competitively from the absence of teams from the United States, West Germany, Japan, Canada and China among others, but the boxing finals turned out to be something of an embarrassment for the hosts. Soviet fighters lost six of seven finals, four of them to Cubans.

"The Soviets are going to recall their coaches form 'The Free Island,' as they call it," commented one ringside cynic. "What's the Russian phrase for 'Bad Day at Black Rock?"

Stevenson, the 6-foot-5, 220- pound Cuban national treasure who looks like a classic sculptor's depiction of the perfect athlete, won a 4-1 decision over Pyotr Zaev, 5-10 and 190, a stubby mutt of a man with a nose that combines the profiles opf Jimmy Durante and Cyrano de Bergerac.

In his red trunks and vest, the muscular Zaev looks truly like an animated fireplug. He kept battling, but Stevenson's enormous 84-inch reach gave him an insurmountable advantage.

Most of the time, Stevenson kept flicking the harmless left jab that American John Tate -- a knockout victim of Stevenson's thunderous right in the semifinals at Montreal -- calls his "steering wheel."

Zaev kept lunging forward with looping rights, trying to get inside, but Stevenson kept him at bay except for one flurry of three rights late in the second and another brief rally in the third.

Stevenson never was able to "steer" his opponent into the path of the straight right that has won him so many fights, and has kept him undefeated in major international competition since the 1971 Pan American Games. He did land one good right uppercut in the third round, but it was on balance a dull fight.

"I think we've seen Stevenson past his best," said Henry Cooper, the former British heavyweight who once floored Muhammad Ali in a title bout. Few would disagree. Perhaps not even Stevenson, who has said he will probably fight two more years and then retire.

The fiercely pro-Soviet crowd of 18,000 spectators at the Olympic Sports Center chanted "Za-ev, Za-ev" during the bout, and immediately afterward, when their hero threw up his hands and broke into a huge smile.

He appeared happy just to have finished the bout. Stevenson had won nine Olympic fights in a row in less than the three-round distance until the semifinals here, when Hungarian Istvan Levai backpedaled for nine minutes in a self-protective retreat.

Zaev at least took the fight to Stevenson, and most of the partisan spectators had willed themselves into believing the hometown lad had won. They were stomping and chanting a cheere that sounded suspiciously like "block that kick," and they jeered Stevenson derisively when he raised his arms in a triumphant salute before the decision was announced.

Judges from Nigeria, Austria and Mexico scored the bout 59-58 for Stevenson. An Algerian had Stevenson ahead, 60-57, and a Nicaraguan made it 59-58 for Zaev.

Stevenson, the ultimate athletic symbol of Fidel Castro's Cuban revolution, postponed a postmatch press conference until Sunday, but is expected to announce that he will not go for a fourth Olympic gold medal at Los Angeles in 1984. He reportedly is weary of boxing, and ready to pursue a career in politics. He was elected to the Cuban National Assembly in 1976, representing his home district of Las Tunas.

Stevenson is the first boxer ever to win three Olympic gold medals in the same weight class.

Laslo Papp, who was in Moscow as coach of the Hungarian team, was the only previous triple gold medalist, winning the middleweight title in 1948 and the light middleweight crown in 1952 and 1956.

Stevenson has stressed after his previous Olympic victories that he is a product of the Cuban national sports system and has no desire to fight professionally, "I will always be an amateur. I am happy as I am," he has said repeatedly.

It was painfully evident on finals day that this Olympic boxing tournament missed the boycotting countries -- particularly the United States, which regularly has won its share of boxing gold.

It was difficult for Americans to work up much enthusiasm, for example, for the light heavyweight final in which Yugoslav Slobodan Kacar outpointed Pawel Skrzecz of Poland.The most interesting aspect of the unpronounceable bout was that the referee banished all three seconds from Kacar's corner for shouting advice to him during the fight, against international amateur rules.

Cuba lost the first of five finals against the Soviet Union, Hipolito Ramos dropping a narrow decision to Shamil Sabyrov in the light flyweight final. The Cubans then won all the rest, to the chagrin of the Soviet crowd that whistled the Cuban winners when they mockingly blew kisses after their triumphs.

Armando Martinez, a windmill who bores forward like Joe Frazier and should be nicknamed "Smokin' Armando," set the tone by pummeling popular Aleksandr Koshkin in the light middleweight final.

Angel Herrera of Cuba was the only fighter other than Stevenson to repeat his 1976 gold medal performance. He won a rough and ugly brawl for the lightweight title over Soviet Viktor Demianenki, who went to the canvas once on a cross-body block. The referee stopped the bout when Demianenki's right eye, cut in an earlier bout, closed in a red and puffy mess.

The most stylish performer was Gomez, who decisioned Viktor Savchenko of the Soviet Union in the middleweight final. Gomez is quick, slick and a devastating puncher. He knocked down Sachenko with a straight right in the first round, floored him again in the second and had him exhausted, hanging on and wobbly at the final bell.

Savchenko is another favorite of Soviet boxing fans, who have never seen professional prize fighters. They were chanting his name today at the start, but Gomez thoroughly whipped him.

Does anybody know the Russian phrase for "Queer Street?" It would have come in useful today, because that's where the tough Cubans were sending their nonplussed hosts.

A peculiar competitive end to these troubled and Soviet-dominated Moscow Games.