By the time Franz Beckenbauer left Bayern Munich to sign a $2.8 million contract with the Cosmos in 1977, he had rebuilt West German soccer along the lines the country's industry and economy were rebuilt after World War II. Sleek. Modern. Successful.

Now Beckenbauer, who came out of retirement this spring to rejoin the Cosmos for perhaps his last season, hopes to make soccer in the United States equally successful before he leaves the game for good.

"Soccer is the most important sport in the world," said Beckenbauer, who will be playing for the New York team against Team America this Friday at RFK Stadium. "In every country they play soccer, and even the smallest nations have a very high standard of play. But this country still doesn't have good soccer."

Beckenbauer's commitment to the development of American soccer is absolute. He operates youth camps in New York and Delaware, and in April appeared before a House subcomittee to urge congressional support of the United States' bid to host the 1986 World Cup. In May, Beckenbauer led a U.S. delegation to Stockholm to lobby the Federation Internationale de Football Associations (FIFA) for postponement of its decision on the site of the cup and for reconsideration of the U.S. bid.

"Maybe now next time it (the World Cup) will go to the U.S.," said Beckenbauer, who led West Germany to three straight cup finals between 1966 and 1974, defeating Holland, 2-1, for the 1974 championship. "Maybe we showed FIFA that the U.S. cares about soccer. Maybe we showed that the U.S. is capable of holding the World Cup."

Beckenbauer, 37, is also enthusiastic about the Team America concept. "It is a very good idea to bring the team together," he said. "It wouldn't work in every country, though. It would never work in West Germany. But Russia has been successful with Dynamo Kiev, which is a national team.

"Team America is a wonderful idea, but it is not the national team," he continued. "(Cosmos players) Ricky Davis and Steve Moyers belong on the national team, but they prefer to play for the Cosmos. You can't blame them. It is their decision."

By the time Beckenbauer came to this country in 1977, he had become one of the best known soccer players in the world. He captained Bayern Munich to an unprecedented three straight European Cup championships from 1974-76 and had won virtually every personal award. To soccer fans everywehere, Beckenbauer was known simply as the Kaiser.

"Beckenbauer is the Kaiser," said Cosmos General Manager Thomas Werblin. "He is the king of soccer."

But Beckenbauer's decision to leave Munich caused turmoil both in this country and in West Germany. Teammates and countrymen pressured him not to leave, and he was offered the job of national coach as incentive to stay. In New York, future teamate Giorgio Chinaglia scoffed at the acquisition of Beckenbauer.

"What is the use of Beckenbauer to us?," Chinaglia said at the time. " . . . Is he going to help us with the crowds? No. He won't draw in this country . . . Investing that much money in Beckenbauer is a bad idea."

But Beckenbauer silenced his critics by joining the Cosmos in midseason and leading them to their first Soccer Bowl championship in five years. Despite playing in only 15 games, he had four goals and 13 points, and was named the NASL's most valuable player.

He was selected the league's top midfielder the next three seasons, and left the Cosmos after the Soccer Bowl victory in 1980. He returned to West Germany and played the last two seasons with Hamburg F.C., then announced his retirement after the 1982-83 season.

Beckenbauer, whose current contract with the Cosmos expires Oct. 15, says he takes the years "one at a time" and won't consider playing in 1984 until after this season. But Werblin says this is probably Beckenbauer's last season.

"I don't think we'll ask Franz to play another year," Werblin said. "But if he decides to keep playing at his current level, we'd love to have him. You can't groom another Franz Beckenbauer. He is one of the great ones. When they come along it is a rarity."