In spite of the humidity that blanketed RFK Stadium yesterday, Cosmos glided smoothly through a one-hour workout. As Giorgio Chinaglia, Franz Beckenbauer, Julio Romero, Francois Van der Elst and Jeff Durgan bounced around the field, Tom Werbin stood in the press box and watched.

Werblin is the Washington Diplomats' vice president in charge of operations. He is also a former Cosoms employee and the youngest son of Madison Square Garden President Sonny Werblin. After a few minutes of observation, Werblin turned away from the practice and said, "They are just so good."

The Cosmos are good. Individually, they probably have more talent than in 1977 and 1978 when they were Soccer Bowl champions. More important, they are not dependent on their individual skills to survive. Unlike past Cosmos teams, they compete with the opposition, not with each other.

"You have to give (Coach) Hennes Weisweiler all the credit in the world for the way we have played this year," said Giorgio Chinaglia. "For the time in my five years here we are truly a team. We play together, not just as individuals. There is no comparison between this team and the Cosmos teams of the past. The difference is unbelievable."

One of the biggest differences is in goal. In the past, Cosmos goalies succeeded because the rest of the team was so strong, although Jack Brand had some outstanding games in the playoffs in 1978.

But this year, the goalkeeper, German Hubert Birkenmeier, is a star. He has played every minute of every game, recording a 1.14 goals against average during the regular season, 1.42 in the playoffs. Birkenmeier's outstanding play has finally ended the Cosmos game of "who is the goalie this week."

He makes us better as defenders," Jeff Durgan said, "because we know if we make a mistake, he can save us. That takes alot of pressure off us."

If Durgan, the 19-year-old rookie of the year, feels pressure, he doesn't show it. He has marked the other teams' top strikers all year and will probably draw the Strikers' Gerd Mueller in Sunday's Soccer Bowl. It hardly phases him.

"I feel like I have an advantage against anyone I play, because I'm younger than they are," Durgan said. They may have more experience, they may have some tricks I don't have but I've got an awful lot of desire. You can do a lot with desire."

Desire has never been very big with the Cosmos. Pure talent has always been their trademark. And, in spite of the presense of players such as Durgan, steady Canadian Bruce Wilson, and superb defenders Wim Rijsbergen and Carlos Alberto, the heart of this team still lies in the two central figures: Chinaglia and Franz Beckenbauer.

Chinaglia, by his own admission, has been amazing in the playoffs with 16 goals in six regular games and one minigame. He has had perhaps his best season in the league with a 32 regular season goals and a league-leading 77 points.

Beckenbauer turned 35 last week. He has never like playing midfield and his work rate -- or lack thereof -- has been criticized at times since he first arrived here in 1977.

But Sunday is expected to be his last NASL game (he will play in Germany next season) and it is in the big games that Beckenbauer is at his dominant best. If Chinaglia is the Cosmos hit-man with his ability to score at anymoment, then Beckenbauer is their catalyst because he can control the flow of the game when he is right.

"In a game like this I would bet that Franz will have a major effect on the outcome," said Diplomat Coach Gordon Bradley, Beckenbauer's first coach with the Cosmos. "In one game, for 90 minutes, I bet on him to come up with the big play when things are tighest."

Beckenbauer, shy and withdrawn when he first arrived in the U.S., has loosened up considerably as he has become more comfortable with the language and hs new surroundings.

"All year, I think every member of this team has felt there was something to prove because we did not make it to the Soccer Bowl last year," Chinaglia said. "We thought we were the best team.

"Sometimes you have to lose to realize haw much winning means to you, to remember how much fun it can be. We did that.Now we know. We want to win."

They want to win to have fun. They expect to have fun Sunday. After all, they are SO good . . .