The Washington Diplomats' longest week will end today at RFK Stadium when the Cosmos, the lords of American soccer, visit the struggling Dips for a 2 p.m. game.

The game will be nationally televised by ABC, but blacked out in this area. A crowd of 30,000 is expected at the stadium.

For the Diplomats, today's game is crucial. With a three-game losing streak, they need a victory to regain some confidence and self-respect. More than that, a victory over the Cosmos would be, a shot in the arm for a franchise that has yet to come up with a truly major win in seven years of existence.

There will be one lineup change and it is no surprise. Unable to acquire the striker he wanted this week, Coach Gordon Bradley will bench Bobby Stokes, who is without a goal in nine games. His place will be taken by Sonny Askew, who lost his midfield spot two weeks ago.

askew will not play a pure striker position the way stokes does but will probably alternate with Johan Cruyff at moving forward.

"Bobby's just lost his confidence," Bradley said. "It happens to players all the time. he'll get it back eventually but, in the meantime, I think we need a change up front."

The Dips also will be without Juan Jose Lozano, who under NASL rules, must sit out today's game because he received a red [ejection] card last Saturday in Atlanta.

It was that ejection that keyed the Chiefs' 2-1 shootout win over the Diplomats. And it was that defeat that has put the Dips under the gun all week.

First, Bradley and General Manager Andy Dolich made it clear they would not tolerate a 3-6 record and talked of "additions to and deletions from the roster." Then, Madison Square Garden Chairman Sonny Werblin, asked about Bradley's future with the team, hedged, saying, "I don't want to be pinned down."

In spite of the team's record, Bradley appears to be fairly secure at the moment. A victory over the Cosmos certainly would help, however.

It will not be easy.

These are not the talented-but-temperamental Cosmos of the past. This is a team with a 7-2 NASL record and a string of eight wins -- including four exhibitions -- since Hennes Weisweiler became coach a month ago.

The big names remain: Giorgio Chinaglia, playing perhaps the best soccer of his life and leading the league in scoring again; midfielder Franz Beckenbauer, now 34 but still superb; Johan Neeskens, unquestionably one of the best midfielders in the world, and Carlos Alberto, still keying the defense at 36.

There are also new names: Jose [Oscar] Bernardi, Julius Cesar Romero and Bruce Wilson, consistently one of the NASL's top defenders.and there are young Americans: Ricky Davis, last year's sensation, and 18-year-old Jeff Durgan, this year's sensation.

"The only trouble," Weisweiler said, "is trying to keep so many good players satisfied."

Bradley should have such problems. Right now, he has Cruyff back in the lineup after missing the Atlanta game with a thigh problem. Cruyff is almost healthy. He will have Joe Horvath in Lozano's spot. And he is hoping that someone other than Alan Green [eight goals] can find a way to score.

Even playing at home, the Diplomats go into the game as underdogs. They have yet to prove that they can finish their plays and they have yet to prove that they can win a close, well-played game against a good team.

"We haven't broken through yet," Bradley said. "We've been a good team at times, but not consistently. We need a big win to get out confidence back. The players know we have talent; they need to know that we can win."

Against the best opposition they have faced this year -- Tampa Bay and Fort Lauderdale -- the Dips have produced outstanding performances. But each time, they also lost. Each time, the other team made the deciding play.

To a degree, this is a continuation of a pattern set last year. The Diplomats played excellent soccer in both their meetings with the Cosmos but still lost, both in shootouts. They played well at Tampa Bay, but lost, 1-0, on a goal in the final minute. They staged a marvelous comeback in their RFK playoff game against Los Angeles, tying it in the last three minutes while playing a man shy. But still they lost -- to Cruyff -- on a goal in overtime.

Considering the fact that the Dips have never won a playoff game, the support the team has received in the area is remarkable. Today's growd will be further evidence of that.

The Dips need a breakthrough. Management says if it is not today, it will come later this season. But no other single game can provide the kind of impetus this one can, especially with the Cosmos playing so well.

"This team is going to come through before the season is over," Bradley has said all week. Today would be a good time for his players to begin making good on that promise.