For the Washington Diplomats, the next two days are for basking in the glow of vindication.

Labeled -- by themselves -- as a team that quit when things got tough, the Diplomats played perhaps the guttiest game in their seven year history. They also earned their biggest victory in those seven years Sunday, a 2-1 shootout triumph in Giants Stadium over the Cosmos.

They beat the Cosmos in a game that meant something to the lords of the NASL because they still are fighting Seattle for the best record in the National Conference.The Dips beat them when it appeared that a questionable referee's decision, awarding the Cosmos a penalty kick, might have cost them the game.

"When they scored the penalty kick (for a 1-0 lead), they thought the game was over," Coach George Gordon Bradley said. "They relaxed at the back for a second and we took advantage of it right away."

Perhaps tying the game was more significant in terms of the future than the 4-2 victory in the shootout. A shootout is something of a lottery where luck often decides the outcome as much as skill.

But coming from behind when the other team has gone ahead with less than six minutes left is a feat the Diplomats had accomplished only once all season. In fact, the other three shootouts they were in -- all losses -- were in games they led in the second half.

"We've been playing better and better the last few weeks," Bradley said. "This was coming. We played well in Minnesota and Vancouver and lost. We didn't get any luck. Tonight maybe, we finally got some luck."

For Bradley, it was a special night. Removed from the Cosmos coaching job in 1977 with the team in first place, he had suffered through five losses, three of them in shootouts, to his old team.

On Sunday, he came into their stadium and beat them when they were 14-0 at home on the season and badly needed to win.

'That's what makes this special for me," said jubilant Diplomat President Steve Dansansky. "This is just great for Gordon. He's worked so hard to bring us this far. He's been through a tough season and never blinked. Now, we seem to have it licked."

The Diplomats are 15-15 for 141 points and have clinched second place in the National Conference East and a playoff berth. They have two games remaining, Wednesday at RFK against New England and Sunday at RFK against Minnesota.

Then comes the playoffs, probably a first-round rematch with Los Angeles, the first game in Washington Aug. 27, the rematch and a minigame, if necessary, in the Rose Bowl Aug. 30 or 31.

The questions now are these: can this team, which has never won a playoff game, finally advance through the first round? Was Sunday a one-night wonder or was it part of a trend? Have John Cruyff, Bradley and the others put aside their personal differences to concentrate on soccer?

"This reminds me of the '76 season with Toronto," said Carmine Marcantonio, rembering the championship team of that year. "We struggled early, we had a superstar (Eusebio) who fought with the coach. Then, slowly, we put it together towards the end of the season and went all the way with the playoffs. I think we can do that here, too. I think we're going in that direction."

"We are doing better, that should be obvious," said Cruyff. "We're creating chances; we're running to the open spaces. We're a better team."

But before Sunday, the Dips were creating chances, running to the spaces and coming up short when it counted most. Now, they have gone that extra step, perhaps the toughest step of all. They have won on a night when the other team was as good, perhaps better for 90 minutes. That hasn't happened before.

"We've always known we were capable," said Bradley. "But knowing you're capable of winning and actually winning are two different things. Now, we've won. I think we'll win some more before this season is over."

Among the Dips' walking wounded two players, Thomas Rogan and Juan Jose Lozano, caused concern yesterday. Rongen has a severely sprained ankle and probably is out for Wednesday, questionable for Sunday. Lozano may have chipped the calf muscle in his right leg again and his status is questionable for an indefinite period . . . Tickets for the playoffs went on sale yesterday at all Diplomat ticket outlets. The opener will be Aug. 27 at 8 p.m.