After playing near flawless soccer for 78 minutes, the Washington Diplomats squandered a two-goal lead and lost, 3-2, in a NASL shootout at RFK Stadium last night to the Chicago Sting.

"My God, how suffering," Diplomats owner Jimmy Hill said after watching his team blow a 2-0 lead in regulation, then miss some good scoring opportunities in overtime before a crowd of 8,659.

"What a disgrace," Washington Coach Ken Furphy said. "In all my years of coaching I've never had a team do this."

"Agony, man, agony," said Dip goalkeeper Jimmy Brown. "Every week we try and try and try. But nothing comes of it."

The Diplomats took a 1-0 lead at 50:58 on David McGill's fourth goal of the season, off a nice centering pass by Trevor Hebberd.

Washington increased its margin to 2-0, at 66:37, when striker Ross Jenkins dribbled through two Chicago defenders and slid a pass to an unmarked Clive Haywood, who scored his first goal of the season past Chicago goalkeeper Paul Coffee.

Then, in the 70th minute, McGill, who has been suffering all week from a pulled leg muscle, had to leave the game for Ivan Belfiore. Bringing on the defensive-minded Belfiore for the last 20 minutes seemed to be a plus with a two-goal lead. But Belfiore got crossed up on a defensive assignment and Chicago scored.

Belfiore allowed Chicago midfielder Ingo Peter to get free 16 yards to goalkeeper Brown's right for an easy left-footed shot that cut the Dips' lead to 2-1, at 77:04.

Less than seven minutes later, Peter took a pass from the right side and struck the ball cleanly from about 30 yards. The ball sailed over everyone's head, including Brown's, and dipped under the crossbar to tie the score, 2-2, at 81:57.

Then came the overtime.

First, Hebberd and Jenkins worked themselves into a two-on-one situation that should have produced a goal. But Jenkins, who had blown at least four scoring opportunities earlier, pushed a shot that was too soft.

After Brown saved the game for the Dips with a stunning save on Arno Steffenhagen, the Dips had another chance. On a long ball played from Midfield, Haywood hit a magnificient running header, but Coffee was perfectly positioned to stop the shot with his chest.

Chicago had its chances, too. Former Express player Pato Margetic blew a close-in whot with 31 seconds left that would have beaten his old teammates. And Waldron, who defended Chicago's Karl-Heinz Granitza very well, kicked a Peter shot off the goal line after Brown had been beaten. v

Then, ona final attempt, with five seconds remaining before the shootout, Peter Baralic's shot fromthe middle of the penalty area glanced off Coffee but hit the past.

The abbreviated shootout, which Chicago won easily, 3-90, was anticlimactic. One could sense the Dips' were zapped of energy after the overtime. Chicago's Dave Huson scored past Brown in the first round, followed by Derek Spalding and Pato Margetic goals in the next two.

Washington's David Bradford, Malcolm ywaldron and Trevor Franklin were all stopped easily by Coffee, and the Diplomats dropped to 13-15. Nine points behind second-place Montreal with four games left, they are faced with a must-win situation Sunday when Atlanta visits.