Washington's longest-running soap opera -- Days Of Our Diplomats -- produced another depressing episode for the protagonists tonight.

This was a familiar episode, an oftenseen summer rerun. The scene was the road and the result for the Diplomats was another loss, this one 2-0 to the Vancouver Whitecaps in front of 30,131 in Empire Stadium.

The goal that dropped Washington's record back under .500 at 14-15 came 12:33 into the game, when the top Whitecap scorer, Trevor Whymark, beat Dragan Radovich with a right-footed volley into the left corner of the net off passes from Kevin Hector and Bob Lenarduzzi. The insurance goal came from Carl Valentine at 88:48.

The win raised the 1979 Soccer Bowl champions' record to 15-14, good for 128 points and should about wrap up a playoff spot for them.

Even in defeat the Dips moved closer to a playoff spot because Toronto was beaten. With 134 points the Dips need 12 points in their last three games to clinch second place in the NASL National Conference East.

The loss dropped the Dips' road.

After being outplayed the first half, they controlled play the second half and had several excellent scoring chances. But time and again they were stymied by Vancouver goalie Bruce Gobbelaar, the game's top player, who made several superb stops in richly earning his eighth save of the season. It was the fourth time this season the Dips, 0-8 lifetime in games played in Canada, had been shutout.

It was also their second consecutive defeat after a six-game winning streak that had the team believing it finally was on the right track. The club has until next Sunday to regroup before traveling to New Jersey to face the Cosmos.

That game, like this one, will be on Astro Turf. It may also produce an evening similiar to this one, the type of evening the Dips are accustomed to when playing away from RFK Stadium.

A gorgeous Canadian summer evening and the presence of Johan Cruyff combined to fill ancient Empire Stadium with a raucous, singing crowd well before kickoff.

The charged-up atmosphere had a far more positive effect on the Whitecaps than on the Diplomats. They dominated the flow of the first half. They were so much in control most of the time that they looked like the big kids playing keep away from the little kids in the schoolyard.

It took Vancouver only 30 seconds to get off its first shot and it only 12:33 for the Caps to put the ball in the net.

The goal came on a superb play set up by two of last year's Soccer Bowl heroes, Kevin Hector and Bob Lenarduzzi. Hector dribbled into the left-hand corner, stopped short and lofted a pass into the box to Lenarduzzi, playing up at midfield because of injuries.

Lenarduzzi charged in, but instead of trying to head the ball past goalie Dragon Radovich, he touched the ball off his head to Trevor Whymark, dashing in front the right a step ahead of Nick Mijatovic. Whymark, the leading Whitecap scorer, took the pass on his right foot and swiped it past Radiovich from seven yards, beating the goalie cleanly to his left for the 15th goal.

That put the Dips in a familiar road position: behind. Washington's TV fans, who missed the first 37 minutes because of telephone transmission problems, didn't miss too much from Washington's standpoint offensively.

Never a good Astroturf team, the Diplomats were clearly bothered by the slick surface. Because they did not feel confident with passes on the ground, they tried again and again to loft high passes into the penalty area.

That tactic was completely ineffective as the Vancouver defense and goalie Bruce Gobbelar were in the right place to volley the ball clear or grab it in midair.

Frustrated by their inability to gain control of the ball, the Dips resorted to rough tactics, committing 16 fouls in the first half. Many of the fouls were committed by Washington players who were about to be left behind by Vancouver's small, quick forwards.

The 1-0 halftime score represented a minor victory for Washington since it seemed as if the Whitecaps were almost constantly on the attack the first 45 minutes. Vancouver outshot the Dips, 11-5, in the half. Washington's only legitimate scoring chance came at the 26-minute mark when Tony Crescitelli volleyed a header off the crossbar after Cruyff's corner kick.