Seattle may be just the opponent the Washington Diplomats need to increase their confidence.

The Sounders, who will play the Dips in RFK Stadium today at 5 p.m., have scored more goals, 47, than any other team in the NASL except the Cosmos. But their defense has allowed 39 goals, nearly two a game. And that is good news for the Dips, whose forwards haven't scored in nearly three weeks.

Washington won its last game, beating San Diego, 3-2, in a shootout Wednesday, but needed a lucky shot from defender Peter Carr and excellent goalkeeping by Jim Brown to do it. The Diplomat defense has played well the last month although the team has lost six of its last seven games.

Seattle, albeit offensively potent, doesn't possess nearly as many weapons as the Cosmos or the Chicago Sting, whom the Dips have contained this season. In addition, striker Roger Davies, the league's most valuable player in 1980, has been inconsistent and playmaking midfielder Alan Hudson missed Seattle's last game with an injured ankle.

The Sounders often attack with five and six men, which makes them popular to watch but easy to counterattack. The Dips, although remarkably inaccurate lately, should be able to take more shots at Seattle goalkeeper Jack Brand.

Coach Ken Furphy has said his Dips will try to improve their offense by using four forwards. Don Dardiello, who played well in his first start of the season Wednesday, may start again. Johan Cruyff, still hampered by recent groin surgery, will not start, but will be in uniform.

Paul Cannell, who did not dress for Wednesday's game, may replace striker Ross Jenkins, who has had trouble scoring. Still, with only 13 games left this season, Furphy continues to search for a front line that can score consistently.

The Dips, who after this evening play their next two games away from RFK, are nine points ahead of Montreal in the race for second place in the Eastern Division. The game against Seattle is being started at 5 o'clock so that those watching will be able to attend the July 4 fireworks display later tonight.