Portland's Stuart Lee, a late substitute who came on at 83:33, fired a loose ball past Washington goalkeeper Jim Brown with 14 seconds left in regulation to pace Portland past the luckless Diplomats, 2-1, in North American Soccer League action tonight.

Lee's entrance provided the Timbers (11-10) with a satisfying end to a wide-open but unproductive game. Portland's final offensive thrust of the geme turned into the game-winner. Diplomat defenders Benny Dargle and Peter Carr both slipped to the Civic Stadium Astro Turf and watched helplessly as Lee fired home from six yards out before a crowd of 8,155.

The Diplomats fell below .500 for the first time since the opening game of the season with a 10-11 record, suffering their eighth loss in the last 10 games.

As both teams professed to play offensive style, the question was which would lull the other's defense to sleep in the first half. Perhaps the Diplomat's most dangerous chance in the opening 35 minutes came 15 seconds into the game when Don Nardiello took a pass following the kickoff and screamed a 15-yard shot that skimmed the right side of the Timber goal.

Washington was the first to awake from an unproductive first half at 39:23, when a Clive Haywood cross found David McGill eight yards in front of Portland goalkeeper Dragon Rodovich. McGill's header beat the former Diplomat goalkeeper for a 1-0 lead.

It was Portland's turn to wake up on offense just 1:20 later. Timber defender Willie Donachie sent a chip shot over the Diplomats' defensive wall on a free kick to find striker Ally Brown on a timely header past the unsuspecting Jim Brown.

The Diplomats got a taste of their own medicine. Ally Brown's goal came on the first successful Timber free kick of the 1981 season, something the Dips and Malcom Waldron have found success with throughout their 20-game season.

The Timber front line continued to pressure Jim Brown with crosses for the remainder of the half. Waldron found little time to leave Ally Brown alone and add to his recent scoring binge.

The Dips added still another variation to their offensive punch. Midfielder David Bradford played like a fourth forward, pushing continuously into the Timbers' 18-yard box before feeding off to Nardiello and Ross Jenkins.

However, Portland's Young Jeung Cho, the NASL's only Korean player, punished the 5-foot-5 Bradford while knocking away a number of Diplomat scoring opportunities. This variation in Washington's offense was not as surprising as the news the Diplomat players received this afternoon. Midfielder Peter Baralic had just been sold to the Tulsa Roughnecks for an undisclosed sum, and Trevor Hebberd was quickly on his way to Portland after being left back home for the two-game road trip.

The Diplomats play in California in a Saturday night match against the Surf.