The Washington Diplomats, having already secured a playoff spot, resume their battle for a first-round home-field advantage tonight when they host the New England Tea Men in an 8 p.m. North American Soccer League contest at RFK Stadium.

Firmly entrenched in second place in the National Conference East Division with a 17-point lead over Toronto, the Diplomats are now casting eyes toward the West Division. The second place Portland Timbers had a lead of five points over Washington going into the West Coast game against Dallas last night. The team finishes with the best second-place point total in the conference will host a first-round playoff game on Aug. 8 or 9.

Portland has two games left, compared to three for Washington after tonight's game. The Timbers will have road games at doormats Seattle and Colorado; Washington has road contests in Rochester and Toronto, and a tests in Rochester and Toronto, and a home game next Wednesday against the mighty Cosmos.

The diplomats, however, cannot look past tonight's game against the leaders of the American Conference's East Division. Although the Tea Men (16-10) have lost their three games after being struck with injuries to a trio of key players, they still possess a one-man scoring machine in striker Mike Flanagan.

Flanagan has set the league on fire in his initial year of NASL play after being obtained on loan from England's Second Division Chariton Athletic.

He is tied with the Cosmos' Giorgio Chinaglia for the league lead in goals with 29, one short of the season record. Flanagan, 25, tied another league standard when he exploded for five goals in a game against California on July 9. He has nine game-winning tallies in his season, including the goal in a 1-10 victory over the Cosmos, and a goal and an assist when the Tea Men ended the Cosmos 23-game home winning streak July 12.

"You just look for chances," commented Flanagan when asked about his scoring prowess. "I just hang around the net and take them when I can." Flanagan said that he kicks with either food and favors corner-kick situations where he "gets in the goal-keeper's face."

Diplomat defensemn Jim Steele, successful in holding Flanagan score-legs in a 2-1 Washington victory earlier in the season in Foxboro, Mass., missed yesterday's practice with a stomach disorder but is expected to play. Not so fortunate may be left wing Ken Mokgojoa, who reaggravated an ankle sprain in Saturday night's victory and is doubtful for tonight. Should Mokgojoa not play, Mike Bakic would replace him.

Diplomat striker Paul Cannell has another type of problem. Having already accumulated 33 penaly points, Cannell will be forced to miss two games if he gets two more demerits.

Defender Mike Dillon must sit out the Cosmos game because he surpassed the 20-point limit in Saturday's fight-filled Rochester game, where he was one of three players ejected.