With field general Jim Steele in the locker room nursing a possible broken jaw and goalkeeper Bill Irwin playing the final 24 minutes on one leg, the Diplomats turned to a mugging defense to stymie the Dallas Tornado, 2-1, in a foul-plagued, physical North American Soccer League contest before 8,371 at RFK Stadium yesterday.

Joe Mallett, the Diplomats' assistant coach, handled the team in place of injured Coach Gordon Bradley. Mallett looked like a genius when he inserted speedburner Ken Mokgojoa just past the midway point of the second half to give a spark to the home team's offense.

The South African winger, a master of one-on-one moves, hammered in his only attempt of the afternoon from 16 yards out with just 3:11 to play, breaking a 1-1 tie and giving the Dips their fifth win in seven games.

The eight-point pickup kept the Diplomats in second place in the National Conference Eastern Division with 44 points, but Washington lost ground to the division-leading Cosmos, whose 3-0 victory over Houston raised their point total to 59.

Mokgojoa's goal was his second of the season. "When I hit it I knew it was good," he said. "I had a problem getting into the flow when I went in (with 24:35 to play) and I missed on a few passes. I guess this sort of makes up for the Rochester game."

Mokgojoa was the goat in Washington's 1-0 loss to the Lancers two weeks ago when he inadvertently failed to clear out a ball and Rochester scored.

Irwin, who had the best goals-against average (0.80) in the National Conference and the second best in the NASL, was injured in a collision with teammate Tommy O'Hara and Jimmy Ryan of Dallas.

The three players came together while leaping after a crossing pass and they lay on the field for several minutes. O'Hara and Ryan had the wind knocked out of them but Irwin suffered a pulled hamstring in his right leg.

"I got caught in the air," said Irwin, who again had a fine game, although credited with only one save. "I heard it pop when I came down. I hope not to miss any games."

Irwin had to remain in the game because Mallett had made his maximum three substitutions. He replaced Steele with Rene Breevoort at the start of the second half and Sakib Viteskic joined Mokgojoa in place of Sonny Askew and Bobby Stokes.

Viteskic, who had missed the last game with a leg injury, was miffed when he did not start. He refused to talk much about Mallett's decision to use him as a substitute, saying only, "It's his (Mallett's) job to coach and my job to play."

Irwin was virtually helpless after his injury, but the Dips used every trick in the trade, with the exception of outright assault, to keep the aggressive Tornado at bay.

The Diplomat's tight zone defense completely throttled wingers Zequinha, Willi Lippens and Milton in the final 20 minutes.Dallas managed only three shots in the second half, only one while Irwin was limping between the posts.

"That's what upsets me," steamed Dallas Coach Al Miller. "They have a one-legged goalie and we get one shot. We think slowly or something. We didn't take any shots, make any crosses, never tested him.

"We got the equalizer and then let down. It's a bad mistake not to put any pressure on him at all. It's a terrible way to lose."

Dallas, trailing, 1-0, tied the game on a Milton goal at the 63:45 mark. The Brazilian caught up with a nice pass from Ryan, and, despite being sandwiched by Diplomat defenders Don Droege and Mike Dillon, lofted a soft ball over Irwin's head for the goal.

That was it for the Tornado, who have lost three straight to fall to 3-4. When Irwin got hurt, the Washington defense began to play a physical brand of soccer that would have made any NFL coach proud.

"Dallas played the most physical game I've been in for awhile," O'Hara said. "The game got out of hand. But you can't let any team intimidate you. We have big boys who dish it out, too. We couldn't let them come in here and dominate us."

Except for a few vicious tackles and some pushing and shoving, the first 25 minutes of the game were uneventful.Washington had two scoring opportunities, but missed them both.

Paul Cannell put the Dips on the board with a five-yard left-footed boot under the dives of Pedro Gano and goalie Alex Stepney. Steele's soft crossing pass was handled by Alan Green, who slipped the ball to Cannell for the goal at 28:30.

Six minutes later, Steele got into a bumping match with Tornado left back George Ley on the sideline. Steele appeared to elbow Ley first. Ley retaliated with an elbow that caught Steele flush on the jaw. Both players were assessed yellow cards (cautions).

"I didn't elbow him; I had my hands out high and he turned and hit me," said Steele, who left immediately after the game to be X-rayed. CAPTION: Picture 1, Dallas goalie Alex Stepney makes a save on a near point-blank shot by Diplomat Sonny Askew. By Gerald Martineau-The Washington Post; Picture 2, Joe Horvath, left, of the Diplomats collides with Dallas goalie Alex Stepney, right, as defender Pedro Gano moves away from play By Gerald Martineau-The Washington Post