The Washington Diplomats, taking advantage of numerous Dallas Tornado mistakes, rode two second-half goals by Alan Green to a 4-2 victory at RFK Stadium yesterday.

The Dips, before a crowd of 15,273, evened their North American Soccer League record at 2-2 and earned nine points for a season total of 21. This was Dallas' first defeat in four games.

For the first 70 minutes, the Dips had things all their way. They had a 2-0 lead at the half, thanks in part to some mental breakdown by the Tornado defense, and grabbed what appeared to be an insurmountable 3-0 lead following Green's goal at 55:24.

"The game should have been over," said Dip defender Carmine Marcantonio, who scored Washington's first goal.

"We were ahead, 3-0, and should have just tried to retain possession of the ball. But we were throwing people up front trying to score more goals. When Dallas got the ball, the defense didn't have much help and that's how they scored."

Washington was guilty of relaxing a bit on both Tornado goals.

Zequinha, relatively quiet much of the game, got just enough space to get off a shot and his 15-yard squibber slid under diving Dip goalie Bill Irwin at 70:59.

Minutes later, Dallas was on the attack again. Tony Bellinger, who had the monumental, day-long task of keeping Dip leader Johan Cryuff under wraps, gained contol of a loose ball that Washington defenders failed to clear out of the box and rifled home a shot that also eluded Irwin.

"That was a terrible goal," said a miffled Irwin, who until the quick one-two had been outstanding. "The first one, I just had the wrong angle. The second one, I should have had. On 99 out of 100 tries, I would have come up with it."

But this was the one in 100, and with less than 10 minutes left, Dallas had a golden opportunity to tie the game. Stiker Klaus Toppmoeller played Zequinha's corner kick perfectly but his header banged off the top of the crossbar. The ball bounded to Dallas' Omar Gomez, but his volley attempt also hit the top of the bar.

"We make that shot, it would have been Katy, bar the door," remarked Bellinger. "It was a matter of inches. The second half we had our chances."

Washington was not about to give the Tornado yet another opportunity. Playing the fierce, aggressive defense that limited Dallas to six shots in the first half, the Diplomats shut down the Tornado attack.

Green then put Dallas' rally to rest by hitting a 15-yard floater on which Tornado goalie Billy Phillips had no chance. The goal, Green's fourth of the season, came following a give-and-go pass from Wim Jansen at 82:43 of the 90-minute contest.

Phillips, a rookie from Adelphi-College, had given up only one goal before yesterday. Washington managed only one more shot than Dallas (18-17) but gave the 23-year-old goalie a rough afternoon.

"We wanted to put pressure on the young American keeper," Washington Coach Gordon Bradley commented. "We didn't think he had been tested in his first three games so we came out pressing. He made a couple of mistakes and we took advantage of them."

The first mistake could not be totally blamed on Phillips. The teams were locked in a defensive battle before Marcantonio dribbled past several napping Tornado defenders and drilled a 22-yard shot inside the right corner of the net to give the Dips the lead at 34:06.

"I had two or three good chances already but this one I hit," said Marcantonio, a converted midfielder. ""I shoot a lot because I usually go up on all the set plays. This one wasn't, though."

Since the Diplomats had missed several chances to score, Dallas seemed lucky to be behind by only 1-0. But with the clock tickling down the final minutes of the first half, disaster in the form of Joe Horvath struck the Tornado.

The left-footed midfielder, who played such a brilliant game in Washington's 3-1 defeat of Philadelphia last week, took a pass on the left side of the box from Bobby Stokes and was looking for someone to break free across the middle.

The Dallas defenders did not bother to challenge Horvath and the Washington players, probably sensing something good was about to happen, didn't come into the box. So Horvath sent a high, twisting ball toward Phillips. The kick kept rising and curving, and Phillips' desperation leap was not close as the ball found the back of the net. Washington led, 2-0, with 1:02 to intermission.

"It was luck," said Horvath, who left the field late in the second half with a bruised foot. "I was trying to shoot it in the middle to either Alan or Bobby. I was surprised the ball went in."

Dallas still had not recovered from the Horvath goal when the same midfielder, after taking a pass from Cruyff, shoveled the ball to Green, who streaked past defender Gert Trinklein. Green easily controlled the ball and rolled a five-foot shot past Phillips to give the Dips a 3-0 lead.

"Joe knew where I was and I got to the ball before the defender." Green said. "The goalie made a mistake on the goal. The second one bent a bit when I stoked it."

Green's second goal "was a relief," sid Coach Bradley. "We let down and they came back. Sonny (Askew), Joe and Nick (Mijanovic) all played great games (for Washington). We regrouped at the end when we had to. But we needed that last goal to put them away."