The Washington Capitals played their best game of 1981 tonight. The result was the same as the other four, however, as a spectacular third-period goal by Al MacAdam carried the Minnesota North Stars to a 3-2 victory.

Washington was involved in a line change when MacAdam battered the puck away from Mike Gartner at the red line. As MacAdam pursued the puck into Washington ice, Ryan Walter came off the Capitals' bench and became entangled with defenseman Rick Green, who was turning to go after MacAdam.

The two Capitals fell, leaving MacAdam a clear breakaway, and he drilled the puck through goalie Dave Parro with 10:57 left for the decisive score.

There were more thrills for the 15,399 fans before the contest ended, but there was no further scoring. Minnesota's Gilles Meloche, who shut out Washington here a week ago, made a big save on Glen Currie with 6:09 left and then turned aside a drive by Pat Ribble in the closing seconds after Parro had been lifted for a sixth skater.

Parro made 38 saves as Minnesota outshot the Capitals, 41-29, and he was especially brilliant during the first 6 1/2 minutes of the second period, when the North Stars fired 11 unanswered shots at him.

The Capitals were obviously buoyed by Parro's fine play and the return of defensemen Pat Ribble and Rick Smith. Although they suffered a fifth straight defeat for the second time this reason, there was reason to believe the Capitlas at least are competitive once again, following four straight shellackings.

"I thought we deserved at least one point tonight," said Coach Gary Green. "We got a few guys back and I thought we made a hell of a start for a comeback. If we play that well, we'll beat all the teams below us nine out of 10 times.

"The guys played a disciplined, hard-working game. I just hope it doesn't get them down, coming out of here without anything. Points are the reward, but the important thing is for the guys to realize they played a solid game."

The Capitals scored first, Jean Pronovost sliding a backhander past Meloche's pad just inside the post for the first goal by a member of the Roaring Twenties Line in five games.

Minnesota retaliated on two power-play scores by Steve Payne and Steve Christoff, making an extra-man yield of six against Washington in the last two games.

Then there was a milestone for the Capitals. With Minnesota's Tim Young off for holding, Mike Gartner sent a shot between the legs of Meloche, who was screened by Dennis Maruk. It was the first power-play goal of 1981 for the Capitals, their first success in the last 36 opportunities.

MacAdam then ruined the night for the Capitals, who have won here only once in seven seasons.

Ribble played an outstanding game in his first competition since he suffered strained ligaments in his right knee Dec. 20. On one occasion in the third period, when Parro went after a puck in the corner and was trapped, Ribble filled the vacated net and blocked a drive by Craig Hartsburg.