The Washington Capitals concluded the celebration of their stunning victory in Boston today and used a brief skate at Nassau Coliseum to prepare for their longest day of the season.

The Capitals play the New York Islanders here Saturday (WDCA-TV 20 at 5 p.m.), then race for a 9:15 flight out of Kennedy Airport, all the while wondering about the Toronto Maple Leafs' progress against the Quebec Nordiques in an 8 p.m. game in Toronto.

"The Leafs have an edge, knowing what we've done and knowing what they have to do," said Washington Coach Gary Green. "If we lose and they win, it's all over. Naturally, we don't expect that kind of result."

The Capitals and Leafs, following Washington's first victory in Boston Thursday, are tied for the 16th and final playoff spot with 68 points each. The Leafs, however, have 27 victories to the Capitals' 25, so Washington must earn one more point than Toronto in the final two games to qualify for postseason play.

The Capitals conclude the regular season Sunday with a 7 p.m. Capital Centre game against Detroit. The finale also will be telecast by Channel 20, if the game is still significant and if it is sold out. A few tickets were still available today. Toronto closes Sunday night with a return match at Quebec, which had a 11-game unbeaten streak before tumbling in Hartford Wednesday.

While Toronto is the obvious target for the Capitals, they can still conceivably overtake Pittsburgh. However, the Capitals have fewer victories, so they would need some far-reaching results to accomplish the leapfrog act.

Pittsburgh, with 71 points, needs only one point in its last two games, against Boston Saturday and Hartford Sunday, to wrap up a playoff spot.

The New York Rangers clinched a berth with a 3-1 victory over Chicago tonight, giving them 72 points, and Edmonton clinched a spot, also with 72 points, when it defeated Vancouver, 7-2.

The Capitals need a little luck against the Islanders, who have beaten them in all three meetings this season, including a 5-4 decision at Capital Centre on Sunday. Washington never has won at Nassau Coliseum and the Islanders are aiming to win their last two games in order to finish No. 1 overall, an achievement that would be worth $5,000 a man.

It is questionable, though, how much No. 1 status and the cash mean to a team that won the Stanley Cup a year ago and has a bulging payroll. The Islanders played the Rangers here Thursday and, despite winning, 2-1, appeared unmotivated.

The Islanders managed only two shots in the first period and in the last minute, after the Rangers lifted their goalie for a sixth skater, the Islanders' Bryan Trottier lost five straight faceoffs to the Rangers' Ron Duguay. During the contest, Islander left wing John Tonelli was forced out with a sprained ankle.

The Capitals gained a huge amount of self-confidence with that 3-2 triumph in Boston, which brought them a club-record third straight road game.

"The last time in Boston we didn't play badly and this time we won," said Bob Kelly, who scored the winning goal with 4:24 left. "There's no reason we can't win tomorrow. It's no different than going into Philly and winning."

Mike Palmateer, who blocked 35 shots in Boston, will be in goal Saturday and Gary Green indicated he would probably play again with veteran defenseman Rich Smith, a standout in Boston, rather than rookie Jim McTaggart.

Both Green and General Manager Max McNab praised the work of defenseman Paul MacKinnon, playing his first full game after returning from a Nov. 1 knee operation. MacKinnon started Sunday, but was ejected in the first period for intervening in a fight between Palmateer and the Islanders' Garry Howatt.

"Mac was unbelievable," Green said. "I know now what I was missing so much of the season."

"The big thing about that game was Paul," McNab said. "It had to mean 13 or 14 points to us to lose him. He is in a class by himself lobbing the puck over the other team to get us out of trouble.