For the fourth straight spring, it rained champagne on Long Island.

By defeating the Edmonton Oilers, 4-2, tonight, the New York Islanders fulfilled the promise of their year-long slogan, "Bring Fourth the Cup," and became the first postexpansion team to win four consecutive Stanley Cup championships.

"It takes everybody on the ice to make a winner," said Mike Bossy, who scored the winning goal--the first player to score cup-winning goals in successive years--and had five game-winning goals in the playoffs, a National Hockey League record. "We concentrated and did what we set out to do."

What they set out to do was win the cup, and what they did was sweep the Oilers, four games to none--just as they had swept the Vancouver Canucks a year ago.

"We had the guts to ignore everything that was said and written about us and just concentrate on what we were here for," said goalie Billy Smith, who won the Conn Smythe Trophy as the most valuable player in the playoffs. His spectacular play kept the Oilers' Wayne Gretzky from scoring a goal in the four games.

Al Arbour, a winner of three Stanley Cups as a player and now four as a coach, called this victory "the sweetest of them all. There is no team with greater character in any sport."

For a brief time, it seemed the Islanders might have to scramble aboard an Alberta-bound plane for a fifth game. Their three goals within a two-minute span of the first period established what they hoped was an undisputed advantage. The Oilers crept closer with goals in the first and last moments of the middle period, but that was as far as they could go.

Ken Morrow's empty-net goal with 1 minute 9 seconds left provided all the insurance New York could want.

"We knew it wouldn't be easy," said Bryan Trottier, who opened the scoring on a power play. "But we got a lot of great efforts out there."

Trottier scored when Clark Gillies sent him a cross-ice pass, which Trottier scooped up near the faceoff circle and lifted behind Andy Moog at 11:02.

Forty-three seconds later, Bob Nystrom chased the puck into the corner and flipped it out toward the front of the Edmonton net, where John Tonelli's stick sent it upward over Moog's outstretched leg.

Bossy's goal was the classic rush hockey fans love to watch. Taking a long pass from Trottier just over the red line, he picked up speed and skated straight for Moog, waiting until the goaltender had moved out of his net before flicking the puck squarely into the back of the cage. Bossy led all playoff scorers with 17 goals as the Islanders extended their victory streak to 16 in the series.

But Edmonton had hardly quit. "This is a team that never quits," said Moog. "And we are a much better hockey club than a four-game sweep."

Gretzky set up the Oilers' first goal, swinging the puck to Jari Kurri near the faceoff circle in front of Smith. Kurri's shot went high and Smith whirled to see the red light flash behind him.

Then Mark Messier controlled a pass from Lee Fogolin, knocked over Anders Kallur and sent the puck sailing over Smith's left shoulder.

"There wasn't any doubt (about winning), even after they got the two goals," said Nystrom. "We never stopped feeling confident."

The Oilers tried to display a similar confidence during the third period, but couldn't generate enough of an attack to make any difference.

But one attack did make some difference, at least to the individuals involved. Glenn Anderson, standing in the slot area, turned and whacked Smith on the side of the head at 8:26 of the third period. Smith immediately fell to the ice, and Anderson was given a five-minute slashing penalty.

"I was hurt about as bad as Gretzky was in the second game," Smith said, referring to last week's incident in which he hit the center. "Anderson rapped me across the throat with his stick and got most of my mask. When Gretzky got hit, he cried and went down, so that's what I did. I got on my back and squirmed, and they got the five-minute penalty. Two can play at that game."

Smith sounded angry when discussing that situation, which overshadowed his skillful play during the early part of the series. "You better believe I'm bitter," he said. "You reporters blew it all out of perspective. This was the toughest series, because of all that aggravation. It made things mentally strenuous."

For Gretzky, the series had to be equally strenuous. He had not scored a goal in five games--four against the Islanders, one against Chicago--and finished with just three assists in four games.

"It wasn't one person," he said. "As a team, they played disciplined hockey and, without a doubt, they shut us down offensively. When we did break them down, Smith was always there with the big save. And their patience and composure were a lot better than ours. That might have been the difference in this series."

He added: "I don't think we were clobbered. We fought hard and we'll be back next year. I don't think it hurt us."

The Islanders became only the third team and the second franchise to win more than three consecutive Stanley Cups. The 1956-60 Montreal Canadiens hold the record with five while the Canadiens of 1976-79 won four just before the start of New York's reign.

The Islanders came into existence in 1972 and made the playoffs in their third season, 1974-75, and have not missed making the playoffs since. They remain the only team in this decade to hold the Stanley Cup.

The Islanders finished second in the Patrick Division this season with a 42-26-12 record.