Utopia will visit Nassau Coliseum June 7. That is the rock group; the New York Islanders expect to find Utopia of a different variety much earlier.

The Islanders swept past the Philadelphia Flyers, 5-2, tonight and secured a stranglehold on the Stanley Cup. With a 3-1 lead in the best-of-seven final, the Islanders and their fans are preparing a giant celebration when the Cup comes to Long Island for the first time.

The fans, who take delight in drowning out the National Anthem, were chanting "We want the Cup" long after the game ended, prompting Flyer Coach Pat Quinn to note, in an interview room beneath the stands, that "they're really having a great time up there."

Quinn also pointed out that "the last time I looked it still took four games to win it." The Islanders' opportunity to win that fourth comes Thursday night in the Philadelphia Spectrum and there will be two more chances even if the Flyers manage to avoid the steamroller.

"We're not celebrating yet," winger John Tonelli said in the fairly subdued Islander dressing room. "You don't celebrate until you win it all. But we will win it."

The Flyers were in no mood to dispute that or any other point, particularly since "we played out best game of the series," according to Quinn. If the Flyers' best brought a three-goal defeat, there is little reason for optimism.

The big play tonight was made by Islander winger Bob Bourne, with only 7:25 remaining in the game. Just 42 seconds earlier Ken Linseman had converted a Brian Propp pass to lift the Flyers within one goal at 3-2 and hope was stirring on the Flyer bench.

But Bourne blocked Bob Dailey's attempted shot from the right point and scooped up the puck. He and Bob Nystrom broke loose against Flyer defenseman Norm Barnes, who stayed with Nystrom until Bourne was approaching the net. Then Barnes went after Bourne, a big mistake, since Bourne merely slipped the puck to Nystrom for an easy score.

"The big play was Nystrom's goal," Quinn said. "They blocked a shot at our point, which was a miscue, and we wish it hadn't happened, but what do you do? There were a lot of less-than-smart plays by our point men. They wanted to score and gave it away.In the second period our goaltender (Pete Peeters) saved us, but in the third period he couldn't save us."

Mike Bossy, on the Islanders' first power-play chance, and Butch Goring sent the Islanders in front in the first period, 2-0. Then the Flyers got a lift from a score at 1:35 of the second period by John Paddock, playing right wing in place of injured Paul Holmgren.

Paddock skated down the right side, wound up from the outer edge of the faceoff circle and sent the puck high into the far corner, past startled goalie Bill Smith. It was Paddock's first shot on goal in Stanley Cup play, in only his second game.

"I haven't really played a game in six weeks, except for a few shifts against Edmonton, and the legs aren't there," said Paddock, traded to Philadelphia by the Washington Capitals four years ago for Bob Sirois. "With the steady games, we haven't had any hard practices. I've been riding the bike to keep my wind and the wind is okay, but the legs aren't."

The Flyers had 10 more shots in the second period, but Smith stopped all of them. Meanwhile, Peeters was turning aside breakaways by Bossy, Wayne Merrick and Bourne, all resulting from misplays at the New York blue line and all but Merrick's coming with New York short-handed.

It was still 2-1 at the six-minute mark of the third period. Then Islander Garry Howatt skated down the right side and dropped a pass for Bryan Trottier. Both Mel Bridgeman and Barnes, the replacement for ailing Jim Watson, watched Trottier curiously and, after faking Peeters one way, Trottier unhurriedly drilled the puck into the net.

It was Trottier's 26th playoff point, one short of the record shared by Phil Esposito and Frank Mahovlish. No. 25 was a gift, a second assist on Bossy's goal, on which Clark Gillies took the puck from Flyer Mike Busniuk before feeding Bossy.

Linesman then gave the Flyers life, buy Nystrom took it away and Gillies, with 5:52 left, removed any doubt from the outcome beating the weary Peeters from the right-wing circle.

Despite Paddock's goal, the Flyers obviously missed Holmgren and Watson. Barnes was caught up ice all night and was a victim on all three New York goals in the third period.

"When you miss two of your better players, it takes a toll," Quinn said. "During the season you can win despite injuries if you have more people going than the other side. At this level, though, it's tough."

Islander Coach Al Arbour was not enthused with his team's play, but said, "We didn't play superb by any means, but we hung tough and did what we had to do to win. It was very warm in this building tonight and the ice was like skating on hard snow. It made it tough for both teams."

Right now, though, it could hardly be tougher for the Flyers. Only the 1942 Toronto Maple Leafs, who lost the first three games to Detroit, ever have overcome a 3-1 deficit to win the Cup.