The New York Islanders were greeted by an eight-minute standing ovation tonight in Nassau Coliseum. Then they provided their fans with reason to yell even louder by defeating the Montreal Canadiens, 5-3.

"Help us win the Cup" was the message spread by handbills distributed before the game, urging spectators to surpass the 7 1/2-minute noise salute Los Angeles fans lavished on the Kings two weeks ago. The fans complied and, if the Islanders are still a tall drink away from the Stanley Cup, at least they know the Canadiens are human.

Montreal had won 11 straight playoff games, matching a Stanley Cup record, since losing here in the fourth game of the 1976 semifinals. Thus, they are ahead of schedule, trailing 2-1 in the best-of-seven series that continues here Saturday night.

The Islanders' heroes were many. Goalie Billy Smith stopped 35 Montreal shots, including 16 in the final period. Jude Drouin's sharp passes set up three goals, including two by Denis Potvin. Ed Westfall won eight of nine faceoffs in the final period, all four after Montreal lifted goalie Ken Dryden for a sixth skater with 1:19 remaining.

Westfall outdrew Jacques Lemaire in Islander ice and flipped the puck to Bryan Trottier, whose 120-foot shot with 11 seconds remaining provided relief for the frazzled nerves of home fans.

New York, which broke a 2-2 tie on J. P. Parise's goal at 6:04 of the second period, seemed destined for success when Andre St. Laurent made it 4-2 with 8:51 left in the game.

The Canadiens, unaccustomed to losing (this was their second setback in 41 games), injected a little apprehension into the 15,317 fans with Guy Lapointe's second goal of the game as 3:40 was left on the clock, Lapointe, in the right-wing circle, took Lemaire's cross-ice pass and drove it off the arm of Smith, who dove from right to left to try to cover up.

Before Trottier settled it, Smith blocked a difficult Doug Risenbrough rebound of a Serge Savard drive, then turned back a Guy Lafleur blast followed by a 40-foot Lemaire rebound.

Smith, brother of Washington defenseman Gord Smith, has played all nine playoff games while Chico Resch, one of the league's fine goaltenders, plays the role of cheerleader.

"This is the bggest surprise to the hockey world," Smith said, "Me playing instead of Chico. He had the better season, but at the end I had one hot game and (coach) Al (Arbour) went with me instead of Chico. I'm fortunate to be in there.

"I'd be tired normally, playing nine in a row. But Al is treating me with care. I don't do any hard skating at practice, nothing to fatigue myself. I just take a few shots to keep my reflexes sharp. That's all it is when you play so much - reflexes."

Smith credited the crowd's support for giving the team a lift - "That's the loudest they've been in the five years we've been here. They got us up for a good start." But it was obvious Smith was already psyched up. As he skated out for the warmup, a fan patted his back and he turned, stick up, ready for combat.

"It feels good to beat them once," Smith said. "But we have to beat them three more times."

"You can't win them all," said Montreal coach Scotty Bowman, who added, "I hope we don't lose them all."