hey displayed replicas of 2 1/2 Stanley Cups on the Nassau Coliseum message board tonight and the crowd of 15,230 responded enthusiastically. The New York Islanders responded, too, coming closer to winning Cup No. 3 with a 5-2 victory over the Quebec Nordiques.

Mike Bossy scored twice and goaltender Bill Smith survived a 30-shot barrage by Quebec in the first two periods as the Islanders took a 2-0 lead in the best-of-seven series leading to the Prince of Wales Conference championship. Game 3 will be played Saturday in Quebec City, where the Nordiques are hoping their rabid fans will help turn the tide.

"Our crowd is like a seventh player on the ice; they're really happy in Quebec to see us in there," said Coach Michel Bergeron. "I'm still confident. I know we're playing a great hockey team and we are very young. They take advantage of our mistakes; we have to do the same."

Most of the Islanders' errors, few as they were, resulted in nothing more than saves by Smith. He blocked 16 shots in the second period, when the Nordiques pulled into a 2-2 tie and had some good chances to take the lead.

It was even when Smith stopped Anton Stastny, on a setup by brother Peter, after the Islanders' Gord Lane was unable to stop the puck at the blueline. Quebec's Dave Pichette then hauled down Bob Bourne on a breakaway and the Islander power play, best in the NHL during the regular season, was able to break the tie.

Bossy, fed by Denis Potvin, scored from the same spot at the inner edge of the left-wing circle that he had connected from earlier in the period. The first shot sailed over the left shoulder of goalie Dan Bouchard; this one slipped between Bouchard's legs.

"The other night I had two good shots from the slot and they hit him (Bouchard)," Bossy said. "Tonight they went in. They opened it up in the second period and for some people I guess that gave the series some excitement. Both goalies were making great saves and it was up and down. We can play that way, but we're more effective when we just grind it out."

In the third period, the Islanders reverted to form and smothered the visitors. The spirit seemed to disappear from the Nordiques at 3:46, when a seemingly routine 30-foot shot by Bourne struck Bouchard's right pad and popped into the net for a 4-2 margin.

Bob Nystrom's rebound of a Bourne shot, with the Nordiques unable to clear the front of the net, completed the scoring and sent the Islanders out of town with a record of losing only two of their last 31 home games.

"The second period I thought we were playing on Lake Superior," said Coach Al Arbour. "When I was a kid, we did that. We'd go to their end and test their goaltender and they'd come to our end and test our goaltender. It was wide open, but Bill Smith came through for us and made a lot of big saves.

"The third period was more our game. We've got to be more consistent. We're playing 20 minutes, 30 minutes. We have to play 60 minutes. They're a dangerous hockey club."

The Islanders scored first, for the 11th time in 13 playoff games, as Bouchard took a belly flop at a puck that seemed headed for an icing call. He deflected it, but lost his stick and, after Quebec's Wally Weir and the Islanders' Anders Kallur slid past, Wayne Merrick came in as a trailer and easily lifted the puck into the empty net.

Marc Tardif matched that goal for Quebec, beating Smith on a short-side shot that struck the goalie's left pad and popped high into the net.

After Bossy converted Bourne's pass from behind the goal line, Peter Stastny pulled the Nordiques even a second time by faking both defenseman Gord Lane and Smith and depositing the puck in the net.

It was the last time Smith needed to turn around.

Black Hawks 4, Canucks 1: In Chicago, Denis Savard scored two third-period goals--his ninth and 10th of the playoffs--to even the Stanley Cup series with Vancouver at one game apiece.

Glen Sharpley added a goal and an assist in the game, which was disrupted by several fights. Officials called 188 minutes of penalties, 150 in the final period.

Vancouver was assessed a bench penalty after Savard's second goal when players waved white towels at the officials and Coach Roger Neilson left the ice.

The third game of the best-of-seven Campbell Conference championship will be played Saturday in Vancouver, where Chicago has not won in its last seven appearances.

Savard's goal at 4:42 of the third period gave the Black Hawks breathing room after Vancouver's Stan Smyl cut the lead to 2-1 at 1:01 of the final period. Savard's second goal came on a power play at 16:23.

The loss was only Vancouver's second in its last 19 games. The Canucks had won eight of their first nine Stanley Cup games this year.