It has been 40 years since the Stanley Cup rested in a New York trophy case, the possession of the Rangers and such hockey legends as Muzz Patrick; his brother, Lynn; Alfie Pike; Babe Pratt, and Neil Colville.

Barring what, at this stage, would be a miracle, the cup soon will be back, the property of an 8-year-old band of newcomers known as the Islanders, featuring names like Denis Potvin, Bryan Trottier, Mike Bossy, Bob Bourne and Bill Smith.

It may be consigned here as early as Thursday, if the Islanders win game five from the Flyers in the Philadelphia Spectrum. If not, it figures to be anchored down here Saturday afternoon. The Islanders lead this best-of-seven series, 3-1, and both historical precedent and recent performance are solidly on their side.

Only once, in 1942, has a team overcome a 3-1 deficit in the final series to capture the cup. The Toronto Maple Leafs pulled that one off after losing the first three games to Detroit.

The Flyers, injury-riddled and defense-poor, do not seem capable of such a comeback. Coach Pat Quinn thought his club played its best game of the series Monday night, but the Flyers still wound up 5-2 losers, thanks to a lot of mental errors on the back line.

Jim Watson, the Flyers' best defenseman, aggravated a shoulder injury Saturday and is not expected to play again in this series. Bob Dailey, the No. 2 defender, has been playing despite shoulder problems and lacks his usual aggressiveness.

The healthy defensemen have been unable to match their capable play of the regular season, as the Islanders persistently pressure them. Moose Dupont has been pitiful, waving his stick at forwards who duck and race past. Norm Barnes, who replaced Watson, was repeatedly caught up ice Monday and was victimized on all three of the Islanders' third-period goals. Mike Busniuk has been outmuscled and Behn Wilson and Jack McIlhargey appear bewildered by the whole thing.

Despite their obvious failings, the Flyers were not giving up, at least verbally. And the Islanders were taking care not to claim a victory that is not yet official.

"We always tend to make things difficult, so we'll just have to put our backs to the wall and win the next three games," said Flyer Captain Mel Bridgman. "The home-ice advantage seems to be an advantage and after we lost the first game at home, we knew we'd have to win one game in Long Island. It'll just have to be the sixth game."

"The last time I looked, it still took four games to win it," Quinn said. "We'll be ready emotionally Thursday. The trick is to control the emotion so you can execute. If I have any difficulty getting them up for the next game, I guess we should be investigated."

For the Islanders, capturing the cup will accomplish something even more important. It will forever remove from their uniforms that awful "choke" label of past years.

"Let me ask you a question," said Bourne, a leading candidate for the Conn Smythe Trophy as playoff MVP. "Everything we've heard about ourselves . . . how many years could you take it? I still feel the same now as I did after was won the first game. It isn't over."

"We're closer than we've ever been to the cup," Potvin said. "The first thing all of us have to realize is that we still have to win one more. You win the series with four victories. We've got three now. All the marbles are going to be on the next game."

"The two wins here were the big ones," Trottier said. "We won one in there; that's what we wanted to do, and we wanted a sweep here. We're achieving what we want to achieve."

"It takes four games to win the series and the game we have to win is the fourth one," said Coach Al Arbour. "Certainly, it's very nice winning now, but we still have a long way to go. We just play one game at a time and the next one is the one we're after."

Smith, the goalie in all 14 Islander playoff victories, has established a Stanley Cup record. No other goaltender ever won more than 12 in one year. Trottier, with 26 points, is just one away from the playoff record shared by Phil Esposito and Frank Mahovlich.

The Islanders, whose seven shorthanded goals established a Stanley Cup mark, have tied the power-play standard as well. Montreal set that record of 21 in 1965.