"I wish you weren't coming to this game," said the woman in the New York Islander's office. It was nothing personal. Saturday night, the Islanders must play the Buffalo Sabres here in a contest nobody associated with the New York club -- and few others -- expected to be necessary.

A week ago, the Islanders ran the Sabres out of Nassau Coliseum, 7-4, to take a 3-0 lead in the best-of-seven Stanley Cup semifinal. Everyone, from television commentator Gerry Pinder to the Islanders themselves, considered triumph No. 4 a mere foramlity and there was more talk here about Philadelphia than Buffalo.

Yet the Sabres are back again, for game six (WBFF-TV-45, 8 P.M.) and suddenly there is reason for the Islanders to worry. Certainly, they know if any team does, that a 3-0 lead is not certain victory, for in 1975 the Islanders became one of two NHL teams to wipe out such a deficit, shocking Pittsburgh in the quarterfinals.

More important than historical precedent is the way the Sabres beat the Islanders Thursday in Buffalo. It was by a 2-0 score, with goalie Bob Sauve recording the shutout and the Sabres controlling play between the blue lines in the manner that enabled them to win the Vezina Trophy for least goals allowed during the regular season.

"That's the pattern we used during the regular season," Sauve said. 'This teams has a lot of natural goal scorers. All we have to do is play tight defense and wait for the break."

The breaks Thursday came on power plays, with John Van Boxmeer and Richie Dunn connecting. That was more good news for the Sabres, since they had failed to take advantage of the Islander's penalty proclivity earlier in the series.

"Our power play is starting to sing again," said defenseman Jim Schoenfled. "If they're going to hit us tomorrow night, they're going to have to be careful."

Much of hockey is mental and it is interesting to gauge the psychological impact at this stage of the series. The Sabres, given up for dead, possess that momentum" that analysts never cease to extol. The Islanders, semifinal losers four times in the last five years, could be excused for wondering whether the finals will somehow elude them once more.

"They have to be starting to think about the past," said Buffalo captain Danny Gare. "They've got to be thinking a lot. I know the feeling when we couldn't get anything past Billy Smith. It feels like there's a brick wall there. But everything we've done all year is coming back now."

Conversely, Islander goalie Chico Resch, who replaced Smith Thursday, figures the pressure will be on the Sabres, who are still just one defeat from oblivion.

"The heat's on them, because they've got something to lose now," Resch said. "When you're down 3-0, it's easy to play, because you've got nothing to lose. Now they'll start worrying. 'We gotta win this one.'

"As for us, we have to concentrate a little more. When you're up 3-0, you're happy-go-lucky. You take things for granted. Now we have to bear down again."

No doubt the Flyers, already qualified for the finals, will be watching this one on their television sets, but they have expressed little preference for an opponent. The way they ran the Minnesota North Stars out in four straight after losing the opener, the Flyers must be considered favorites over either team.

"Philly's got the team to beat," said Minnesota defenseman Craig Hartsburg. "You've got to give them all the credit. They were just better than us. They've got balance. Every guy on that team does the same thing. He works. The key to winning is having 20 guys doing the same thing."

"I think right now that we might be playing our best hockey of the year," said Flyer Coach Pat Quinn.

Considering the incredible 35-game unbeaten streak during the first half of the regular season, that was quiet a statement. But nobody who watched the Flyers against the North Stars was disputing it.