NEW YORK, SEPT. 23 -- After months of ignoring his fitful, hopeless and largely invisible challenge to Gov. Mario M. Cuomo, New Yorkers are finally noticing Pierre A. Rinfret.

But the recognition, coming after the Republican candidate for governor first threatened to withdraw from the race, then publicly denounced the party leaders who nominated him, has Republican officials nervously biting their nails and Democrats biting their lips to keep from laughing.

"Would I rather have had a candidate not fall apart in public?" asked Sen. Guy J. Velella, the Bronx Republican leader and chairman of the State Senate Republican Campaign Committee. "Absolutely. But I am still supporting him. My children have temper tantrums and I still love them. He's got to calm down, but I prefer him to Mario Cuomo."

Even in this year of anger against incumbents and an incipient recession in New York, nobody really doubts that Democrat Cuomo will win reelection. But Rinfret's spectacular attacks on his comrades have made people wonder for the first time if the fairly solid Republican majority in the Senate could be vulnerable in November.

When Rinfret referred to the state's Republican establishment last week as "the Geritol set," pointing out they had "been in office for 20 to 30 years," he opened a wound Democrats here are eager to exploit. The Democrats control the Assembly and the Republicans hold a 32 to 26 edge in the Senate. But officials fear that indifference to Rinfret could so reduce voter turnout that Democrats could sweep in.

Republican officials here are quick to point out that they fared well in state elections even in 1986, when Cuomo was reelected with the largest margin of any governor in the state's history.

"The linkage just isn't there between state Senate seats and the governor's race, though we do need to make sure people go to the polls," said state Sen. Roy M. Goodman, the Manhattan Republican leader who recruited Rinfret and who was singled out "as one of the most destructive people in this state" by the candidate on Friday.

"Pierre has been under terrible pressure," Goodman said today. "But you have to remember he showed great courage in being willing to make the race when other candidates refused. The single most salient fact about Rinfret is that he stuck his head above the trenches when other candidates would not."

The wealthy 66-year-old economist emerged as a candidate only after it was clear nobody else wanted to run what all agreed would be a futile race against a powerful and popular incumbent. He repeatedly told Republican leaders here he could raise all the money he needed.

But over the past two months, Rinfret has become so irrelevant that Cuomo has ignored him completely, focusing instead on national issues in what many see as yet another act in his endless flirtation with the presidency.

"The worst thing that could happen to Mario Cuomo right now is to have a Democratic state Senate and a Democratic Assembly," said Fred Siegel, a political analyst and historian who teaches at Cooper Union here. "The Democrats want that protective shield, they want to say we couldn't accomplish our goals because the Republicans blocked them. The last thing Cuomo needs right now is to be held accountable."

Democratic officials here, for the most part, have largely chosen to watch the carnage from the sidelines as their opponents try to remain graceful while their standard-bearer intensifies his attacks on them each day.

But they have been delighted to hear Rinfret attack his own party for its willingness to vote for taxes and spending.

"This debacle has given us more credibility," said Tony Massiello (D-Buffalo), chairman of the state Senate campaign committee. "He has highlighted what we have always been saying. In this state, the Republicans are the party of taxing and spending."