If you had asked any savvy politico a year and a half ago to name the likely winner in the 1986 New York Senate race, he probably would have said Geraldine Ferraro. Sure, incumbent Republican Alfonse D'Amato would be tough: he'd worked local issues hard. But New York continues to be one of the nation's most Democratic states, and Rep. Ferraro, the daughter of an Italian immigrant, a housewife and prosecutor, a feminist and the personification of traditional values, seemed an attractive candidate for 1986 long before she was tapped for the 1984 vice presidential nomination.

But there will be no Ferraro-D'Amato race in New York: on Wednesday she announced she isn't running. The reason, she said, was "delays" in a Justice Department investigation of her campaign finances. Yet even apart from that, it was apparent that best- selling author Ferraro, who stood toe-to-toe in debate with the vice president of the United States, would have entered the race as an underdog. She has been trailing in the polls. She lacks an energizing issue. She couldn't claim credibly to be more energetic in pursuit of parochial interests than Mr. D'Amato.

So Alfonse D'Amato, until 1980 presiding supervisor of the town of Hempstead, has made himself a heavy favorite for reelection though he is a conservative Republican in a state that is usually counted liberal and Democratic. Already Elizabeth Holtzman, who came within 1 percent of beating Mr. D'Amato in 1980 in a three-way race, has announced she would not run this year. Leading the list of possible Democratic nominees are a former Nader's Raider who lost a House race in Manhattan, a former head of the state power authority and the former president of the American Stock Exchange.

Mr. D'Amato's popularity should not be overestimated, and it's possible that he could be overtaken by a little-known challenger who puts on a strong campaign. He is hard-working and ebullient, unashamed to go to almost any length to appeal to constituents. But there is no reason to believe that voters have a deep attachment to him. The stepping aside of his best-known challenger, even if for extraneous reasons, spotlights his growing political strength.

The suspense in the 1986 elections is whether the Republicans will lose the Senate. That Reaganish Republican Alfonse D'Amato is a good bet to retain his seat in New York, which almost no one six years ago thought could ever be Reagan territory, is evidence of how the fulcrum in American politics has shifted. Geraldine Ferraro made the headlines, but Alfonse D'Amato may be setting the political trend.