Texas Gov. George W. Bush could be buying himself trouble in a general election with his proposal for a substantial tax cut, but he is betting that the issue will work for him where it counts now: when New Hampshire holds the nation's first primary.

A new Washington Post-ABC News poll in New Hampshire found that the tax issue has risen sharply in importance among Republican voters and that Bush holds a substantial lead among those who say it will be the principal issue in determining how they vote Feb. 1.

The raging tax debate between Bush, Arizona Sen. John McCain and magazine publisher Steve Forbes comes at a time of transition among Republicans on an issue that has defined the party for the past two decades.

McCain hopes to push the party away from its love affair with deep cuts in marginal tax rates, and his advisers argue that a growing number of Republicans would rather see modest tax cuts and more emphasis on saving Social Security.

With the economy strong and the federal budget producing huge surpluses, there is clear sentiment in the country to deal with Social Security and Medicare before cutting taxes. Although Republicans still strongly favor tax cuts, Andrew Kohut of the Pew Research Center said, "I've been struck that even among people who think of themselves as Republicans, given choice of cutting taxes and fixing Social Security, they opt for fixing Social Security."

A recent Time/CNN poll found that three in five Republicans said they preferred a modest tax cut, accompanied with more money going toward Social Security, to a bigger tax cut and less spending on the government-sponsored retirement plan.

After repeated defeats at the hands of President Clinton, Republican confidence in big tax cuts as a political weapon may be weakening. Robert J. Dole got nowhere against Clinton in the 1996 campaign with his tax proposal. Congressional Republicans have scaled back their aspirations this year after losing a showdown with Clinton over a 10-year, $792 billion tax cut.

One Republican strategist, who asked not to be identified, said: "I think the number of people who really want a tax cut has slipped a bit. Maybe the priority has slipped a bit, but the basic attitude has not."

The strategist said that "another strain of conservatism" puts greater emphasis on reducing the debt and that protecting Social Security resonates with many older Republicans.

That could spell trouble for Bush, if he becomes the Republican nominee, because he has put forward a $483 billion proposal that is nearly double the size of McCain's and gobbles up most of the non-Social Security surplus over five years. Already, he has come under attack from Vice President Gore, and if the general election pits Gore against Bush, the Texan's tax plan will become a target for Democrats.

But Republican analysts say the tax cut issue remains an article of faith among party activists--those most likely to vote in primaries or caucuses. "It's stronger than ever as kind of a core issue for Republicans," said GOP pollster Ed Goeas. "When you ask overall numbers what's the most important problem, it doesn't surface. But show me someone who doesn't have strong feelings about the taxes he pays and I'll show you someone who is not a Republican."

A month ago, a Post-ABC poll of all New Hampshire voters found that taxes ranked fifth among eight issues. In the latest poll, it ranks second, behind Social Security and Medicare.

But among likely Republican voters in New Hampshire, the tax issue is now most important in determining how people will vote. The new Post-ABC poll found that 26 percent of New Hampshire Republicans picked taxes as their top issue. Social Security and Medicare rank second at 17 percent. Campaign finance reform, McCain's primary issue, ranks last among eight issues at 4 percent.

Overall, McCain leads Bush 40 percent to 36 percent among New Hampshire Republicans, within the margin of error. But Bush holds a clear advantage among the quarter of the GOP electorate seeing taxes as important, leading McCain among that group 45 percent to 26 percent. Forbes, who has staked much of his candidacy on a flat tax plan, runs third among that group with 20 percent.

Among those New Hampshire Republicans who say Social Security and Medicare rank as most important, McCain leads Bush 43 percent to 34 percent, with Forbes at 11 percent.

McCain's advisers dispute the idea that Bush's plan is more popular than what they call their candidate's more balanced approach and say proof will come in the primaries, not in polls.

"I can't tell you there's a history that says here's where someone who ran on a larger tax cut versus smaller tax cut didn't win," McCain pollster Bill McInturff said.

But he added that Republicans have never before debated taxes after a seven-year economic expansion and the election of a GOP Congress. "In other words, the stars are aligning in a way that's radically different . . . and that is the base on which you try a different idea," he said.

McInturff also argued that Bush has retreated from his advocacy of a big tax cut, with recent ads talking about protecting Social Security. "What it says to me is they don't have the courage of their convictions," he said.

The Texas governor's advisers believe the tax issue will be decisive in determining the GOP nomination, but Bush's gamble on big tax cuts could become a case of winning the battle of January and February but losing the war in November.

Assistant polling director Claudia Deane contributed to this report.