Washington ? Dig beneath the surface of the raucous Republican presidential race and you will find even deeper turmoil: Four in 10 GOP voters have switched candidates in the past month alone, and nearly two-thirds say they may change their minds again.

Mike Huckabee, who has roared to a tie with longtime front-runner Rudy Giuliani, has little reason to feel safe, according to an ongoing national survey conducted for The Associated Press and Yahoo News.

Half of all voters – including four in 10 Republicans – know too little about Huckabee to even say whether they have a favorable impression of him, let alone whether he is conservative, liberal or moderate. That could be ominous, because it gives his rivals the opportunity to define him. Witness Mitt Romney’s criticism of the former Arkansas governor on immigration and Fred Thompson’s contention that he raised taxes “like a Democrat.”

The Democratic side is less chaotic, with Hillary Rodham Clinton maintaining a clear lead nationally over Barack Obama, though voters are still doing plenty of shifting. About one in five backs a different contender than in November, and nearly half say they still may settle on someone else, according to the poll conducted by Knowledge Networks.

This ground-level view of the 2008 race is made possible by an AP-Yahoo News survey that will periodically question the same 2,000 people until Election Day, repeatedly seeking their views about politics, the country and their own lives. That will produce a picture of how the campaign is playing out from the perspective of voters like Matthew Larson, 29, of Mankato, Minn., who since last month has moved from Giuliani to Huckabee.

“I switched due to inconsistencies in Giuliani’s stands” on abortion, said Larson, a security counselor, referring to the former New York mayor’s explanations of his abortion rights views that trouble many. “That’s the big one in our household. Huckabee just seems more firm in what he wants to do.”

Highlighting how restless Republicans are, a fifth who said last month they wouldn’t change candidates did so anyway – along with half who said they might change. Only a third of Democrats who said they might change moved to a different contender.

People’s drifting sentiments even pushed them across party lines, with 14 percent changing their loyalty as Democrats, Republicans or independents in roughly equal proportions. Among them was Anne Marie Pontarelli, who shifted from the GOP to Clinton because she liked her equivocal initial response to the controversy over states granting driver’s licenses to illegal aliens.

“There are many shades of gray” on issues, said Pontarelli, 30, a consultant from Downers Grove, Ill. “The way she responded took a lot of guts.”

No one in the GOP had a rougher ride in the past month than Thompson, the former Tennessee senator who joined the race in September and has slowly fizzled ever since. This month’s poll showed he retained just over half of those who supported him in November, compared with six in 10 by Giuliani, Romney and John McCain and three in four by Huckabee.

Among Democrats, Clinton’s large lead over Obama and John Edwards changed little, though polls on Iowa’s Jan. 3 caucuses – the nation’s first voting – show them in a three-way battle there.

Nationally, six in 10 Obama supporters now say they are sure to stay with him, a gain from last month and the same as for Clinton. Edwards’ certain supporters doubled, but only to just more than four in 10.

“She’s kind of harsh,” Linda Beerhorst, 56, a notary from Osceola, Ind., said of Clinton, whom she has abandoned for Obama. “He doesn’t talk like a politician, he talks like your next-door neighbor.”

The survey of 1,821 adults was conducted from Dec. 14-20, and had an overall margin of sampling error of plus or minus 2.3 percentage points. Included were interviews with 847 Democrats, for whom the margin of sampling error was plus or minus 3.4 points, and 655 Republicans, with a margin of sampling error of plus or minus 3.8 points.