Just a month ago in the GOP race, Thompson was in second place with 19 percent. Along with his drop in total support since then, his backing from conservatives also has fallen, though his support from evangelicals and Southerners has stayed roughly the same. In all three categories, he now trails Huckabee.

"You need to be able to have a broader-based conservative coalition" than Huckabee has to win, said John McLaughlin, Thompson's pollster, who said the race remains fluid. "The question is can he broaden? The challenge to the other candidates is can we get a greater share of conservative votes."

Giuliani's national support has barely budged since spring, but his backing from Southerners has fallen since November. He now trails Huckabee in that category, and is about tied with him for conservatives and evangelicals. The AP-Pew polling showed Giuliani trailing in Iowa and New Hampshire and sharing the South Carolina lead with Thompson and Romney.

"While other candidates have gone up and down, the mayor's support has stayed steady and strong," said Giuliani spokeswoman Maria Comella.

A front-runner in the earliest contests until Huckabee caught him in Iowa, Romney has met resistance because of some voters' qualms about his Mormon religion. In a speech Thursday in College Station, Texas, he said while he would never abandon his religious beliefs, his church would not influence his decisions as president.

Evangelicals represent about four in 10 GOP voters nationally, according to the new AP-Ipsos survey. That makes them a crucial Republican constituency, though it also underscores why the more moderate Giuliani remains a strong contender.

Despite Huckabee's strength with evangelical voters, he has had a tougher time building support among less religious Republicans. He had the support of only 14 percent of non-evangelicals in the survey, compared with Giuliani's 31 percent.

"If he's going to be successful in the long run, he has to expand his appeal from social conservatives," said Neil Newhouse, a GOP pollster not affiliated with a presidential candidate. "If he's able to do that, he'll give anybody a run for their money."

The poll involved telephone interviews with 1,009 adults nationally and was conducted from Dec. 3-5. It had an overall margin of sampling error of plus or minus 3.1 percentage points. Included were interviews with 469 Democrats and people leaning Democratic with a margin of sampling error of plus or minus 4.5 percentage points, and 376 Republicans and GOP leaners with a margin of sampling error of plus or minus 5.1 percentage points.

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AP Director of Surveys Trevor Tompson and AP News Survey Specialist Dennis Junius contributed to this report.