DES MOINES, Iowa — Mitt Romney has regained the lead among Republicans in the race to win Iowa's GOP presidential caucus on Thursday, as Mike Huckabee has lost momentum and support, even among the evangelical Christians who had propelled him into the top spot just weeks ago.

At the same time, John Edwards has clawed his way into contention in the Democratic Party caucus, gaining strength even as his rivals for the presidential nomination, Hillary Clinton and Barack Obama have lost ground, according to a new McClatchy-MSNBC poll.

Taken together, this first poll in Iowa since campaigning resumed after a Christmas break showed a dead-heat contest between the three leading Democratic candidates and a volatile clash between the two top Republican rivals here.

"On the Democratic side, the race is about as close as it can get, but keep an eye on Edwards," said Brad Coker of Mason-Dixon Polling & Research, which conducted the survey of 400 likely Democratic caucus attendees and 400 likely Republican caucus attendees in Iowa was conducted by telephone from Dec. 26-28. "Edwards has really moved up since our last poll. Obama and Clinton have each slipped a little bit."

The new survey, taken Dec. 26-28, came three weeks after the initial Dec. 3-6 poll.

On the Republican side, Coker said, "Romney has rebounded and the Huckabee bubble may have burst.

"Last time, Huckabee was getting all the good press and nobody had put him under any scrutiny.... Now he's under the spotlight, and he's started to wilt a little."

Among Republicans:

—Former Massachusetts Gov. Romney has 27 percent

—Former Arkansas Gov. Huckabee has 23 percent

—Former Tennessee Sen. Fred Thompson has 14 percent

—Sen. John McCain of Arizona has 13 percent

—Former New York Mayor Rudy Giuliani has 5 percent

—Rep. Ron Paul of Texas has 5 percent

—Rep. Duncan Hunter of California has 1 percent

—Undecided: 12 percent

One in three Iowa Republicans say they could still change their minds.

No one knows that better than Huckabee, who surged into the lead three weeks ago and now has lost it just as quickly. Huckabee's support dropped 8 percentage points since the last McClatchy/MSNBC poll Dec. 3-6.

A major reason why is that he's come under sharp criticism from rivals such as Romney, been blistered as a tax raiser in a $500,000 ad campaign aired by the anti-tax group Club For Growth, and faced new scrutiny by the media of his Arkansas record on such issues as pardons.

He still ranks tops among Iowa Republicans who rank values and family issues their top concerns.

But while the ordained Baptist preacher still leads among the state's influential evangelical Christians, he's lost 8 points among them.

Romney, who had led in the state for months before dropping to second place, regained 7 points since early December.

Iowa Republicans gave him their highest favorable rating, and he ranked first among GOP voters looking for experience, leadership and the ability to win in November. He also led among voters who ranked immigration, taxes or terrorism their top concerns.

A key gain: He now has the support of 27 percent of the state's evangelical Christian Republicans, up sharply from 8 percent several weeks ago. Concerns about his Mormon faith appear to have ebbed.

One warning sign for Romney: one-third of his supporters say they still could defect to a rival, while only 22 percent of Huckabee's backers say that.

Among Democrats:

—Edwards, the former U.S. senator from North Carolina, has the support of 24 percent

—Sen. Clinton of New York has 23 percent

—Sen. Obama of Illinois has 22 percent

—Gov. Bill Richardson of New Mexico has 12 percent

—Sen. Joe Biden of Delaware has 8 percent

—Sen. Chris Dodd of Connecticut has 2 percent

—Rep. Dennis Kucinich of Ohio has 1 percent

—Undecided: 8 percent

One in five Iowa Democrats say they could still change their minds. The poll's margin of error was plus or minus five percentage points.

While the survey shows a virtual statistical tie, it also shows Edwards with some momentum heading into the final days. He's gained 3 percentage points since McClatchy-MSNBC polled Iowa before the holidays, while Clinton lost 4 points and Obama lost 3 points.

Also gaining were Richardson and Biden, each picking up 3 points.

The second tier is particularly important in Iowa's Democratic caucuses, where a candidate can win delegates only if they register at least 15 percent support in each town hall-like precinct meeting. Voters whose candidates don't make that threshold can support someone else.

As of now, that appears to help Edwards.

If all second-tier Democratic candidates fall short and their supporters switch to other candidates, Edwards gains the most, rolling up a clear lead at 33 percent to 26 percent each for Clinton and Obama.

Edwards, pushing a people-versus-the powerful message, owes his gains to voters looking for a general election winner, someone who agrees with them on the issues, and those who rank Iraq their top concern. Key demographic slices for him include men and union members.

Of note: more Iowa Democrats have a favorable impression of him — and fewer have an unfavorable impression of him — than any other candidate.

Clinton owes her solid standing to strong support from women, voters over age 50, and Democrats who rank health care as their top issue and experience as the most important personal characteristic.

A warning sign: One in five Iowa Democrats have an unfavorable opinion of her, and she ranks low among voters looking for honesty and change.

Obama has the edge among young voters under 30, those looking for a new approach to politics, and honesty. His challenge: low support among those valuing experience most, and convincing people he can win.

Meanwhile, the new McClatchy-MSNBC poll shows the assassination of former Pakistani Prime Minister Benazir Bhutto did not raise the profile of terrorism as an issue in the U.S. presidential campaign in Iowa.

"People are still voting on what they were voting on a week ago," said Coker, the Mason-Dixon Polling & Research pollster.

Democrats still rank terrorism a very low priority. The survey found 5 percent of Iowa Democrats calling it their top concern, up from 1 percent earlier in the month, but with virtually no change during three nights of poll calls that started the evening before the assassination and continued the next two evenings when news of the murder dominated national media.

Republicans still rank it highly, with 29 percent calling it their top issue, down from 31 percent in the previous poll Dec. 3-6.