(Reuters) - Republican presidential frontrunner Mitt Romney has taken the lead in Iowa, which holds its caucuses in six days, and Rick Santorum is surging, according to a new poll commissioned by CNN and Time magazine.

Romney, the former Massachusetts governor whose unsuccessful presidential run in 2008 took a heavy hit when he lost Iowa, was at 25 percent of the vote, 3 points ahead of Texas Rep. Ron Paul.

Santorum, a former Pennsylvania senator and social conservative, has moved into third place, earning the vote of 16 percent of Iowa voters surveyed by the news organizations six days before the caucuses kick off the 2012 election cycle on Jan. 3.

Santorum's suddenly strong standing is a blow to the fortunes of Paul, who had been leading in many Iowa polls.

We've always felt like we could trust the people of Iowa, Santorum told CNN in an interview.

In recent weeks, party watchers have wondered which candidate would win the votes of Iowa's many evangelical voters.

Santorum received the endorsement of one of the state's top Christian Right leaders, Bob Vander Plaats of The Family Leader group.

The poll surveyed 457 registered Republicans who are likely to attend the caucuses. Paul's campaign counts as key to its strength its ability to attract Democrats and independents, who can participate in the caucuses if they enroll in the Republican Party on Jan. 3.

In the CNN interview, Santorum criticized Paul's record as a legislator.

Ron doesn't have a very long record of actually passing anything in Washington, D.C., Santorum said.

(Reporting By Samuel P. Jacobs)