The well-respected poll was conducted Tuesday through Friday and has Romney, the former Massachusetts Gov. with 24 percent; Texas Congressman Ron Paul with 22; and 15 percent for former Pennsylvania Sen. Rick Santorum who has been surging at just the right time.
However in a sign of the highly volatile nature of the race, 41 percent of likely caucusgoers say they could still change their minds before Tuesday night's vote.
The poll of 602 likely Republican caucusgoers has a margin of error of plus or minus 4 percentage points.
The first-in-the-nation Iowa caucuses, which take place Tuesday evening, kick off voting in the presidential nominating process. The Iowa Poll, a Register exclusive since 1943, is a much-watched indicator of how candidates are faring in the leadoff caucus state.
The first three Iowa Polls of the 2012 caucus cycle, conducted in June, October and November, featured a different leader each time: first Romney, then retired business executive Herman Cain, then Gingrich. Other candidates took turns in the top tier, too. Bachmann was in second place to Romney in the June poll and won the Iowa straw poll in August. But her support plummeted this fall.
Gingrich surged to the lead with 25 percent support in the late November poll, but slid to 12 percent in the new poll.
Now, it’s Santorum’s time to rocket to the top tier. He has campaigned in Iowa more than any other candidate, stumping the state more than 100 days and conducting more than 300 events since the last presidential election. Next closest is Bachmann, at 80 days.
But until recent weeks, Santorum has struggled to escape single digits in state and national polls. He has campaigned as both a strong fiscal and social conservative, but social conservative voters had remained undecided or split among several candidates.
Romney campaigned lightly in the state until December, but he benefits from the network he built as a candidate four years ago, when he campaigned constantly and poured $10 million into a heavy advertising schedule and a big campaign organization.
Jake Gibson is a producer working at the Fox News Washington bureau who covers politics, law enforcement and intelligence issues.