By Lily Kuo
WASHINGTON (Reuters) - Newt Gingrich leads other Republican presidential candidates in the key state of Iowa but his support could be slipping, according to a University of Iowa poll released Monday.
Gingrich, a former speaker of the U.S. House of Representatives, had the support of 29.8 percent of those likely to vote in the Iowa caucuses on January 3.
Mitt Romney, a former governor of Massachusetts, ran second at 20.3 percent in the Hawkeye Poll and Texas congressman Ron Paul had 10.7 percent. U.S. Rep. Michele Bachman had 8.5 percent, followed by Texas Governor Rick Perry with 8.2 percent.
Thanks in part to good performances in candidate debates, Gingrich has enjoyed a quick jump to the top of opinion polls in Iowa, South Carolina and Florida, which vote early in the state-by-state nominating process.
Gingrich has cast himself as a more conservative alternative to Romney, who had been the longtime frontrunner in the race to determine who will face Democratic President Barack Obama in the 2012 elections.
The Iowa poll suggests that Gingrich's lead in that state could be fading.
It was conducted over a weeklong period in which another conservative candidate, Herman Cain, suspended his campaign amid allegations that he had a 13-year extramarital affair.
In the early part of the polling period before Cain dropped out on December 3, Gingrich was receiving 37.7 percent support. After Cain's exit toward the end of the polling period, Gingrich's support was down to 24.4 percent.
Gingrich's overall 29.8 percent average for the week still was enough for him to lead the poll comfortably but "our results show that his support may be starting to slide, as it has with previous frontrunners," said Frederick Boehmke, an associate professor of political science at Iowa and an adviser to the Hawkeye Poll.
Cain led the previous Hawkeye Poll, which was released on October 21. As Cain's lead in Iowa melted away, much of his support there appeared to go to Gingrich.
However, Boehmke said, Gingrich's apparent dip after Cain's withdrawal indicates that Gingrich -- who has run a non-traditional campaign with few staff members and an emphasis on television appearances -- eventually could be hurt by his lack of an organization in Iowa.
"Gingrich has spent little time" in Iowa, Boehmke said. "While Gingrich is polling well, his minimal staff and grassroots organization in Iowa suggest he may be unable to turn out supporters on January 3 to the same degree as the others."
The Hawkeye Poll found that Gingrich's lead over Romney was weakest among respondents who said they were "very likely" to attend the caucuses.
In the 2008 Iowa Republican caucuses, Romney spent millions of dollars reaching out to voters, only to lose to Mike Huckabee. In a state that values personal campaigning, Romney eventually could have an advantage over Gingrich, analysts say.
"Among here the candidate who has spent the least amount of time in Iowa and has the least amount of organization is Gingrich," said Caroline Tolbert, co-author of the 2011 book, Why Iowa? "Romney's support may be more solid."
In the survey, almost 300 likely Republican caucus goers chose from the list of Republican candidates competing for their party's nomination. The poll's margin of error was plus or minus 6 percent. The poll was conducted from November 30 to December 7.
(Reporting By Lily Kuo; Editing by David Lindsey and Bill Trott)