WASHINGTON, Dec. 3 (Xinhua) -- Illustrating the fluid nature of the 2008 U.S. presidential race, front-runners of both parties' candidates have been overtaken in a new poll.

    The Democratic national front-runner Sen. Hillary Clinton of New York was caught up by Sen. Barack Obama of Illinois, according to the Des Moines Register's new Iowa Poll released Monday.

    The Des Moines Register is a leading local newspaper in Iowa, where the first votes of the U.S. presidential race will be cast on Jan. 3 next year.

    Obama leads for the first time in the Register's poll as the choice of 28 percent of likely voters, up from 22 percent in October.

    Clinton was the preferred candidate of 25 percent, down from 29percent in the previous poll.

    Former Sen. John Edwards of North Carolina held steady with 23 percent, in third place, but remained part of the three-way battle.

    On the Republican field, Mike Huckabee of Arkansas has leaped ahead of Republican presidential rival Mitt Romney of Massachusetts in Iowa, seizing first place in another recent poll.

    Huckabee wins the support of 29 percent of Iowans who say they definitely or probably will attend the Republican Party's caucuses on Jan. 3.

    Romney, who has invested more time and money campaigning in the state than any other GOP candidate, finished second place with the backing of 24 percent.

    Former New York mayor Rudy Giuliani, the front-runner in national polls, holds third place in Iowa at 13 percent.

    Thompson, a former U.S. senator from Tennessee who waited until September to formally enter the race for the Republican nomination, has slipped to fourth place in the Iowa Poll, at 9 percent.

    Sen. John McCain of Arizona and U.S. Rep. Ron Paul of Texas are tied for fifth place at 7 percent each.

    Despite the movement, the race for 2008's opening nominating contest in Iowa remains very competitive, with over half of likely voters who favor a candidate saying they could change their minds.