(Corrects fifth paragraph to clarify that a Republican has not won top statewide offices of governor or U.S. senator in more than a decade)
By Keith Coffman
DENVER, Feb 26 (Reuters) - A Republican congressman will give up his safe seat in the U.S. House of Representatives to challenge incumbent U.S. Senator Mark Udall this fall, a move that could improve the party's odds of unseating the first-term Democrat, a top Colorado Republican official said on Wednesday.
Representative Cory Gardner, a two-term U.S. House member who represents a conservative district in eastern Colorado, enters the primary race along with several GOP candidates who are vying for the Senate nomination, although none have his name recognition in the politically divided state.
Gardner will formally announce his Senate bid this weekend, according to a Republican party official, who declined to give his name before the formal announcement. The news, which was first reported by the Denver Post, prompted considerable jockeying among both Democrats and Republicans, as one contender announced he was withdrawing from the senate race to run instead for Gardner's congressional seat.
"This completely changes the dynamic of the race," said Floyd Ciruli, an independent Denver political pollster. "Gardner will be attacked by for being extreme, but he is an affable candidate who can come across as center-right."
A Republican has not won a statewide election to be governor or a U.S. senator in Colorado in more than a decade. But Udall, 63, is perceived as vulnerable over his support for the Affordable Health Care Act, which is unpopular in Colorado, Ciruli said.
His main GOP rival until Wednesday, Weld County District Attorney Ken Buck, could not match Udall's fundraising prowess. He bowed out of the race on Wednesday and endorsed Gardner, saying he would instead seek the House seat vacated by the congressman.
"The Senate race has never been about me but about helping change the direction of the country," Buck said in a statement. "I hope to have the opportunity to lead the fight for limited government and fiscal responsibility."
A Quinnipiac University poll released this month showed Udall with a slim three-percentage point lead over Buck, but he dwarfed the prosecutor in fundraising.
Now that Gardner is in the race, the money will start flowing, Ciruli predicted, noting that Udall has amassed $5 million so far in his re-election war chest. Buck, campaign contribution records showed, had raised just $379,000 by the end of last year.
"Republican donors have been looking for a serious candidate to take on Udall," he said.
Rick Palacio, chairman of the Colorado Democratic party, wasted no time in taking on Gardner, calling him a "radical who is neck deep in Washington sleaze. ...
"Gardner is just another reckless House Republican when it comes to dismantling Social Security and Medicare, banning abortion and many types of birth control, and irresponsibly putting our economy at risk to advance his political agenda," Palacio said in a statement released Wednesday.
Udall is the son of the late Morris "Mo" Udall, a former U.S. Congressman who sought the Democratic presidential nomination in 1976.
His cousin, Tom Udall, is a first-term Democratic Senator from New Mexico. (Editing by Sharon Bernstein; Editing by Ken Wills)