WASHINGTON - Republican Mike Huckabee announced on Saturday he would not seek his party's US presidential nomination in 2012, adding uncertainty to the race to pick a challenger to President Barack Obama.

"All the factors say 'go,' but my heart says 'no' and that's the decision that I have made," he said on his Fox News Channel television show.

"My answer is clear and firm: I will not seek the Republican nomination for president this year," Huckabee added.

A former governor of Arkansas, Huckabee had been riding high in some 2012 polls among Republicans. But he had not been raising funds or touring the country as he wrestled over whether to launch a second run for his party's nomination or stick with his Fox show Huckabee.

Huckabee, who unsuccessfully sought his party's presidential nomination in 2008, said he had his family's full support, promising poll numbers and evidence he could carry states beyond the US South and appeal to voters beyond social conservatives.

But he said private reflection on his decision to stay out of the race gave him a "clarity and an inexplicable inner peace".

Obama, a Democrat, was far ahead of all possible Republican candidates mentioned in a Reuters/Ipsos poll this week. A number of high-profile Republicans have either declined to run or are still weighing their options.

Former Massachusetts Governor Mitt Romney is expected to run, as is former Minnesota Governor Tim Pawlenty, who analysts say would attract the kind of evangelical, conservative voters who would have backed Huckabee.

Pawlenty said in a statement that "Mike and I agree our nation is facing big challenges and desperately needs new leadership and I plan to work hard to earn the support of the millions of Americans who have supported him".

Former House of Representatives Speaker Newt Gingrich became a candidate this week, along with a number of long-shots, including libertarian-minded Texas Representative Ron Paul.

Still on the fence are Indiana Governor Mitch Daniels, former Alaska Governor Sarah Palin and Minnesota Representative Michele Bachmann.

Wednesday's Reuters/Ipsos survey showed 45 percent of Americans believed Obama would win re-election, a 10-point rise from a poll taken before November's congressional elections.

Reuters