Republicans Perry, Romney 'credible' candidates: Obama

US President Barack Obama says he considers Texas Governor Rick Perry and former Massachusetts Governor Mitt Romney, the two top Republican presidential hopefuls, "credible" candidates to challenge him for the White House in 2012.

Obama made the comments in an interview with NBC News to be broadcast on Monday.

In excerpts of the interview released by the network, Obama said he was not worried about his low job approval ratings in opinion polls. He also said he thinks that anti-government elements of the conservative Tea Party movement are a permanent part of American politics.

With US unemployment still above 9 per cent some 14 months before the 2012 election, Republicans see Obama, a Democrat, as increasingly vulnerable.

"The truth of the matter is, the American people have gone through the worst economic crisis since the Great Depression. And they are understandably impatient," Obama said, according to a transcript provided by NBC.

"And I can say to them, 'Look, all the actions we've taken have been the right actions. If we hadn't taken those actions, things would be much worse.' But the bottom line is, unemployment is still at 9 per cent."

Asked about Perry, who has moved into front-runner status for the 2012 Republican presidential nomination, Obama said: "He's been the governor of a big state. And you know, there's no doubt he's a credible candidate, as is Mr Romney and a whole bunch of other folks."

Obama declined to respond to specific jabs made about him by potential opponents and said he was not concerned about his own position in the polls.

"One of the things that I learned very early on is not to worry about polls, because if I was worrying about polls, I wouldn't be sitting here," he said. "I was down about 30 (percentage) points around this time in my first run for (the) presidency."