Before the speech, Perry told South Carolina voters on a conference call that he's ready for a showdown with President Obama.

"I full well believe I'm going to win," he said.

Obama's re-election campaign immediately hit back at Perry after his speech in which the Texan ripped the president's economic record.

"Gov. Perry's economic policies are a carbon copy of the economic policies of Washington Republicans," Obama campaign spokesman Ben LaBolt said, citing Perry's support for "cut cap and balance," tax cuts for all Americans, among other things.

"That's the same approach he took in Texas, where middle class families know his economic record is no miracle - it's a tall tale," he said. "In a Republican field that has already pledged allegiance to the Tea Party and failed to present any plan that will benefit the middle class or create the jobs America needs to win the future, Gov. Perry offers more of the same."

At the same time Perry was rolling out his presidential announcement, his GOP rivals were competing in the Iowa Straw Poll, the first time Republican voters will make their preference known.

Perry's speech was largely a formality, since his top advisers signaled earlier this week he would use the appearance to make his plans official. But his speech threatened to overshadow the Iowa Straw Poll, an important measure of support in the nation's first caucus state, in which former Minnesota Gov. Tim Pawlenty and Minnesota Rep. Michele Bachmann hoped to boost their candidacies.

The RedState Gathering in South Carolina, another key early battleground state, was originally expected to draw about 400 people. But Katon Dawson, a former state GOP chairman and Perry supporter, said news of Perry's planned announcement had drawn many more activists to travel to the event.

"I have never seen this landslide of emotion for a candidacy. I cannot literally keep up with the emails and messages coming into my cellphone," Dawson said. "There is an excitement for Gov. Perry that there just isn't around the other candidates."

After South Carolina, Perry was scheduled to travel to New Hampshire, the first-in-the-nation primary state, then to visit Iowa Sunday.

Perry, 61, would bring significant strengths to a field whose strongest candidate thus far has been Mitt Romney, the former Massachusetts governor.

Eight contenders met for a nationally televised debate Thursday night: Romney, Pawlenty, Bachmann, former Utah Gov. Jon Huntsman, former House Speaker Newt Gingrich, Texas Rep. Ron Paul, former Pennsylvania Sen. Rick Santorum and restaurant magnate Herman Cain.

But so far, none has captured the kind of excitement among conservatives Perry has.

Through three terms as governor, Perry has overseen significant job growth in his state while working to keep taxes low. He was an early backer of the tea party movement and enjoys the support of social conservatives because of his opposition to abortion and gay rights. He is also an evangelical Christian who organized a well-attended prayer rally in his state last week.

Perry is a prodigious fundraiser who has already begun laying the groundwork for a national finance network his supporters say would rival that of President Obama, who is expected to exceed his record-breaking $750 million haul from 2008.

But some Republicans worry that Perry's hard-core conservatism and Texas style may not play well in a 50-state contest, particularly coming so soon after former President George W. Bush's two White House terms. Bush had record low approval ratings when he left office in 2009.

Perry's visit to New Hampshire will be his first of the year and comes soon after a handful of GOP activists in the state went to Texas to encourage him to run. He's expected to meet about 100 activists at a house party hosted by state Rep. Pam Tucker.

Romney has dominated early polling in the Granite State, where he has a summer home on Lake Winnipesaukee and has devoted much of his time so far.

"I don't know how people will take to him," Republican activist Ovide Lamontagne said. "I think he's optimistic he'll be able to build a grass-roots organization fairly quickly. But I don't know what he's like as a candidate on the campaign trail."