US President Barack Obama and his rival Mitt Romney hunted for votes in battleground states Saturday after the Republican challenger propelled the economy to the forefront of the campaign by promising to restore the country's economic engine.

Romney will take his message to Florida voters while Obama plans to defend his record in the northeastern state of New Hampshire.

With just 10 days to go until Americans troop to the polls, the Republican nominee on Friday sought to steal Obama's 2008 "change" slogan and brand him a hapless leader unable to end the slow-growth malaise that has defined the economy.

"The president's campaign falls far short of the magnitude of the times. And the presidency of the last four years has fallen far short of the promises of his last campaign," Romney told a crowd in Ames, Iowa.

Turning the tables on 2008 Obama, the 65-year-old multimillionaire private equity baron billed himself as the hope-and-change candidate and the Democratic incumbent as representing the political "status quo."

"President Obama promised to bring us together, but at every turn, he has sought to divide and demonize. He promised to cut the deficit in half, but he doubled it," Romney said.

Obama had also been in the region Thursday, stumping for blue-collar votes and seeking to shore up a firewall against Romney, who has drawn ahead of the incumbent in national polls but still trails in key swing states.

With the election on a razor's edge, the two teams are readying cross-country travel blitzes over the final 10 days of the campaign.

But Mother Nature is intruding on their plans.

Tropical storm Sandy threatens to barrel ashore along the US Mid-Atlantic coast on Monday, bringing torrential rain and heavy flooding, and potentially knocking out power to millions just one week before the election.

Experts say the storm, downgraded from a hurricane, may collide with a powerful "nor'easter" seasonal weather system and merge with it to form a monstrous super-storm affecting more than a dozen states.

Fears of foul weather have already forced Romney to scrap a Sunday campaign rally in Virginia Beach, Virginia, while Vice President Joe Biden canceled a Saturday appearance in the same city to allow officials to focus on storm preparations.

The White House said it was monitoring the storm closely, and Obama received a briefing on Friday from top emergency officials.

Aside from the threat to millions of residents, the storm could upend election-related preparations across several states, interfere with early voting, and cause problems at polling stations.

Meanwhile the government released data showing economic growth picked up steam in the third quarter, reaching an annual pace of 2.0 percent.

The rate was a little better than had been expected but Romney called the news "discouraging," saying growth was less than half what had been predicted by the White House when it passed the 2009 stimulus bill.

"Slow economic growth means slow job growth and declining take-home pay. This is what four years of President Obama's policies have produced," he said.

Romney boldly predicted to a crowd of 2,500 people in Iowa that he could get the economy galloping ahead at four-percent growth.

"We are at a turning point today. Our national debt and liabilities threaten to crush our future, our economy struggles under the weight of government and fails to create essential growth and employment," he said.

Team Obama quickly attacked Romney for peppering his speech with "dishonest attacks and empty promises of change, but no new policy.

"That's because all Mitt Romney has is a one-point economic plan that he's been running on for two years: the very wealthy get to play by a very different set of rules than everyone else," said Obama campaign spokeswoman Lis Smith.

Heading into the final lap of a months-long race, Romney spent a third straight day in the Midwest, where he has been addressing large crowds and mocking Obama's "incredibly shrinking campaign."

After his Iowa speech he returned to Ohio, where the Republican had spent all day Thursday campaigning. The state is a virtual must-win for Romney; no Republican has clinched the White House without also winning the Buckeye State.

The latest CNN/ORC poll released Friday shows Obama ahead 50-46 percent among likely voters in Ohio, where the campaigns have blanketed the airwaves with tens of millions of dollars in attack ads.

Obama was back in Washington after his own 40-hour, eight-state tour in which he asked Americans to defy the omens of a weak economy and high unemployment by voting for his re-election.

He spent the day campaigning from the White House, where he launched a media blitz of sorts with 10 interviews Friday, including a half-hour live session with youth-oriented MTV.

In that conversation, Obama repeated that he believes gay couples should be able to marry, but would not push for new federal legislation legalizing same-sex marriages in a second term.

"Historically, marriages have been defined at the state level," the president said. "For us to try to legislate federally is probably the wrong way to go."