Mitt Romney aims to reignite his struggling White House bid Tuesday with a bus tour through Ohio, where he vows an aggressive tack against a surging President Barack Obama six weeks from election day.

Romney drew criticism last week for spending more time fundraising than at public campaign events. Tuesday marks an opportunity for the Republican nominee and his running mate Paul Ryan to reach out directly to voters in one of the election's most prized battlegrounds.

Obama's challenger is returning to the stump pushing his economic message on the back of last week's opprobrium for his comments belittling "47 percent" of Americans as government-dependent freeloaders.

After trying to draw a line under his 47 percent comments, insisting he would be a president who worked for all Americans, Romney sought to reassure voters he and Ryan were "very anxious to get out and speak with as many people as we can."

"We hit the road pretty darn hard," Romney told ABC News after a campaign appearance in Colorado on Monday.

Romney also insisted he was headed for election day victory despite polls showing him the underdog and Obama breaking the important 50-percent approval threshold in some battleground states, any of which could decide the November 6 election.

"I'm very pleased with the fact that we have a campaign that is taking our message to the people across America and look, we're going to win," Romney told NBC News, in the second in a series of quick hit interviews with US networks Monday.

"There is no question in my mind. We're going to win."

Ohio and Florida are seen as the two monumental battlegrounds of 2012, and after a handful of events in the Sunshine State late last week, he completes the final two days of the "Romney Plan For A Stronger Middle Class" tour through Ohio.

"This is ground zero," Republican National Committee chairman Reince Priebus, acknowledging the importance of the Buckeye state, told a crowd of about 1,200 people as they awaited Ryan, who kicked off the tour Monday in Lima, Ohio.

Ryan lashed Obama for what he said was four years of economic failure, citing 43 straight months of unemployment above eight percent.

The US economy is "barely limping along, and the president has no idea how to grow it," Ryan said, adding that Romney, a multimillionaire former businessman, has the know-how and experience to turn around the flagging economy.

Ohio, where Obama prevailed in 2008, is pretty much a must-win for Romney; no Republican has ever been elected president without winning the state, and Obama is currently ahead by four percentage points here, according to a RealClearPolitics average of polls.

The president is zeroing in on Ohio as well, and campaigns in the state Wednesday at the same time as Romney.

But first Obama has global business to tend to: addressing the United Nations General Assembly Tuesday in New York, where he will lead Western demands for action on the Syrian civil war and likely address mounting fears of a military strike on Iran.

Romney has no UN role but refuses to be ignored, and before Ohio he too is in New York Tuesday to address the Clinton Global Initiative, president Bill Clinton's forum for leaders to help forge solutions to global problems.

"He's going to hit on... trade, aid and fostering freer markets in developing countries," Romney senior adviser Ed Gillespie said Monday.

Both Romney and Obama have campaigned multiple times in recent months in Ohio, where they face tricky tests, said Mack Mariani, a political science professor at Xavier University in Cincinnati.

The state's north is dotted with industrial factories and steelworkers, while eastern Ohio is coal country. Central Ohio is farmland, while the southern counties are culturally affiliated with the American South, across the river in Kentucky.

"It's a microcosm of all the problems that... America faces," Mariani told AFP.