COLUMBUS, Ohio (AP) - President Barack Obama and Republican Mitt Romney are pitching to college students and working-class voters in Ohio less than a week before early voting kicks off in this critical Midwestern state.

Fresh off a high-stakes address before world leaders at the United Nations, Obama is set to address rallies Wednesday at two state universities, hoping to generate the kind of enthusiasm among young voters that helped fuel his victory four years ago. Romney plans three stops in major metropolitan areas of the state as part of a bus tour geared toward drawing a contrast with Obama on middle-class economic issues.

Both candidates recognize how critical Ohio's 18 electoral votes will be this fall. Losing here would dramatically narrow Romney's paths to the 270 electoral college votes required to win the White House - and no Republican has ever lost Ohio and won the presidency.

Buoyed by signs of an improving economy, Obama has the edge in polls in Ohio six weeks out from Election Day. The president has led Romney in a series of recent surveys in the state, with a Washington Post poll on Tuesday showing Obama with a lead that was outside the poll's margin of error and a CBS/New York Times poll also showing Obama ahead here. Even on handling of the economy, where Romney until recently has had an advantage, Obama now leads.

Working to close the gap, Romney's campaign released a new, minute-long ad on Wednesday, featuring Romney speaking straight to the camera and acknowledging his opponent's good intentions. "President Obama and I both care about poor and middle-class families. The difference is my policies will make things better for them," the Republican nominee says in the ad. Republicans wouldn't say where they planned to run the ad.

Ohio has become a focal point for the two candidates on the airwaves, with even more TV ads airing here than in expansive Florida. And with early voting set to begin in Ohio on Oct. 2, time is running out for Romney and Obama to make their cases to maximum effect.

The candidates exchanged barbs Tuesday over trade policies with China, an implicit struggle for votes from working-class voters whose livelihoods have been affected by competition from Chinese manufacturers.

"When people cheat, that kills jobs," Romney said at a rally Tuesday afternoon in Vandalia, near Dayton. "China has cheated. I will not allow that to continue."

In a statement, Obama campaign spokeswoman Ben LaBolt criticized Romney's own investments in Chinese companies. "How can we trust Mitt Romney to stand up to China when he profits from China breaking the rules?" he said in a statement.

The Obama campaign said the president planned to highlight his record on China during his Wednesday visit to Bowling Green State and Kent State universities. The campaign said the president has brought more trade cases against China in one term than President George W. Bush did in two.

The Obama administration filed a complaint this month with the World Trade Organization over Chinese subsidies to its auto and auto parts industries, the latest in a series of actions dating back to 2009 to protest what U.S. manufacturers say are the unfair advantages China gives its own companies.

Romney is promising an aggressive course on China as well. In particular, he has vowed to issue an executive order in his first day in office labeling China a currency manipulator, a designation that would trigger negotiations between the two countries and could ultimately lead to U.S. trade sanctions against China. The Obama administration has not been willing to take that step, which is opposed by the U.S. Chamber of Commerce.

Ohio's automobile and manufacturing industries compete with their Chinese peers, leading to widespread resentment over perceived trade transgressions by Chinese companies and their government. The issue has emerged as a central theme in House races, as well as in the state's competitive Senate race.

For Romney, Ohio was fraught because of the state's better-than-average economy. The jobless rate in Ohio stands at 7.2 percent - almost a full percentage point lower than the national average. Romney and other Republicans credit Ohio's Republican governor, John Kasich, but the good news undermines Romney's pitch that Obama's policies aren't working.

Obama's visit on Wednesday marks his 13th trip to Ohio so far this year, his campaign said. And as Romney was making his way to Ohio on Tuesday, Obama unveiled a new campaign ad titled "Fair Share" that seeks to remind voters that Romney paid a lower tax rate in 2011 - just over 14 percent - than many middle-class families. The ad will air in Ohio and seven other competitive states.

Romney has visited the state 10 times since May 1, his campaign said, with an additional seven visits during the primary campaign.

Democrats, hoping to neutralize Romney's Ohio swing with a bus tour of their own, worked to keep alive comments Romney made in a secretly recorded video about how almost half of Americans see themselves as victims and are unwilling to take responsibility for their lives. They also dispatched former Ohio Gov. Ted Strickland to make the case that Romney is "writing off the middle class."