CINCINNATI — Appealing to Rust Belt voters, President Barack Obama announced a new trade enforcement action against China on Monday, while Republican challenger Mitt Romney planned a greater emphasis on policy details that distinguish him from Obama to stop the incumbent’s election momentum.

Romney’s shift comes as Republicans openly fret about the state of their nominee’s campaign and press him to give voters a clearer sense of how he would govern. In newly published polls, Romney has lost the edge he held over Obama as the candidate better able to handle the federal budget deficit and taxes.

Romney pollster Neil Newhouse attributed Obama’s gains to the bump the president received overall after the Democratic National Convention in North Carolina this month. But on taxes, Newhouse acknowledged Romney’s need to do more to distinguish his plans.

“I’m not sure that voters really understand the differences between the plans Mitt Romney has and Obama has,” Newhouse said. “And I think that’s one thing we’re committed to trying to do in moving forward is defining the differences between the two candidates on taxes.”

One recent line of criticism from Romney appears to have brought a quick response from Obama. The White House announced a move to stop Chinese subsidies of its auto industry — four days after Romney launched an advertising campaign accusing the president of allowing American manufacturing jobs to be lost to the Asian power.

The issue hits home among working class voters in manufacturing swing states such as Ohio, where Obama has gained recently in polls and touted his new action Monday. The White House says more than 850,000 jobs in the state are related to the auto industry.

Obama told thousands gathered at a pavilion in Cincinnati’s leafy Eden Park that Romney made money from companies that outsourced jobs to China while running the private equity firm Bain Capital. The crowd jeered. Obama responded, “Don’t boo. Vote!”

“You can’t stand up to China when all you’ve done is send them our jobs,” Obama said. “You can talk a good game. But I like to walk the walk, not just talk the talk. And my experience has been waking up every single day doing everything I can to make sure that American workers get a fair shot in the global economy.”

Romney responded in a statement accusing Obama of ignoring China for too long. The Republican promised to act from his first day in office to help U.S. businesses compete.

“Campaign-season trade cases may sound good on the stump, but it is too little, too late for American businesses and middle class families,” Romney said. “President Obama’s credibility on this issue has long since vanished.”

Campaign spokeswoman Jen Psaki said it takes “a special kind of chutzpah” for Romney to criticize Obama on China with his record at Bain.

Opinion polls since the political conventions show not only that Obama is leading in the key swing states, but a recent national poll shows he has taken over Romney’s long-standing advantage on the question of whom voters view as most likely to restore the economy and create jobs. Still, the overall race remains narrowly divided.

Romney on Monday was targeting his economic message to Hispanics, a key voting bloc with whom Obama enjoys an advantage. The Obama campaign released an online video riffing on the “Extreme Makeover” television show, mocking Romney for trying to win over Hispanics even though the Obama campaign says the Republican wants to cut education and health care programs that would help them.

“Many Hispanics have sacrificed greatly to help build our country and our economy, and to leave for their children a brighter future,” Romney said in excerpts released before his speech to the U.S. Hispanic Chamber of Commerce in Los Angeles. “Today, those sacrifices are being squandered by a president who cannot stop spending.”

Romney said his test on federal spending would be whether a program is “so critical that it is worth borrowing money from China to pay for it.”

The office of the U.S. Trade Representative announced Monday it has asked the World Trade Organization to intervene with China over illegal subsidies of exports in their autos and auto parts sectors. The U.S. says the practice puts American parts manufacturers at a competitive disadvantage and encourages the outsourcing of production to China.

Jobs in the U.S. auto parts sector dropped by roughly half between 2001 and 2010, while U.S. imports of auto parts from China have increased seven-fold, according to the Obama administration.

The administration is also escalating another case it brought against China at the WTO in July that accuses China of imposing unfair duties on more than $3 billion in exports of U.S. autos. The duties cover more than 80 percent of American auto exports to China, said the officials, who requested anonymity because they were not authorized to discuss publicly details of the trade action before the president announces it.

The cases stem from the Interagency Trade Enforcement Center Obama set up earlier this year to target unfair practices around the world, particularly in China.

Obama and Romney began trading barbs on China late last week.

Romney released a television advertisement Thursday accusing Obama of “failing American workers” and ignoring unfair trade practices by China. In his weekly podcast Saturday Romney said that “in 2008, candidate Obama promised to take China ‘to the mat.’ But since then, he’s let China run all over us.”

Obama countered with a TV spot focused on its claims that Romney outsourced jobs to China while working in the private sector. His campaign also released a new Web video Saturday in which Obama deputy campaign manager Stephanie Cutter said Romney holds investments in Chinese companies.

Romney’s campaign piled on Monday with two new spots: one outlining his plan for job creation and the other assailing Obama for a growing national debt.

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Pickler reported from Washington. Associated Press writers Ken Thomas in Los Angeles, Kasie Hunt in Washington and Thomas Beaumont in Iowa contributed to this report.

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Follow Julie Pace at http://twitter.com/jpaceDC