Republicans yesterday criticized Democratic vice-presidential candidate Joseph R. Biden Jr. over an overheard comment at odds with Illinois Sen. Barack Obama's campaign pledge to support the development of clean coal plants in the United States.

In the remarks, circulated on YouTube, the Delaware senator seems to reject the idea of building new coal-fired plants domestically, while suggesting that clean-coal technology, a goal that both campaigns have promised billions of dollars to develop, should be used to protect the environment from coal plants abroad.

In the video, recorded at the beginning of Mr. Biden's bus trip across Ohio last week, the Democrat is speaking to a woman as he works the crowd after a rally. Responding to her question pressing him on why the campaign is supporting clean coal, he says: "We're not supporting clean coal. Guess what? China is building two every week, two dirty coal plants. And it's polluting the United States, it's causing people to die."

As their exchange continues, Mr. Biden says: "China's gonna burn 300 years of bad coal unless we figure out how to clean their coal up, because it's gonna ruin your lungs, and there's nothing we can do about it. No coal plants here in America. Build 'em, if they're gonna build 'em, over there and make 'em clean because they're killing you."

Arizona Sen. John McCain's campaign jumped on the remarks. The Republican nominee criticized them yesterday during an Ohio campaign stop, while his aides staged at least two conference calls allowing coal-state Republicans to register their opposition.

"My opponent is against the expansion of nuclear power," Mr. McCain said, repeating a charge contradicted by Mr. Obama's repeated remarks on the issue. "His running mate here in Ohio recently said that they weren't supporting clean coal either."

Mr. McCain has more enthusiastically supported developing new nuclear plants, but Mr. Obama, in his platform and in numerous remarks on the issue, has voiced at least cautious support for nuclear power. The candidates differ on the location of a radioactive waste storage facility under development in Nevada. Mr. McCain supports it; Mr. Obama opposes the site, while not offering an alternative.

Both presidential candidates have pledged to support research that would allow the burning of coal while capturing its greenhouse-gas emissions -- a pledge seemingly contradicted by Mr. Biden's remarks.

In a call yesterday with Pennsylvania reporters, Rep. Phil English, R-Erie, characterized those comments as "Senator Biden's bizarre anti-coal rant." And Rep. Mike Turzai, R-Bradford Woods, said they were "a slap to those [coal mining] employees and a slap to consumers who want electric consumption at realistic prices."

Without specifically addressing Mr. Biden's "no coal plants here in America" passage, an Obama campaign spokesman insisted in a statement, "This is yet another false attack from a dishonorable campaign."

"Senator McCain knows that Senator Obama and Senator Biden support clean-coal technology. Senator Biden's point is that China is building coal plants with outdated technology every day, and the United States needs to lead by developing clean-coal technologies," spokesman David Wade said in the statement. "The Obama-Biden comprehensive energy plan will invest $150 billion over 10 years in clean energy technologies, including incentives to accelerate private-sector investment in commercial-scale zero-carbon coal facilities."