CAMBRIDGE, Mass. – John McCain and Barack Obama both believe the United States should reduce carbon emissions and cut its oil dependence, but differ on how active a role the government should play in energy policy, their advisors said Monday.

Both presidential candidates are open to drilling for oil off U.S. coasts and would promote investment in technologies to reduce emissions of carbon dioxide that contribute to global warming. But they disagree on how to pay for the changes.

Jason Grumet, an adviser to the Democratic candidate Obama, criticized McCain's approach at a debate at the Massachusetts Institute of Technology, contending that it lacked specifics.

“These are complicated issues, they require complicated answers,” said Grumet, of the Bipartisan Policy Center.

R. James Woolsey, a McCain adviser, said the Republican candidate believes the best approach is for the government to establish a cap-and-trade system that attaches a cost to the emission of carbon dioxide, a greenhouse gas associated with climate change.

“I'd have to admit that Senator Obama's plan is more detailed,” said Woolsey, who served as CIA director during the Clinton administration. “Senator McCain believes we should stick to a general direction such as cap and trade and leave the detailed standards, renewable fuels and so forth, up to local decision makers.”

REFITTING COAL PLANTS

Both candidate would like to convert coal-burning power plants, which provide about half the nation's electricity, so they could capture carbon emissions. The gas would be pumped into underground reservoirs.

“If we were able to in fact develop technology to retrofit the existing fleet of coal plants to capture and store or sequester carbon, that would be the most important single breakthrough the world has ever made when it comes to how we address climate change,” Grumet said.

Obama calls for $15 billion a year in federal funding to help spark innovation in carbon capture, he said.

McCain would start with about $2 billion in federal research funding that could grow to $20 billion over 5-10 years as a cap-and-trade program starts to generate more revenue, said Woolsey.

Both advisers said they would allow for additional offshore oil drilling, saying that advances in technology had reduce the risks. Congress last month allowed the 25-year-old ban on new offshore drilling to expire.

“There are a lot of drilling rigs and platforms in the Gulf (of Mexico) and that's where the fish congregate. And the spillage even from big hurricanes has been virtually negligible. So I don't see any big reason not to move to the offshore outer continental shelf exploitation,” Woolsey said.

“Drilling there is a reasonable thing. I am not convinced that drilling in ANWR (the Arctic National Wildlife Refuge) is a reasonable thing.”