"With this in mind, I have urged the Bush administration and my colleagues in Congress to return to a leadership role on the issue of climate change," Lugar said.

He said the United States "must be open to multilateral forums that attempt to achieve global solutions to the problem of greenhouse gases."

The European Union, Japan and much of the rest of the industrial world are imposing mandatory cuts on emissions linked to global warming in the Kyoto treaty on global warming. The Bush administration favors asking US companies to join a voluntary emission reduction program.

Lugar, as well as fellow Republican Sens. Norm Coleman of Minnesota and George Voinovich of Ohio, stressed that China and India, which are spewing out more greenhouse gases than anticipated, needed to be brought into the UN's 1992 Kyoto Protocol, where developing nations had received exemptions.

"The issue is alive," Voinovich told reporters. "We are concerned about it. I think the more we work together on it, the more likely it will be that we will do something about reducing greenhouse gases."

Coleman said that "the issue of renewables is not just a Midwest area issue anymore" but a national issue "so we have to lessen our dependence on Middle East oil, that's a reality."

"The dynamic has changed regarding global warming," he said. "Clearly the massive consumption (of India and China) opens an opportunity for additional discussion."

Lugar, a Republican from the corn-growing state of Indiana, said breakthroughs in genetic engineering made it possible to break down a wide range of plants and that ethanol processing remains a relatively young industry.

"Oil processing has had the comparative benefit of a century of intensive research and development," he said.

In November, Lugar and Sen. Joe Biden, a Delaware Democratic, introduced a Senate resolution calling for the United States to return to negotiations on climate change.

In 2001 President George W Bush pulled out of the UN's Kyoto Protocol, which seeks to cut rich nations' emissions of heat-trapping gases from burning fossil fuels. Bush said Kyoto would harm the US economy and that it wrongly excluded poor nations from first targets to 2012.