LONDON -- The leaders of Britain and Germany said Friday they would work to put global warming at the top of the international agenda and would try to get the U.S. more involved in confronting the problem.

British Prime Minister Tony Blair and German Chancellor Angela Merkel made the comments during talks about Berlin's 2007 presidencies of the European Union and the Group of Eight industrialized nations.

Asked whether it was possible to reduce emissions of the gases blamed for rising temperatures without the participation of the U.S., the world's biggest polluter, Blair said under Merkel's leadership "there's a real opportunity to make progress next year and certainly we will give every support we can. And I am hopeful that that will be something that all countries can participate in."

He said that in many U.S. states, particularly California, both Republicans and Democrats were ready to act on climate change and noted that President Bush spoke in his State of the Union speech about moving away from dependence on carbon-based fuels.

"I think there are signs of hope here," he said. "There is a real reason for us to promote clean energy."

A report this week by Sir Nicholas Stern, a top British government economist, warned that if the world does not act to halt global warming, it will cause an economic catastrophe on the scale of the Great Depression and the two world wars.

Merkel said during a joint news conference after Friday's talks that she had been very interested in the report. World leaders "have to do everything in order to issue a wake-up call to our populations. Climate change is one of the great challenges of the 21st century," she said.

"Europe has an enormous opportunity on new technologies, assuming a responsible and a leading role for the rest of the world," she said. "We have a very important task here, to persuade our Canadian and American friends that this is a very important issue for all of us."