Most leaders of the world's governments will attend. U.S. Secretary of State Condoleeza Rice will represent American interests at the meeting. President Bush will meet with the leaders of the UN and other governments at a dinner tonight.

The United States is the largest emitter of greenhouse gases in the world. But the U.S. has declined to sign a U.N. climate document, the Kyoto Protocol, ratified by most of the world's leading nations in 1997. The protocol expires in 2012.

Those close to the scene are looking for a change in U.S. policy based on a series of reports released this year by a worldwide panel of scientists concluding that the scientific proof for climate change is "unequivocal."

"What the United States does, and how the United States decides to enter this negotiation is going to be a very, very telling commentary on the future of the climate negotiations, and ultimately, I believe, on the fate of the earth," said Tim Wirth, president of the U.N. Foundation and a former U.S. Senator from Colorado. Wirth represented the Clinton Administration during U.N. climate negotiations in 1995.

At a news conference last week sponsored by the National Environmental Trust, Sen. John Kerry (D-Mass.) was hopeful about the meeting.

"I'd like to see the President of the United States take the lead and say the United States of America is going to set fixed targets, that we're going to lead the world in alternative renewable fuels and technologies, and we're going to help contribute to the technical assistance and the technologies, themselves, to less developed countries in an effort to facilitate their economic transformation," Kerry said.