"Unless the United States decides it wants to be a major and committed leadership player in this and make very specific leadership commitments, much of the rest of the world is going to effectively hide behind the skirts of the United States and not do anything," said Tim Wirth, head of the nonprofit UN Foundation.

"So 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 I believe on the fate of the Earth."

Only the United States and the chief UN climate change representative, Yvo de Boer, are scheduled to make public comments at the Washington meeting.

The White House would not release the names of participants, so it was unclear whether top government officials would attend. At least one country, Brazil, did not plan to send its president or even its environment minister.

In between the UN and Washington meetings, the nongovernmental Clinton Global Initiative will convene in New York from Wednesday through Friday. A nonpartisan project of former US President Bill Clinton's foundation, it will discuss climate change with participants from business, academia, entertainment and nongovernmental environmental organizations.