By Deborah Zabarenko, Environment Correspondent

UNITED NATIONS (Reuters) - U.N. Secretary-General Ban Ki-moon and California Gov. Arnold Schwarzenegger had the same message on Monday at a special session on climate change, urging quick action to stem emissions that heat the planet.

"Today let the world know that you are ready to shoulder this responsibility and that you will address this challenge head on," Ban told some 80 world leaders at the session's opening.

"The time has come to stop looking back at the Kyoto Protocol," Schwarzenegger said. "It is time to stop looking back in blame or suspicion ... The rich nations and the poor nations have different responsibilities, but one responsibility we all have is action."

Ban wants the one-day gathering to send a "strong political message" about the urgency of the problem of curbing the greenhouse gas emissions that contribute to climate change.

It is the first of three U.S. events on climate change this week that are likely to focus attention on whether Washington can make good on its pledge to take a leading role in curbing such emissions.

But it is not a negotiating session. That will come in December in Bali, Indonesia, where climate experts will try to craft a successor to the emissions-limiting Kyoto Protocol, which expires in 2012.

Al Gore, the former presidential candidate and star of the Oscar-winning global warming documentary, "An Inconvenient Truth," is also to address the U.N. meeting.

But President George W. Bush, who defeated Gore, will not speak at this gathering, but he will dine with Ban after it ends.

Bush has rejected the Kyoto Protocol, an international agreement that requires 36 industrial nations to cut greenhouse emissions by at least 5 percent from 1990 levels by 2012.

He contends the accord unfairly burdens rich countries while exempting developing countries like China and India and that it will cost U.S. jobs.

Developing countries have said it is unfair to ask them to curb their emissions as their economies grow while industrialized nations have been polluting for decades.

Bush does plan to speak at a two-day Washington meeting at the State Department on Thursday and Friday, a gathering of "major economies" -- the world's biggest global warming contributors -- on energy security and climate change.

A third conference, the nongovernmental Clinton Global Initiative, will convene in New York from Wednesday through Friday to discuss climate change with participants from business, academia, entertainment and environmental organizations.

(Additional reporting by Jeff Mason)