United Nations — "Arnie" and "Al," Republican and Democrat, shared the world spotlight to press for climate action, adding a touch of star quality to the staid proceedings of a U.N. summit.

The two headliners, California Gov. Arnold Schwarzenegger and former Vice President Al Gore, also highlighted by their presence President Bush's absence from the eight hours of high-level speechmaking Monday on what to do about global warming.

Bush, who did take part later in a small, private U.N. dinner with key players on climate, rejects the idea of international treaty obligations to reduce emissions of carbon dioxide and other "greenhouse gases" blamed for global warming — an idea central to U.N. climate negotiations.

The Republican Schwarzenegger, on the other hand, has taken the lead on emissions caps at the state level, signing legislation mandating such reductions in California.

"One responsibility we all have is action. Action, action, action," the former Hollywood action star said as he helped open the summit, winning warm applause from the assembled presidents and premiers.

The Democrat Gore — a Hollywood figure himself as the lead in the Oscar-winning climate documentary "An Inconvenient Truth" — took his star turn at a summit luncheon, where he cited a lengthening list of global warming's impacts, from the shrinking Arctic ice cap to disappearing lakes in Africa.

"The need to act is now," Gore told delegates to the one-day summit, which drew more than 80 world leaders. "We need a mandate at Bali."

He was referring the annual U.N. climate treaty conference, scheduled for December in Bali, Indonesia, where the Europeans and others hope to initiate talks for an emissions-reduction agreement to succeed the Kyoto Protocol in 2012.

The 175-nation Kyoto pact, which the U.S. rejects, requires 36 industrial nations to reduce the heat-trapping gases emitted by power plants and other industrial, agricultural and transportation sources. The 1997 agreement set relatively small target reductions averaging 5 percent below 1990 levels by 2012.

The advocates of emissions caps say a breakthrough is needed at Bali to ensure an uninterrupted transition from the Kyoto deal to a new, deeper-cutting regime, something that almost certainly would require a change in the position of the U.S., long the world's biggest emitter of greenhouse gases.

Bush objects that Kyoto-style mandates would damage the U.S. economy and says they should be imposed on fast-growing poorer countries such as China and India in addition to developed nations. He instead is urging industry to cut emissions voluntarily and is emphasizing research on clean-energy technology as one answer.

On Thursday and Friday, Bush will host his own Washington climate meeting, limited to 16 "major emitter" countries, including China and India, the first in a series of U.S.-led gatherings expected to focus on those themes.

"The Washington meeting is a distraction," Hans Verolme, climate campaigner for the Worldwide Fund for Nature, told reporters here. The Bush administration needs "to show they are serious and implement domestic legislation to reduce emissions," he said.

Secretary of State Condoleezza Rice, speaking at the summit, put the Washington meetings in a different light, describing them as designed "to support and help advance the ongoing U.N. discussion."

Chinese Foreign Ministry spokesman Jiang Yu said Tuesday that Xie Zhenghua, the vice director of the National Development and Reform Commission, will represent China at the meeting. "We wish the meeting success in promoting better cooperation between major economic entities ... to press ahead on the track of the U.N. (Framework Convention on Climate Change) and the Kyoto Protocol," Jiang said at a briefing.

Late Monday, U.N. Secretary-General Ban Ki-moon was asked by reporters about Bush's position during the informal dinner discussions. "He made it quite clear that what he's going to do is help the United Nations' effort," he replied. On Tuesday, Brazil's president, Luiz Inacio Lula da Silva, emerged from a bilateral meeting with Bush saying the U.S. president told him he was ready to be more flexible on climate.

Japan's envoy, former Prime Minister Yoshiro Mori, told the summit Tokyo believes the separate U.S. talks will "contribute to achieving consensus" in the U.N. process, in which all agree that China, India and others must eventually accept emission limits.

But Japan, the Europeans and others, to one degree or another, stressed that all nations — including the United States — must accept binding emissions targets, something Bush gives no sign of doing.

To try to spur global negotiations, the European Union, which must reduce emissions by 8 percent under Kyoto, has committed unilaterally to a further reduction of at least 20 percent by 2020.

Speaking for the EU, French President Nicolas Sarkozy told Monday's gathering that "all the developed countries and the largest emitters" must commit to a 50 percent reduction by 2050. In a comment clearly aimed at Washington, he also said the U.N. negotiations are the only "legitimate framework," a point stressed repeatedly by Ban as well.