Dec. 3 (Bloomberg) -- The U.S., the only developed nation to reject the emissions-limiting Kyoto treaty, will be ``very open and flexible'' in assembling a new climate accord, its chief negotiator said, refusing to rule out caps on greenhouse gases.

``We don't want to start off with anything here in the beginning of the process that will prejudge what might be concluded in 2009,'' U.S. senior negotiator Harlan Watson told reporters on the Indonesian island of Bali. Delegates from 187 nations are meeting on Bali to discuss a successor to the existing Kyoto Protocol, which expires in 2012.

Such talk has some longtime critics of President George W. Bush's climate policies hopeful that the administration could still reverse course. Australia's new prime minister, Kevin Rudd, ratified the Kyoto treaty earlier today after being sworn into office. The move makes the U.S. the only industrialized country not participating in the climate accord.

``The White House has come a long way in the last few months,'' says economist Jeffrey Sachs, director of the Earth Institute at Columbia University in New York and a special adviser to the UN.

The Kyoto Protocol binds 36 nations to cut the gases by a combined 5.2 percent from 1990 levels by 2012. President Bush walked away from Kyoto in 2001 without offering an alternative.

Bush argued that a mandatory cap on greenhouse-gas emissions would devastate the economy. The president and lawmakers at the time also opposed the treaty on the grounds that China and other developing countries weren't required to reduce emissions. The U.S. and China are the world's largest emitters of global-warming pollution.

Pressure on U.S.

The UN, world leaders including German Chancellor Angela Merkel, and an increasing number of U.S. companies and lawmakers - including many Republicans - have called for Bush and Congress to establish a national emissions limit.

``The political landscape in the U.S. is shifting dramatically'' toward mandatory caps, Alden Meyer, director of strategy at the Union of Concerned Scientists, a nonprofit advocacy group based in Cambridge, Massachusetts.

Bush administration officials last week reiterated their preference for voluntary caps, saying nations should be free to determine their own emission curbs through about 2025.

To contact the reporter on this story: Kim Chipman in Denpasar, Indonesia, at kchipman@bloomberg.net

Last Updated: December 3, 2007 06:17 EST