Todd Stern, the State Department's special envoy for climate change, told a House panel that it was critical for the Senate to pass legislation to give the U.S. the "credibility and leverage" that it needs to convince other countries to reduce their pollution.

While Stern cited progress, he said there's still a divide between developing countries worried that emissions limits will hinder economic growth, and developed countries, which know that global warming cannot be slowed without the participation of fast-growing economies like China and India.

"Nothing the United States can do is more important for the international negotiation process than passing robust, comprehensive clean energy legislation as soon as possible," Stern said.

The House passed a bill this summer that would set the first mandatory limits on greenhouse gases. Factories, power plants and other sources would be required to cut emissions by about 80 percent by 2050.

But action in the Senate has been delayed as lawmakers wrestle with overhauling the health care system.

With three months remaining before 180 nations meet in Copenhagen, Denmark to hammer out a successor to the 1997 Kyoto Protocol, it is looking increasingly unlikely that the Senate will pass a bill in time.

Without one, the U.S. will be hard-pressed to explain to the world how it plans to meet any targets that are agreed to.

Developing countries will also be reluctant to join a treaty without firm commitments by the United States, which until recently, was the largest emitter of greenhouse gases.

The United States rejected the Kyoto Protocol because it exempted countries like India and China from any obligations. The Obama administration has made clear that any new pact should require developing countries to cut emissions.
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