"That's a very significant and encouraging step," Independent Senator Joe Lieberman said of Chinese President Hu Jintao's offer to reduce emissions growth by a "notable margin" by 2020 from their 2005 levels.

Lieberman said he hoped "it'll make it a little bit easier for us here as we try to pass climate change legislation," by answering critics who reject US action absent similar reductions by developing economies like China or India.

"There's no question there's a certain number of people here who will not take on some of the responsibility that we have to take on to do things to deal with climate change unless China also does," he told reporters.

At the same time, Democratic Senate Majority Leader Harry Reid sought to counter concerns that the Senate may put off action on the legislation amid a pitched political battle over how to remake US health care.

"We're going to push climate as hard and as fast as we can," said Reid.

The House of Representatives approved its "cap-and-trade" legislation in June, and leading senators are due to unveil their legislation later this month or in early October.

Nations are due to meet in December in Copenhagen to lay the framework for the successor to the landmark Kyoto Protocol, whose obligations on wealthy nations to cut greenhouse gas emissions expire in 2012.

Developed nations, while pledging to fight global warming, have insisted that emerging powers also commit to action as part of Kyoto's successor.

Hu did not put a specific figure on the cuts, but told the UN General Assembly that they would be measured by unit of Gross Domestic Product, in line with China's concerns about preserving its rapid economic growth.

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