UNITED NATIONS/LONDON - Official Washington sounded more upbeat on Monday than it has for weeks in sizing up U.S. President Barack Obama's chances of progress on a climate-change bill in Congress this year.

U.S. Senator Barbara Boxer predicted the committee she leads would approve a bill before a U.N. climate summit in Copenhagen in December while Obama's Energy Secretary Steven Chu said he hoped all of Congress would pass a law by then.

Their positive comments contrasted with those of Carol Browner, head of the U.S. Environmental Protection Agency who said 10 days ago she did not expect the U.S. Senate to act in time.

Progress in Congress is viewed as vital to unblocking an impasse on carbon emissions targets and financing at the United Nations-led talks. Leading U.S. lawmakers had forecast it had no chance until next year at the earliest.

Whether there will be a bill on the president's desk and he'll sign it, I'm hopeful it will be, Chu told reporters on the sidelines of a meeting on clean coal technologies in London.

It'll be tight (but) there's a good shot.

OBAMA UNDER PRESSURE

Obama has come under pressure from other countries to show progress, all the more so since he won a Nobel Peace Prize on Friday which cited what it called his more constructive role in meeting the great climatic challenges the world is confronting.

Climate change is competing for attention in Congress with Obama's proposals to bolster a battered economy and overhaul healthcare, which have consumed lawmakers all year.

Senators Boxer and John Kerry, both of Obama's Democratic party, have unveiled legislation that would cut U.S. industry emissions of carbon dioxide and other greenhouse gases by 20 percent below 2005 levels by 2020.

Further boosting Obama's hopes was an opinion piece in The New York Times on Sunday co-written by Kerry and Republican Senator Lindsey Graham, who broke ranks with his party to outline a compromise to limit carbon emissions.

Graham is one of a few dozen fence-sitters who Kerry and Boxer have been courting in order to amass the 60 votes needed for passage in the 100-member Senate. The Kerry-Boxer proposal, opposed by Graham, embraces central elements of a bill passed in June by the Democratic-led House of Representatives.

I believe we will get this bill out of my committee soon, Boxer, who chairs the Senate's Environment and Public Works Committee, told reporters after meeting U.N. Secretary-General Ban Ki-moon at the United Nations on Monday.

Certainly before Copenhagen, and we're hoping maybe to even have it on the floor (of the Senate), she said.

COPENHAGEN MILESTONE  

In a sharp reversal from his predecessor George W. Bush, Obama has vowed to impose mandatory limits on the emission of climate-warming greenhouse gases and made tackling global warming a signature issue of his administration.

The Bush administration had opposed mandatory emission limits, arguing that they would damage the competitiveness of U.S. industry.

Chu would not comment on whether the U.S. could commit to a near-term carbon target in Copenhagen without a bill passed. We're not going to lay out plans B, C and D. It doesn't make any sense. We're going to try make plan A work, he said.

The Copenhagen meeting is meant to seal agreement on a new, tougher pact to extend or replace the existing Kyoto Protocol.

We are confident that a legitimate bipartisan effort can put America back in the lead again and can empower our negotiators to sit down at the table in Copenhagen in December and insist that the rest of the world join us in producing a new international agreement on global warming, Graham and Kerry wrote in the Times piece.

The Kerry-Boxer proposal still faces serious opposition from Republicans -- and from Democrats in states heavily dependent on coal. But Dan Lashof, director of the climate center at environmental group the Natural Resources Defense Council, said the joint Kerry-Graham statement was significant.

It's hard to overstate the significance of this joint declaration. It ensures that the Senate bill will be bipartisan. It demonstrates that there is a pathway to 60 votes to overcome a filibuster, he wrote.

(Additional reporting by Timothy Gardner and Andy Sullivan in Washington; Editing by Howard Goller and David Storey)