"India wants a deal at Copenhagen. And India is prepared to be an active player in working towards an agreement ... It is in our interests ... because we are very climate-vulnerable,'' says Environment Minister Jairam Ramesh.

China's ambition to grow quickly but cleanly soon may vault it to "front-runner'' status, far ahead of the United States, in taking on global warming, the U.N. climate chief said Monday.

China could steal the show by unveiling new plans on Tuesday at a U.N. climate summit of 100 world leaders. India has also signalled that it wants to be an "active player'' on climate change.

"China and India have announced very ambitious national climate change plans. In the case of China, so ambitious that it could well become the front-runner in the fight to address climate change,'' U.N. climate chief Yvo de Boer told The Associated Press Monday.

"The big question mark is the U.S.''

The development would mark a dramatic turnabout. The United States, under former President George W. Bush's administration, long cited inaction by China and India as the reason for rejecting mandatory cuts in greenhouse gases.

Tuesday's meeting is intended to rally momentum for crafting a new global climate pact at Copenhagen, Denmark, in December. Bush rejected the 1997 Kyoto Protocol for cutting global emissions of warming gases based on its impact on the U.S. economy and exclusion of major developing nations like China and India, both major polluters.

Su Wei, director of China's climate change department, pledged a "pro-active'' approach to make Copenhagen a success. "China takes the threat of climate change very seriously and fully recognizes the urgency to take actions,'' he said, flanked by top climate negotiators from the U.S., India and Denmark at a news conference on Monday. ``China will continue to play certainly an active and constructive role.''

Jairam Ramesh, India's Environment Minister, said India was also committed to reaching a global climate accord.

"India wants a deal at Copenhagen. And India is prepared to be an active player in working towards an agreement ... It is in our interests ... because we are very climate-vulnerable,'' Mr Ramesh said.

Todd Stern, the top U.S. climate envoy, said the Obama administration also is moving ``full speed ahead'' toward helping craft a deal.

But with Congress moving slowly on a measure to curb emissions, the United States could soon find itself with little influence when 120 countries convene in Copenhagen.

China and the U.S. together account for about 40 percent of all the world's emissions of carbon dioxide, methane and other industrial warming gases.

At Tuesday's summit, Chinese President Hu Jintao is expected to lay out new plans that focus on extending China's energy-saving programs rather than committing to a cap on its greenhouse gases, at least not until the fast-growing nation reaches a higher level of development.

Experts say they expect as a first step that China will announce targets for reducing the "intensity'' of its carbon pollution, not shrinking emissions overall, but reducing the carbon dioxide emitted per unit of economic growth.

For the past four years China has been cutting energy intensity and could include a new carbon intensity goal in a five-year plan for development until 2015. China already has said it is seeking to use 15 percent of its energy from renewable sources by 2020.

A key point of dispute remains whether developing countries would agree to be legally bound to a Copenhagen accord. The House of Representatives passed a climate bill this summer that would set the first mandatory limits on greenhouse gases and impose trade penalties on countries that don't cap their emissions. 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.

However, President Barack Obama has opposed attaching trade issues to climate and energy legislation. India has proposed forbidding any government from erecting trade barriers to punish a nation that refused to accept limits on its carbon emissions.

Tuesday's U.N. summit and the G-20 summit in Pittsburgh at the end of this week are intended to add pressure on the United States and other rich nations to commit to cuts and cough up billions of dollars to help developing nations install new technologies and take other actions to adapt to climate change.

Mr Obama has announced a target of returning to 1990 levels of greenhouse emissions by 2020.

The EU is urging other rich countries to match its pledge to cut emissions by 20 percent from 1990 levels by 2020, and has said it would cut up to 30 percent if other rich countries follow suit. European Commission President Jose Manuel Barroso said Monday the Copenhagen meeting could end in deadlock unless all participants agree to sweeping cuts in greenhouse gases.

"The public in Europe would not accept (such cuts) in the EU if the rest of the world does not move too,'' he told the Council on Foreign Relations in New York.

Mr Barroso warned that inaction on climate change would cut the world's gross economic output by 5 percent a year. "We must see that the costs of inaction are higher from an economic point of view than the costs of action,'' he told the Council on Foreign Relations in New York.

British Prime Minister Gordon Brown pledged to attend the Copenhagen talks and called on other heads of state to join him for "a historic moment.'' Environment ministers are scheduled to be the highest-ranking officials there.

"The negotiations are proceeding so slowly that a deal is in grave danger,'' he said in an article published Monday in Newsweek.

"If we miss this opportunity, there will be no second chance sometime in the future, no later way to undo the catastrophic damage to the environment we will cause.''

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