But criticism of the White House stance is growing, even from the ranks of the Republican majority in Congress, and in a handful of states where critics say US environmental policies are too often shaped by economic concerns.

"There is no serious initiative that the administration has proposed that will come anywhere close to dealing with the soaring US emissions," said Alden Meyer of the Union of Concerned Scientists, an influential professional association.

In his view, the voluntary programs for reduction of emissions set forth by Bush in 2002 are toothless.

But Bush continues to oppose caps on carbon dioxide emissions, largely deemed responsible for the greenhouse effect and global warming.

The United States initially signed up to Kyoto's framework but in one of his first acts after taking office, Bush abandoned the accord in March 2001 on the grounds that it would be too costly for US industry.

Congress, where a majority opposed US participation in the treaty, was compliant.

A bipartisan Senate resolution, unanimously adopted in 1997, said the president should not even sign an accord that forced the United States to reduce greenhouse gas emissions without developing countries, including China, shouldering the same obligations.

The resolution further stipulated that Kyoto -- concluded in December 1997 -- should not be seriously detrimental to the US economy. It was estimated that adhering to the protocol would cost five million US jobs.

But now that the treaty is taking effect, amid spreading evidence of climate change, the debate in the United States is set to intensify, according to Jeff Fiedler of the Natural Resources Defense Council, the environmental lobby group.

"There is a momentum building in the US to deal seriously with climate issue and the widespread recognition that only mandatory emission limits would be effective," Fiedler said.

Several states have already launched initiatives aimed at reducing greenhouse gases, according to a recent study by the Pew Center. The United States is currently responsible for 21 percent of the world's emissions.

The independent research center says 18 states demand that electrical power plants -- many of them powered by burning coal -- produce a part of their electricity with renewable energy sources.

The Pew Center also points to a new trend of regional, as opposed to national, actions to address climate change issues in the United States.

Nine northeastern and Atlantic coast states plan to establish an emissions trading market, modeled on Kyoto, providing financial incentives to cut pollution.

California, the most populous US state, has just adopted legislation, supported by Republican Governor Arnold Schwarzenegger, requiring car makers to sell vehicles that emit less carbon dioxide by 2009, permitting a 30 percent drop in emissions by 2016.

The mood is also changing in Congress, where a group of Republican senators have openly stated their support for federally-imposed limits on carbon dioxide emissions.

Thursday, Republican Senator John McCain and Democrat Joe Lieberman presented draft legislation that would establish caps on 80 percent of polluting emissions in the country.

Republican Senator Chuck Hagel, who opposed Kyoto, called in a speech Thursday for new public and private actions including in developing countries to reduce greenhouse gas emissions.

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