America's oil, gas and coal industry has increased its lobbying budget by 50%, with key players spending $44.5m in the first three months of this year in an intense effort to cut off support for Barack Obama's plan to build a clean energy economy.

The spoiler campaign runs to hundreds of millions of dollars and involves industry front groups, lobbying firms, television, print and radio advertising, and donations to pivotal members of Congress. Its intention is to water down or kill off plans by the Democratic leadership to pass "cap and trade" legislation this year, which would place limits on greenhouse gas emissions.

A defeat for the bill would have global consequences. The international community is depending on America, as the world's biggest per capita polluter, to set out a firm plan for getting off dirty fuels in the months before crucial UN negotiations in Copenhagen in December.

Without such action, the chances of getting a deal that scientists say is vital to limiting dangerous climate change are much reduced.

Those high stakes have intensified the fight for control over America's energy future. "There are an awful lot of people who have an awful lot to gain and lose and they have been acting accordingly," said Evan Tracey, founder of the Campaign Media Analysis Group (CMAG), who has tracked the proliferation of climate change ads.

But it is an unequal contest. Liberal and environmental organisations, as well as the major corporations that support climate change legislation, say they are being vastly outspent by fossil fuel interests.

"These guys are spending a billion dollars this year convincing Americans that they are clean, green, cuddly and warm," said Bob Perkowitz, founder of the eco- America PR firm. Perkowitz is to brief the White House yesterday on a new environmental messaging strategy. "The enviros are getting their message out, but they are being outspent by 10 to one." he said.On advertising, the ratio is about three to one. The oil and coal industry spent $76.1m on ads from 1 January to 27 April, according to CMAG data seen by the Guardian. Environmental groups, led by Al Gore's Alliance for Climate Protection, the Environmental Defence Fund and the Sierra Club, spent $28.6m on ads in the same period, Tracey said.

Despite its global significance, the fate of the draft "cap and trade" bill now lies in the hands of just a dozen Democrats, who have yet to back Obama's energy transformation. The Democratic leadership cannot take their support for granted. Seven of those pivotal Democrats received campaign donations in excess of $100,000 from the oil and gas industry, coal producers, and electricity firms during last year's elections, according to an analysis provided to the Guardian by the Centre for Responsive Politics. Another two received more than $90,000 last year.

Environmentalists say those Democrats, who hold the balance of power on the committee, pose a far greater threat to the chances of passing climate change legislation than a full vote in the House of Representatives. "If they can get that bill through the subcommittee what is going to emerge is a piece of legislation," said Tony Kreindler of the Environmental Defence Fund. "So this is ground zero for the vote."