Senators Joseph Lieberman and John Warner said their plan would focus on 80 percent of greenhouse gas emissions, to cut these by 70 percent below current levels by 2050, and could be used as a blueprint in the fight against global warming.

"We hope it will be a turning point," said Lieberman, who sits as an independent Democrat in the Senate, adding that the plan could reverse US foot dragging on tackling the global threat from climate change.

"We have been slow, we are already late, but not too late," he said.

The proposal, one of several expected to come up in the Senate later this year, lays out a mandatory, market-based cap-and-trade program that would cover 80 percent of US greenhouse gas emissions.

It is designed to cut those emissions back to current levels by 2012, pare them by 10 percent of current levels by 2020, and to reduce them to 70 percent below current levels by 2050.

At the same time, the senators said, their plan, to be the basis of legislation introduced into the Senate later this year, contains "robust" measures to protect American jobs and sustain US economic growth.

It will include the establishment of a Climate Change Credit Corporation to permit industry sectors to buy emissions allowances to regulate the amount of harmful gases they spew into the atmosphere.

Warner, a Republican, said he came late to the issue, after mulling over the potential security implications of global warming.

"In my 28 years in the Senate, I have focused above all on issues of national security, and I see the problem of global climate change as fitting squarely within that focus," he said.

Environmentalists have alleged that since President George W. Bush came to office in 2001 his administration has ignored and even tried to hide looming evidence of global warming and taken little or no action to combat climate change, or the US title as the world's biggest greenhouse gas polluter.

They are also critical of Bush's refusal to ratify the Kyoto protocol on global warming, which he has criticized as excessively flawed and a threat to the US economy.

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