Officials in nine north-eastern US states have reached a ground-breaking preliminary deal to reduce power plant emissions, a US newspaper has reported.
The US produces nearly a quarter of global greenhouse gas emissions
New York is among the states to agree first to freeze power station emissions at current levels, and then cut them by 10% by 2020, the New York Times says.
It follows the Bush administration's decision not to sign up to the Kyoto Protocol on greenhouse gas emissions.
Meanwhile, the White House proposed new rules on fuel efficiency for trucks.
The agreement by the nine states on cutting power plant emissions is thought to be the first of its kind in the US.
Once a final deal is reached, the states involved will have to pass new legislation to bring it into force, considered likely to happen by the New York Times.
The stricter controls could mean higher energy prices in the nine states - but environmentalists hope other states will be encouraged to follow the emissions trading model, the paper says.
THE NINE STATES
Under the initiative, emissions of carbon dioxide from some 600 power stations would be capped at the average emissions level between 2000 and 2004, then reduced by 10% from 2015 to 2020.
Samuel Wolfe, of the New Jersey Department of Environmental protection, told the New York Times that officials "have very high hopes of getting a resolution through to all the [nine] states by the end of September".
The US - the world's biggest emitter of greenhouse gases - declined to ratify Kyoto on the grounds it could harm the country's development or economic growth.
However, the White House announced a surprise pact last month with five Asia-Pacific nations to cut greenhouse gas emissions on terms outside the Kyoto pact.
Rising oil prices have also focused US attention on the need to reduce its dependence on fossil fuels.
Transportation Secretary Norman Mineta said the changes to fuel economy standards, due to begin in 2008, were expected to save about 10 billion gallons of petrol.
"This is a plan that will save gas and result at less pain at the pump for motorists without sacrificing safety," he said.
Larger SUVs like the Hummer will not have to improve fuel efficiency
Under the new guidelines, all US car manufacturers will have to ensure pick-up trucks, minivans and some sport utility vehicles (SUVs) do more miles to the gallon by 2011.
However, the new rules will not apply to the largest SUVs like the Hummer H2, which manages only 10 miles to the gallon.
Passenger cars, which already have to meet a higher fuel economy standard of 27.5 miles to the gallon, are also unaffected.
Environmentalists criticised the plan as failing to do enough to wean the country from its reliance on imported oil, the Associated Press news agency reports.