The Big Three US automakers have been lobbying to get Washington to focus its energy policy on increased use of alternative fuels like ethanol and pledged last summer to double their production of alternative-fuel vehicles by 2010.

They were rewarded Tuesday when the White House said expanded use of alternative fuels will account for the bulk of its targeted reductions.

But Bush has also called for a five percent improvement in overall fuel economy, a move that could require heavy investments in research and development and threaten popular but gasoline-guzzling vehicles like General Motor's Hummer.

"We plan to work with the White House and Congress to make sure any changes are technically feasible and don't penalize full-line manufacturers like GM," General Motors spokesman Tom Wilkinson told AFP.

Detroit's automakers have long fought the Corporate Average Fuel Economy program which requires automakers to ensure that their fleet of passenger cars average no less than 27.5 miles to the gallon while their fleet of trucks (and truck-based sports utility vehicles) average no less than 22.2 miles per gallon.

The program gives credits to automakers who beat the standard and imposes fines on those who exceed it. Japanese automakers have accumulated massive credits because they have only recently begun offering full-sized trucks and their fleets have traditionally been smaller and more fuel-efficient than those of GM, Ford and DaimlerChrysler.

GM vice-chairman Bob Lutz recently said that tightening CAFE standards "effectively hands the truck and SUV market over to the imports, particularly the Japanese," and compared forcing automakers to sell smaller cars to improve fuel economy with "fighting the nation's obesity problem by forcing clothing manufacturers to sell garments in only small sizes."

A White House fact sheet said Bush plans to tighten fuel economy standards by an average of four percent a year beginning in 2010 for cars and 2012 for trucks.

He also plans to make the system more "flexible" by allowing automakers to buy and sell fuel-economy credits and applying different standards to different categories of vehicles.

DaimlerChrysler spokesman Max Gates said the automaker was working with the government to "develop reasonable, technologically-feasible fuel economy standards."

He said one good alternative was diesel, which improves fuel economy by 20 to 40 percent and reduces greenhouse gas emissions by up to 20 percent.

"We have been a leader in promoting use of clean renewable biodiesel in our diesel vehicles," Gates said. "We are actively working with industry partners for a national standard for b20 fuel (20 percent biodiesel) to increase the use of this fuel."

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