The Bush administration proposed new fuel economy standards (search) for pickup trucks, minivans and some sport utility vehicles on Tuesday, calling upon automakers to make modest improvements to gas mileage amid rising prices at the pump.

The plan, announced by the Department of Transportation in Atlanta, would require the auto industry to raise standards for most vehicles other than cars beginning in 2008. All automakers would have to comply fully by 2011.

"This is a plan that will save gas and result in less pain at the pump for motorists without sacrificing safety," said Transportation Secretary Norman Y. Mineta (search).

Mineta said the program is expected to save about 10 billion gallons of gasoline.

But the plan does not apply to cars and the largest SUVs, such as the Hummer H2 (search).

It was immediately criticized by environmentalists, who said the proposal would fail to reduce the nation's dependence on imported oil and create new loopholes that would weaken fuel economy requirements. Passenger cars and light trucks, a vehicle category that includes pickups, minivans and SUVs, account for about 40 percent of the nation's oil use.

"At a time when Americans are paying record prices for gas, the Bush administration has sided with its cronies in the auto industry and rejected real solutions," said Dan Becker, director of the Sierra Club's global warming program.

Automakers are currently required to maintain an average of 27.5 miles per gallon for passenger cars and 21 mpg for light trucks. Light trucks are required to meet 22.2 mpg for the 2007 model year.

The proposal would change the method of calculating fuel economy compliance, dividing light trucks into 6 categories based on size, with the smallest vehicles being required to get better gas mileage than larger trucks.

The current system represents an average of manufacturers' entire fleet of light trucks.

At a news conference, Mineta did not unveil complete details of the plan. But he cited one example: minivans currently required to average 21 mpg would be required to get 23.3 mpg by 2011.

Officials referred reporters to the department's Web site, which had not been updated with details late Tuesday morning.

Mineta said the plan represents the first significant change to the Corporate Average Fuel Economy, known in the industry as CAFE, in three decades.

With gas prices soaring this summer to an average of $2.55 a gallon nationally, the new requirements also expect to generate a debate on the nation's dependence on foreign oil.

Jeffrey Runge, administrator of the National Highway Traffic Safety Administration, said that by categorizing vehicles based on size rather than weight, the plan will increase highway safety. He said some automakers responded to current standards by making lighter, and less sturdy, vehicles.

The plan replaces "an old system that conserved fuel but also resulted in more deaths on our highways," he said.