The Bush administration proposed higher fuel economy standards for SUVs and minivans yesterday with a new regulatory system that sets different mileage goals for six sizes of vehicles, replacing the current single standard for all light trucks.

Administration officials say the regulations would result in more fuel savings than any previous increase in efficiency standards for larger vehicles. Transportation Secretary Norman Y. Mineta said the rules would save 10 billion gallons of gasoline and "result in less pain at the pump for motorists, without sacrificing safety."

But environmentalists say the complex proposal adds up to little real change and continues to reward Detroit for building bigger vehicles. It also addresses the complaint of U.S. automakers that it's easier for foreign-owned manufacturers to meet existing standards because they sell fewer large trucks.

"The proposal is almost embarrassing in terms of its effect on fuel consumption," said Eric Haxthausen, an economist with Environmental Defense of Washington. He called the 10 billion gallons of fuel savings a "weak yardstick" because it would be spread over as long as 15 years. Last year, for instance, U.S. drivers consumed nearly 140 billion gallons of gas, according to federal Energy Information Administration. "We can and should do better," Haxthausen said.

The measure comes at a time when U.S. drivers are coping with skyrocketing gas prices and often blaming President Bush for their plight. Rep. Thomas M. Davis III (R-Va.) said the Bush administration has made "a huge policy reversal" after blocking efforts in Congress earlier this year to tighten fuel economy standards.

"The administration and the leaders fought this in the energy bill," he said. "I'm happy to see them coming around to it now. Better late than never."

The plan would do away with an industry-wide corporate average fuel efficiency -- or CAFE -- standard for vehicles classified as light trucks, which includes SUVs, pickup trucks, minivans and other models that now make up more than half of all new vehicles sold in the United States. Instead, fuel economy would be calculated for six different segments of these vehicles, from the smallest, such as the Chrysler PT Cruiser and the Toyota Rav4, to the biggest, such as the GM Silverado and Nissan Titan.

Each automaker would also be given an average fuel economy goal for its particular mix of vehicle sales.

Under current standards, automakers must maintain an average of 27.5 miles per gallon for passenger cars and 21 mpg for light trucks. The light-truck standard is already scheduled to rise to 22.2 mpg for the 2007 model year.

The new regulations would start affecting light trucks in the 2008 model year, and all such vehicles would have to comply by 2011 models. For the smallest category of trucks, the final fuel efficiency target would be 28.4 mpg; for the largest SUVs and pickups, it would be 21.3 mpg.

The proposal is submitted for public comment until Nov. 22, and the National Highway Traffic Safety Administration hopes to issue a final rule by next April.

Big American automakers have historically fought tougher fuel standards, saying it is costly to reengineer cars and trucks to comply.

"The higher we go [in fuel economy standards], the more difficult the challenge becomes because there is a lot of safety content that is adding weight to cars, as well as convenience features people want -- so there are a lot of trade-offs that pose challenges for us," said Christopher Preuss, a spokesman for General Motors Corp.

The industry has argued that achieving better fuel efficiency often means producing smaller, lighter cars that are less safe to drive. Yesterday's proposed rule change is aimed at discouraging automakers from building smaller vehicles unless the market demands it. The approach "lessens the incentive to design smaller vehicles to achieve a 'light truck' classification," the rule says, because smaller trucks will be regulated almost as stiffly as passenger cars.

Critics say the rule actually encourages companies to make bigger vehicles that are less fuel efficient.

For example, the Subaru Outback, which is in the smallest class of vehicles, could be made less than an inch wider and longer and move up into the next size grouping, thereby lowering its fuel economy requirement, said David J. Friedman, research director for the clean vehicles program of the Union of Concerned Scientists.

"One of the fundamental problems with the system is automakers can add size, in some cases only a tiny amount, and meet a dramatically lower standard," he said.

Other activists complain that the fuel efficiency increase being sought averages out to less than half a mile per gallon per year, with an average of about 24 mpg slated for 2011 -- a total improvement of 1.8 mpg over four years.

But administration officials defend the new CAFE standards as far-reaching. John D. Graham, administrator of Office of Information and Regulatory Affairs at the Office of Management and Budget, said the new rules would result in a 15.9 percent improvement in light-truck fuel economy from 2004 to 2011. "There is no administration with a better record" on the issue, he said.

Graham pointed out that the smallest SUVs would end up with a fuel requirement of 28.4 mpg, "which is more demanding than the [current] 27.5 miles per gallon for passenger cars."