The Bush administration yesterday endorsed a proposal for a small increase in fuel economy standards for light trucks, increasing the mileage requirement for such vehicles by 1.5 miles per gallon over three years.

The decision endorses a recommendation made to the White House last month by the National Highway Traffic Safety Administration. The requirement, covering sport-utility vehicles, minivans and pickup trucks, will begin with the 2005 model year and increase the average standard for such trucks to 22.2 miles per gallon in the 2007 model year. Democrats and environmentalists criticized the increase as too small, while Transportation Secretary Norman Y. Mineta, who oversees NHTSA, said it will save 2.5 billion gallons of gasoline.

The standards, known as corporate average fuel economy or CAFE, have not been raised since 1996. The average standard for other passenger cars is 27.5 miles per gallon across a manufacturer's product line. The change will take effect after a 60-day comment period.

Sen. John F. Kerry (Mass.), an aspiring Democratic presidential candidate, yesterday called the administration's decision "an insult" and "a sham" and said it would save "less than 3 percent of the oil we already import from Iraq." Kerry and Sen. John McCain (R-Ariz.) had proposed increasing overall standards to 35 mpg by 2015, but the legislation was opposed by the Bush administration and defeated.

"Automakers have the technology to do much more than the administration's proposal asks, and much stronger action is urgently needed," said Kevin Mills, director of Environmental Defense's Pollution Prevention Alliance.

Congress established the CAFE targets for cars and trucks in 1975 in response to the Arab oil embargo. But the auto industry has increasingly resisted the CAFE system because of consumer demand for larger, more powerful vehicles that generate huge profits for the industry.

The Alliance of Automobile Manufacturers said yesterday that "this proposal represents a significant challenge." The group warned that fuel-efficient vehicles "do not always meet consumer demand."

Congress has routinely imposed a freeze on CAFE rulemaking. But at the behest of the Bush administration, Congress late last year lifted the freeze, enabling the National Highway Traffic Safety Administration to develop the latest proposal.

A senior administration official said the increase was part of a more comprehensive approach to innovation in transportation technology. Other components of the strategy include research and development, tax incentives and infrastructure planning for a hydrogen-based transportation system.

The official said the administration will also continue to advocate legislative reforms of the CAFE program as outlined in a recent National Academy of Sciences report, especially a market-based, credit trading system coupled with weight- or size-based CAFE standards.

Paul R. Portney, a senior fellow at the Resources for the Future think tank who headed the National Academy of Sciences study, said that while the proposed increase in the mileage standard may seem small to some, it is "an aggressive move" because it will force auto manufacturers and their suppliers to make significant changes in engine designs for the next three model years with little lead time.