DETROIT — The Bush administration is considering changes to fuel economy regulations that would encourage manufacturers to offer more large cars, station wagons and smaller sport utility vehicles that are built more like cars.
The idea behind the changes is that such vehicles are safer than both small cars and sport utility vehicles and pickups, and that if more people drove them, fewer people would die in crashes. Producing more such vehicles and fewer very small or very large vehicles would reduce the increasing disparity among American vehicles, both in weight and how high they ride.
Because they ride so high, sport utility vehicles and pickups pose more dangers to drivers of small cars than large cars do. They are also more dangerous for their own occupants because of their increased rollover risk.
But the idea is opposed by environmentalists and has already drawn a sharply worded protest from the United Auto Workers union. Both are concerned, for different reasons, that the Big Three will stop making small cars because they lose money making them and will no longer be compelled to.
For the last several months, representatives of the Department of Energy, the National Highway Traffic Safety Administration, the Environmental Protection Agency and several other federal agencies have been exploring changes to the way fuel economy is regulated.
Under the current system, in effect since the 1970s, automakers must meet one average for their fleets of cars (currently 27.5 miles per gallon) and a much lower average (20.7 miles per gallon) for their light trucks, which include sport utility vehicles, pickups and minivans.
To reach those averages, automakers generally build small vehicles with higher fuel economy to offset large, less fuel-efficient vehicles.
The change being considered by the Bush administration will not be described for a month or two, in an initial proposal for fuel economy in the 2008 model year and beyond. But the type of system being considered could eliminate the distinction between cars and light trucks and instead base fuel economy requirements on the weight or size of vehicles.
So automakers would no longer have to build small cars to help reach the average required of all cars. As for the largest sport utilities and pickups, the fuel economy standard could in theory be raised enough to force the automakers to make such vehicles smaller. As a result, fewer vehicles on the road would be either very big or very small.
"Large passenger cars and minivans are the safest way to move around large numbers of people," said Dr. Jeffrey W. Runge, the Bush administration's top auto safety regulator, at a conference in January. "And yet," he added, referring to the current system known as Corporate Average Fuel Economy standards (CAFE), "we have CAFE-ed large cars out of existence."
"We need a quantum leap in fuel economy without sacrificing safety," he added.