To many Californians, that would mean driving a sub-compact instead of an SUV, he said. "I don't think a lot of soccer moms in Marin County would appreciate that."

Nearly half, 47 percent, of passenger vehicles sold in the nation's most-populous state are SUVs, minivans or light trucks - a percentage that has tripled over the last 30 years.

The proposed law would require the state's Air Resources Board to adopt, by 2005, regulations that would achieve "the maximum feasible reduction" in emissions of greenhouse gases, including carbon dioxide, emitted by cars and light-duty trucks, the category that includes sport utility vehicles.

The bill was introduced by Fran Pavley, a state assembly member representing Woodland Hills, a suburb north of Los Angeles. It was passed by the Assembly and will be heard by the state Senate's appropriations committee on April 29.

If the bill becomes law, the regulations would not take effect until at least Jan. 1, 2006.

Because California's Air Resources Board was established before the U.S. Environmental Protection Agency was formed under the Clean Air Act of 1970, California is unique in its ability to impose air quality standards independent of federal regulation. The state air board already sets strict standards for tailpipe emissions of smog-causing pollutants like nitrogen oxides.

STEPPING IN WHERE BUSH STEPPED OUT

"Because CO2 has not been considered a major pollutant, it has been the purview of the federal government," said Jerry Martin, a spokesman for the state's air board. "But the (Bush) Administration has not endorsed the Kyoto agreement so there are no regulations that specify CO2 levels."

The United States, which emits around one quarter of the world's man-made "greenhouse gases," earlier this year pulled out of the 1997 United Nations anti-pollution treaty signed by President George Bush's predecessor Bill Clinton, saying it would harm the economy and instead came up with a voluntary plan to combat global warming.

The threat of global warming caused carbon dioxide emissions from coal, oil, and gas-fueled energy sources is the subject of much debate with many scientists believing it will cause polar ice caps to melt and climates to change, while others say fluctuations in temperatures are not that unusual.

The California Air Resources Board does not currently have the authority to regulate greenhouse gases, but the state's largest source of them is vehicles, Martin said.

"All autos emit CO2 and other greenhouse gases. SUVs consume more fuel, so they emit more gases," he explained.

Fuel economy is regulated by the federal government, which last month rejected a proposed 50-percent boost in fuel-efficiency for gas-guzzling cars and SUVs. Existing Corporate Average Fuel Economy, or CAFE, standards, require passenger cars to average 27.5 miles per gallon, while SUVs, along with mini-vans and other vehicles in the "light truck" category, need only achieve 20.7 mpg.

"It is silly that Californians would pay the price for a global problem," one auto company representative said. "The bill is too broad and too vague."

The bill's sponsors, however, say global warming presents unique risks for the state including potential reductions in water supplies and a projected doubling of catastrophic wildfires.