It was a remarkable turnabout. In September, after Hurricanes Katrina and Rita pushed gasoline prices to more than $3 a gallon, President George W. Bush spoke out for energy conservation. The president, who had previously insisted that new oil wells and refineries were the solution to the nation's energy woes, called on Americans to save gas by driving less. Listeners with long memories recalled President Jimmy Carter's television appearances during the oil crisis of the 1970s, when he urged Americans to turn down their thermostats. The only thing missing was the cozy cardigan that Carter had worn when he made his plea.

Environmentalists, though, were less than thrilled by the Bush administration's new strategy, which focused on public-service advertisements encouraging conservation. When it comes to transportation, which consumes 70 percent of U.S. oil and generates a third of the nation's carbon emissions, voluntary measures may be ineffective. Decades of suburban sprawl and neglect of public transit have made it harder for Americans to cut back on driving; from 1990 to 2001, the average length of a shopping trip grew from five to seven miles, and the number of shopping trips per household rose from 341 to 496 a year. Driving to schools, churches, doctors and vacation spots also increased significantly.

A more constructive approach would be to improve the fuel efficiency of cars and trucks. The rise in gas prices has prompted some movement in this direction: after the hurricanes disrupted the oil industry, car buyers shunned gas-guzzling SUVs and snapped up more efficient models. This trend, however, may prove short-lived if gas prices subside as oil companies rebuild their facilities. For this reason, some economists recommend raising the federal gas tax by 50 cents a gallon. The increase could be gradually imposed as prices at the pump decline, so that the impact on consumers is minimized. To offset the disproportionate burden on working-class drivers, revenues from the gas tax could be used to reduce payroll taxes.

Unfortunately, Bush and Congress are adamantly opposed to any new tax, even one that would protect the environment, lessen our dependence on oil from the Middle East and save consumers money in the long run. Instead the Bush administration has proposed revising the corporate average fuel economy (CAFE) standards for light trucks, a category that includes SUVs, pickup trucks and minivans. Whereas passenger cars must average 27.5 miles per gallon, the required average for light trucks is now 21 mpg and scheduled to rise to 22.2 mpg by the 2007 model year. The administration's proposal divides light trucks into six subcategories; although small SUVs have to average 28.4 mpg by 2011, the target for big pickups is only 21.3 mpg. The average for all light trucks would rise to 24 mpg, just 8 percent more than what the current CAFE rules would require by then.

Such feeble measures will do little to ease America's addiction to foreign oil or slow the global warming caused by vehicle exhaust. Lawmakers should press for more stringent CAFE standards that would boost fuel economy for both cars and light trucks by at least 40 percent over the next decade. The goal is technologically feasible--by adopting hybrid engines and strong but lightweight auto bodies, manufacturers can make their vehicles more efficient without compromising passenger safety or inflating sticker prices. What we need are political leaders genuinely committed to energy conservation, not just to speeches and public-service ads.