WASHINGTON — From the president's visit to a Delaware biofuels lab to top Democrats making nice at the Washington Auto Show, the debate over the future of the U.S. auto industry took center stage yesterday.

President Bush and his aides fanned out to promote the "20 in 10" energy proposal he unveiled Tuesday, with the administration defending it from environmentalists' complaints.

Meanwhile, U.S. Rep. John Dingell, D-Mich., led House Speaker Nancy Pelosi on a brief tour of fuel-efficient Detroit models at the auto show, an event staged to smooth over their dispute about how the House will tackle global warming.

With both branches of government in pursuit of more efficient vehicles, tougher fuel economy rules seem increasingly likely. But with no consensus on how to tackle global warming in other parts of the economy, Detroit automakers will likely carry much of the burden for concerns about the nation's energy security and climate change over the next several months.

Bush's proposal aims to cut U.S. gasoline consumption by 20 percent by 2017 through an increase in fuel economies and a sharp boost in alternative fuels. While the alternative-fuels plan enjoys widespread support from Democrats and Republicans, industry and environmental groups said the fuel economy pitch would face a hard battle between lawmakers who want higher targets and automakers.

"The future of the auto market is going to be driven by upside swings in the price of oil and concerns about global warming," said Joseph Romm, an author and former energy-efficiency official in the Clinton administration. Detroit automakers "need to make fuel-efficient vehicles, and if the government has to require it, that's not so bad."

Federal officials said in order to save about 8.5 billion gallons of gasoline, fuel efficiency standards would have to rise 4 percent a year starting in the 2010 model year for cars and the 2012 model year for trucks.

In a speech at a DuPont research lab in Delaware, Bush said his "20 in 10" plan was essential to reducing the threat posed by foreign regimes that can tinker with the nation's energy supply. Sixty percent of U.S. oil is imported. In addition to the mileage increase, the president's plan would mandate the production of 35 billion gallons of alternative fuels by 2017.

The plans are "all aiming to make us less dependent on oil, and thereby making us more secure nationally and be able to say we're better stewards of the environment," Bush said.

Bush also signed an executive order yesterday directing federal agencies to buy more fuel-efficient vehicles, increase their alternative-fuel consumption by at least 10 percent a year and buy plug-in hybrid vehicles if they become available.

Environmentalists have noted that the 4 percent increase in the president's plan, equal to about 34 miles per gallon, mirrors similar ideas in Congress.

The major difference is that Bush's increase is a goal, not a hard figure — the final increase would be set by federal regulators after reviewing the costs to automakers based on future product plans.