WASHINGTON — The Obama administration on Tuesday finalized strict new fuel-efficiency vehicle standards Tuesday, requiring the U.S. auto fleet to average 54.5 miles per gallon by 2025, according to individuals briefed on the matter.

The new rules, which expand existing standards requiring American-made cars and light trucks to average 34.5 mpg by 2016, will significantly cut U.S. oil consumption and greenhouse-gas emissions by the time they are fully implemented, the Environmental Protection Agency said. Unlike many energy policies enacted under President Obama, the vehicle standards are a relatively uncontroversial move embraced by industry and environmentalists alike.

Phyllis Cuttino, director of the Pew Clean Energy Program, said that so many people now accept the idea of greater fuel efficiency does not lessen the rules' "historic" importance.

"We've just come a long way in five years," Cuttino said, noting that in 2007 lawmakers debated whether the U.S. fleet could average 30 mpg by 2025. "This gives me hope for energy policy in this country."

This second phase of standards, which apply to model years 2017 to 2025, will double the efficiency of the U.S. fleet compared with vehicles manufactured in 2008.

Tuesday's announcement by Transportation Secretary Ray LaHood and EPA Administrator Lisa Jackson will mark the culmination of a compromise the White House forged between the auto industry, environmentalists, labor unions and the state of California.

California had enacted its own greenhouse-gas emissions standards several years ago and had battled the auto industry in court until the administration brokered a deal between all the parties in May 2009.

While the sales of some electric cars have not taken off as quickly as industry experts predicted, the overall efficiency of the U.S. auto fleet continues to rise as consumers have shifted away from buying trucks to cars. According to industry analysts, U.S. motor-fuel consumption, which had been growing steadily for decades, is on the decline.

In addition to increasing fuel efficiency, the rules establish an emissions standard of 144 grams of carbon dioxide per mile for passenger cars and 203 grams for trucks.

Kevin Kennedy, who directs the U.S. climate initiative at the World Resources Institute, noted that light-duty vehicle emissions represent approximately 17 percent of the country's total greenhouse-gas emissions.

"These rules represent one of the best opportunities for the administration to take a bite out of emissions that are damaging the planet, and in a way that's good for consumers and the auto industry," Kennedy said.

According to EPA estimates, the proposed standards would reduce carbon dioxide emissions by 2 billion metric tons over the lifetimes of light-duty vehicles sold between model years 2017 and 2025. By 2025, EPA said, the standards would cut U.S. oil consumption by 2.2 million barrels of oil per day compared with 2010, save $1.7 trillion in fuel costs and result in an average fuel savings of more than $8,000 per vehicle.

Even as the administration moves to finalize the standards, presumptive GOP presidential nominee Mitt Romney has vowed to overturn them if elected. Last fall, Romney said he "would get the EPA out of its effort to manage carbon dioxide emissions from automobiles and trucks."

In February, Romney reiterated his opposition during a speech in Detroit, saying the fuel-efficiency rules "hurt domestic automakers and provided a benefit to some of the foreign automakers."