The Obama administration and major auto manufacturers have reached a deal to raise fuel efficiency standards for cars and light trucks between 2017 and 2025, resolving a contentious negotiation over how to cut vehicles’ greenhouse gas emissions.

The agreement would require U.S. vehicle fleets to average 54.5 miles per gallon or 163 grams per mile of carbon dioxide equivalent by 2025, which represents a 50 percent cut in greenhouse gases and a 40 percent reduction in fuel consumption compared with today’s vehicles, according to sources briefed on the matter.

While the proposal falls short of the 62-mpg standard that environmental and public health groups had lobbied for, it represents a significant step in federal curbs on tailpipe pollution.

It would require a 5 percent annual improvement rate for cars between 2017 and 2025. Light trucks would be required to have a 3.5 percent yearly efficiency improvement between 2017 and 2021, rising to 5 percent between 2022 and 2025, according to the sources, who asked not to be named because the details have not been announced publicly.

The compromise would build upon a landmark accord President Obama forged in 2009 with automakers, environmentalists, unions and California officials, who are allowed to set their own vehicle emission standards under the Clean Air Act. California was the first state to regulate greenhouse gas emissions from cars and light trucks. More than a dozen states have since adopted those restrictions, sparking a legal battle between U.S. automakers and California.

The White House press office issued a statement Wednesday saying the president would unveil the details of the program Friday at the Walter E. Washington Convention Center.

“This program, which builds on the historic agreement achieved by this administration for Model Years 2012-2016, will result in significant cost savings for consumers at the pump, dramatically reduce oil consumption, cut pollution and create jobs,” the statement said.

That first-ever national program for vehicle greenhouse gas emissions mandated that by 2016 cars and light trucks must average 31.4 mpg and 250 grams per mile of carbon dioxide equivalent. In 2010, the U.S. car and light-truck fleet averaged 28.3 mpg and 314 grams per mile.

But the battle over the second round of standards was hard fought, with environmentalists, California and union officials pressing for deep cuts and auto manufacturers maintaining that it was hard to predict what fuel efficiency gains would be possible more than a decade from now. When an agreement was in doubt, California had threatened to set its own, stricter fuel efficiency requirement.

Stanley Young, spokesman for the California Air Resources Board, wrote in an e-mail Wednesday, “We anticipate that the agreement will provide strong standards that benefit the nation and recognize and build on California’s leadership role in air quality and climate protection.”

The White House originally pushed for a 56.2-mpg standard, but automakers demanded a carve-out for pickup trucks, which continue to rank among their top annual sellers. That provision lowered the average fuel efficiency gains to 54.5 mpg and won the support of Chrysler, Ford, General Motors, Honda and Hyundai.

While declining to talk about the details of the agreement, GM’s Washington spokesman Greg Martin said in an interview that he was pleased the two sides were able to reach a consensus.

“The talks over the last few weeks have yielded real progress, and we’re hopeful there’s a way to improve fuel economy but retain customer choice and the industry’s recent resurgence,” Martin said.

Environmentalists, by contrast, said they would withhold judgment for the moment on whether the agreement would deliver sufficient reductions in greenhouse gas emissions and oil consumption.

“Until the White House provides us the full details, we are not in position to assess whether this is a strong proposal or whether there are any significant flaws,” said Roland Hwang, transportation program director for the Natural Resources Defense Council. “From what we’ve read, there are certainly aspects that are encouraging but there are potential loopholes which could be troubling. Now it appears there is an agreement, it’s time for the auto industry to work in good faith to not exploit the loopholes that threaten to undermine the consumer and pollution benefits.”

Michelle Robinson, director of the Union of Concerned Scientists’ Clean Vehicles program, said, “The Union of Concerned Scientists considers this a positive milestone on the road to strong vehicle and fuel efficiency standards and the pollution reductions, energy security benefits and consumer savings they can deliver.

“There are still important details that need to be finalized that will determine the overall success of this program. . . . We anticipate that as this program is implemented and consumers get behind the wheel of more and more clean, fuel efficient vehicles, it will be clear that we can go even farther.”

The White House agreed to provide credits for hybrid pickup trucks and for technologies that are not accounted for in testing that determines compliance with federal standards, such as louvered grilles, solar roof cells and thermoelectric waste exhaust.

The deal also includes a midterm review by the spring of 2018 that will address whether standards for 2022 to 2025 are on track. The assessment will be conducted by the Environmental Protection Agency, the National Highway Safety Transportation Administration and the California Air Resources Board, after which the EPA will determine if any changes are needed.