The Trump administration is expected to launch an effort in coming days to weaken greenhouse gas emissions and fuel economy standards for automobiles, handing a victory to car manufacturers and giving them ammunition to potentially roll back standards worldwide.

The move — which undercuts one of President Barack Obama's signature efforts to fight climate change — would also propel the Trump administration toward a courtroom clash with California, which has vowed to stick with the stricter rules even if Washington rolls back federal standards. That fight could end up creating one set of rules for cars sold in California and the 12 states that follow its lead, and weaker rules for the rest of the states, in effect splitting the nation into two markets.

Scott Pruitt, the head of the Environmental Protection Agency, is expected to frame the initiative as eliminating a regulatory burden on automakers that will result in more affordable trucks, vans and SUVs for buyers, according to people familiar with the plan.

An EPA spokeswoman confirmed that Pruitt had sent a draft of the 16-page plan to the White House for approval.

The particulars of the plan are still being worked out. Those specifics, which are expected this year, could substantially roll back the Obama-era standards, according to two people familiar with the deliberations.

"This is certainly a big deal," said Robert Stavins, director of the Harvard environmental economics program. "The result will be more gas-guzzling vehicles on the road, greater total gasoline consumption, and a significant increase in carbon dioxide emissions."

According to two people familiar with the EPA's plans, Pruitt was scheduled to formally announce his proposal Tuesday at an auto dealership in the Virginia suburbs, but the schedule remained in flux.

Major automakers would welcome the change. They are prepared to participate in making new rules that meet "our customers' needs for affordable, safe, clean and fuel-efficient transportation," said Gloria Bergquist, a spokeswoman for the Alliance of Automobile Manufacturers, which represents many of the world's largest automakers.

In California, state lawyers said they were expecting a fight. The state has a special waiver under the 1970 Clean Air Act empowering it to enforce stronger air pollution standards than those set by the federal government, a holdover from California's history of setting its own air pollution regulations before the federal rules came into force. "We're prepared to do everything we need to defend the process," said Xavier Becerra, the attorney general of California, in an interview.

The California waiver gives the state considerable power to require automakers to stick to stricter standards. Not only is California a huge car market itself, but 12 other states including New York, Massachusetts and Pennsylvania have historically followed its lead. Together they represent more than a third of the domestic auto market.

"We're going to defend first and foremost existing federal greenhouse gas standards," Becerra said. "We're defending them because they're good for the entire nation. No one should think it's easy to undo something that's been not just good for the country, but good for the planet."

Pruitt has signaled that he is ready to take on such a challenge. "California is not the arbiter of these issues," he said in an interview with Bloomberg TV this month.

On Wednesday, a coalition of free-market groups including the Competitive Enterprise Institute urged Pruitt to take California on. "It is time for the EPA to act," the groups said. If the agency did not act quickly, the groups said, "people across the state of California will be facing unrealistic and costly mandates which threaten their basic right to choose."

President Donald Trump has also spoken about rolling back the efficiency rules, known as Corporate Average Fuel Economy, or CAFE. "I'm sure you've all heard the big news that we're going to work on the CAFE standards so you can make cars in America again," Trump said at a Detroit auto research facility in March last year. "We want to be the car capital of the world again. We will be, and it won't be long."

The rules, aimed at cutting tailpipe emissions of carbon dioxide, a major contributor to global warming, were one of the two pillars of Obama's climate change legacy. Put forth in 2012, they would have required automakers to nearly double the average fuel economy of new cars and trucks to 54.5 miles per gallon by 2025.

The rules also would have put the United States, historically a laggard in fuel economy regulations, at the forefront worldwide in the manufacture of electric and highly fuel efficient vehicles.

Less restrictive regulations in the United States could provide an opening for automakers to push for more lenient standards elsewhere as well, leading to the emission of more pollution by cars around the world.

"The concern is that automakers will go around the world basically trying to lobby regulators, saying, look, because the United States has reduced the pace, everywhere else should too," said Anup Bandivadekar, a researcher at the International Council on Clean Transportation, a think tank that focuses on clean car technology and policy. Global carmakers "apply developments in one region to lobby for changes in other regions."

U.S. automakers initially accepted the plan by Obama in 2009 to harmonize what was then a hodgepodge of pollution and efficiency standards set by the EPA, the National Highway Traffic Safety Administration and California. And the automakers were not in much of a position to resist; they had just taken an $80 billion bailout to survive a global economic crisis.

The plan would have spurred automakers to speed their development of highly fuel-efficient vehicles including hybrid and electric cars. But within weeks of Trump's inauguration last year, the chief executives of the nation's Big Three auto companies met with him in the Oval Office to say that the Obama tailpipe standard was too difficult to achieve.

Trump directed the EPA under Pruitt to craft a new, less strict set of standards. The announcement expected on Tuesday would represent the first legal step in the process.