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WASHINGTON — Regulators have sent the White House a proposal seeking to scale back Obama-era rules to combat climate change through tougher fuel-economy standards for cars and trucks.

The Environmental Protection Agency and National Highway Traffic Safety Administration delivered the proposals to the Office of Management and Budget for review, one of the required steps before a federal rule is adopted.

Landmark rules by the Obama administration mandated that cars and light trucks average more than 50 miles per gallon, equivalent to 36 miles per gallon in real-world driving conditions, by 2025. The move was meant to fight climate-changing emissions from car and truck exhaust. California, which has a federal waiver that allows the state to set its own fuel-economy standards, agreed to that proposal, and automakers currently follow the same mileage requirement nationally.

Transportation is the largest source of climate-changing greenhouse-gas pollution in the United States, and the biggest share of that comes from cars and trucks, according to data from the U.S. Energy Information Administration and the EPA.

EPA administrator Scott Pruitt earlier signaled plans for a rollback in the Obama fuel-economy standards, saying this spring the standards were "too high." President Donald Trump declared in January his administration was cutting rules on Detroit automakers and would "get Motor City revving its engines again."

A draft of the Trump administration changes made public earlier this spring would lower the requirements for automakers, freezing them at a minimum mileage of roughly 30 miles per gallon in real-world driving from 2020 through at least 2025.

The draft proposal includes that option and others, including leaving the Obama rules unchanged, for a final decision by the White House, according to a person familiar with the proposal. Trump has targeted a series of Obama administration measures for rollbacks and elimination, calling them a drag on U.S. businesses and jobs.

The plan, expected to be made public by mid-June, also makes the case for mandating a single national standard that would prevent California from setting its own fuel-efficiency requirements, said the person, who was not authorized to speak publicly about the plan and spoke on condition of anonymity.

Any big change in the standards by the Trump administration would bring lawsuits from environmental groups and California, as well as the dozen states that follow California's fuel standards. The states jointly account for about 40 percent of sales of new vehicles in the United States.

A rollback in U.S. fuel-economy efforts also would affect the automobile industry globally, and weaken efforts against smog and other pollutants.

EPA spokesman Jahan Wilcox said Thursday the agency would not comment while the proposals go through federal review.

Pruitt said in April that regulators would establish a standard that "allows auto manufacturers to make cars that people both want and can afford — while still expanding environmental and safety benefits of newer cars."

An environmental group framed the case for keeping tougher standards as a pocketbook argument as well.

"With gas prices on the rise, rolling back fuel-efficient standards that save drivers money on gas is a terrible idea," David Doniger, climate-program director at the Natural Resources Defense Council, said in a statement. "Forcing people to pay more to fill their tanks makes no sense."