WASHINGTON — The Trump administration took a major step toward dramatically weakening an Obama-era rule designed to cut pollution from vehicle tailpipes, setting the stage for a legal clash with California that could potentially split the nation’s auto market in two.

The Environmental Protection Agency on Thursday submitted its proposal to roll back climate change rules that required automakers to nearly double the fuel economy of passenger vehicles to an average of more than 50 miles per gallon by 2025. The rules, which would have significantly lowered the nation’s greenhouse gas emissions, were opposed by automakers who said they were overly burdensome.



However, the proposed Trump rule could lead to unintended and unwanted consequences for those same car companies. The Obama-era regulations would have forced automakers to make and sell far more electric and hybrid vehicles, but the new proposal could end up leading to two separate sets of fuel economy regulations within the United States, creating what automakers say would be an even greater regulatory burden.

Jahan Wilcox, a spokesman for the E.P.A., confirmed on Thursday that the agency had sent its proposed regulatory rollback to the White House Office of Management and Budget for review. Typically that is the final step before a proposed rule is published in the Federal Register. The rules are then open for public comment before taking effect, during which the terms could still be modified.