WASHINGTON — The Trump administration on Tuesday weakened one of the nation’s most aggressive efforts to combat climate change, releasing new fuel efficiency standards for cars and trucks that handed a victory to the oil and gas industry.

The new rule, from the Environmental Protection Agency and Transportation Department, will almost immediately be plunged into litigation as environmental groups and states with stricter standards, led by California, plan to challenge it.

If the administration’s policy survives those fights, it would spare automakers from having to meet ambitious gas mileage and emissions requirements put in place in 2012 under President Barack Obama. It is among the biggest steps the administration has taken to reverse an existing environmental policy.

The proposal is a dialed-down version of the one the administration originally planned. Instead of proposing zero improvements in fuel efficiency in coming years, it would require automakers to increase fuel economy across their fleets by 1.5 percent a year, with a goal of achieving an average of 40 miles per gallon by 2026. That’s still a major departure from current rules, which mandate annual increases of 5 percent, reaching an average of 54 mpg by 2025.

“We are delivering on President Trump’s promise to correct the current fuel economy and greenhouse gas emissions standards,” EPA Administrator Andrew Wheeler said in a statement. The administration’s plan, he said, “strikes the right regulatory balance that protects our environment and sets reasonable targets for the auto industry.”