FRESNO, Calif. — California officials demanded Monday that the Trump administration back off a plan to weaken national fuel economy standards aimed at reducing car emissions and saving people money at the pump, saying the proposed rollback would damage people’s health and speed climate change.

Looming over the administration’s proposal is the possibility that the state, which has become a key leader on climate change as Trump has moved to dismantle Obama-era environmental rules, could set its own separate fuel standard that could roil the auto industry. That’s a change the federal government is trying to block.

“California will take whatever actions are needed to protect our people and follow the law,” Mary Nichols, chairman of the California Air Resources Board, testified at a hearing with federal officials in a region of central California that has some of the nation’s worst air pollution.

State Attorney General Xavier Becerra said California could not afford to retreat in the fight against climate change, citing wildfires and high asthma rates among children in the state’s San Joaquin Valley, where residents, environmentalists and state officials testified at the first of three nationwide hearings on the mileage plan.

“Stopping us from protecting our people, our jobs and economy or our planet is like trying to stop a mother from protecting her child,” he said.

The proposal announced by the Trump administration would freeze U.S. mileage standards at levels mandated by former President Barack Obama for 2020.