WASHINGTON — The Trump administration will extend by one year a deadline for states to comply with a major Obama-era regulation on emissions of a smog-causing pollutant that spews from tailpipes and smokestacks.

In October 2015, the Environmental Protection Agency set a new national standard for ozone, a smog-causing gas that often forms on hot, sunny days when chemical emissions from power plants, factories and vehicles mix in the air. The standard tightened emissions to 70 parts per billion down from 75 parts per billion, as was set in 2008. Smog has been linked to asthma, heart and lung disease, and premature death.

In a letter sent Tuesday to governors, Scott Pruitt, the E.P.A. administrator, delayed a requirement for states to submit measurements of their 2015 ozone levels by 2017. The move is the latest in a series of steps taken by Mr. Pruitt to relax or delay several major environmental regulations put forth by the Obama administration under the Clean Air and Clean Water Acts. Mr. Pruitt, the former attorney general of Oklahoma, had in his previous position taken a leading role in many multistate lawsuits against those regulations, calling them deeply burdensome to industry.“We share the goal of clean air, a robust economy and stronger, healthier communities,” Mr. Pruitt said in a statement. “We are committed to working with states and local officials to effectively implement the ozone standard in a manner that is supportive of air quality improvement efforts without interfering with local decisions or impeding economic growth.”

The oil-refining industry had led a multiyear lobbying campaign against the ozone rules, complaining that the regulations would require them to install costly equipment to remove the smog-causing chemicals from gasoline and other fuels. And Republican lawmakers who have long complained against President Barack Obama’s regulatory agenda cheered the delay.

But environmental groups assailed it as a move by allies of the fossil fuel industry granting favors to industry cronies.

“The delay is flagrantly illegal as well as a direct assault on our right to breathe safe, clean air,” said John Walke, the director of the clean air program at the Natural Resources Defense Council, an advocacy group.