FREMONT COUNTY, Wyo. — In a gas field here in Wyoming’s struggling energy corridor, nearly 2,000 miles from Washington, the Trump administration’s regulatory reversal is crowning an early champion.

Devon Energy, which runs the windswept site, had been prepared to install a sophisticated system to detect and reduce leaks of dangerous gases. It had also discussed paying a six-figure penalty to settle claims by the Obama administration that it was illegally emitting 80 tons each year of hazardous chemicals, like benzene, a known carcinogen.

But something changed in February just five days after Scott Pruitt, the former Oklahoma attorney general with close ties to Devon, was sworn in as the head of the Environmental Protection Agency.

Devon, in a letter dated Feb. 22 and obtained by The New York Times, said it was “re-evaluating its settlement posture.” It no longer intended to move ahead with the extensive emissions-control system, second-guessing the E.P.A.’s estimates on the size of the violation, and it was now willing to pay closer to $25,000 to end the three-year-old federal investigation.

Devon’s pushback, coming amid an effort to ease a broad array of federal environmental rules, is the first known example under the Trump administration of an accused polluter — which has admitted violating the law — backing away from a proposed environmental settlement. It is already being hailed by other independent energy companies as a template for the future.

“Not in our wildest dreams, never did we expect to get everything,” said Kathleen Sgamma, president of Western Energy Alliance, a Denver-based association of independent oil and gas companies. “We were kind of used to getting punished.”