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.”

The extraordinary about-face reflects the onset of an experiment in President Trump’s Washington that is meant to fundamentally reorder the relationship between government and business. Across the federal government, lobbyists and lawyers who once battled regulations on behalf of business are now helping run the agencies they clashed with.

Mr. Trump and his team believe that loosening the regulatory grip on business will help the economy, create jobs and allow Americans “to share in the riches,” as he said during the campaign. But in the energy field, environmentalists, Democrats and even some in the industry fear the efforts will backfire, harming health and safety without creating much economic benefit.

The E.P.A. has not yet made a public response to Devon’s new posture, and Mr. Pruitt declined to comment for this article. But the new approach follows a series of important victories for the energy industry in Washington that could reshape environmental policy on a national scale and undermine the Obama administration’s campaign to combat climate change.