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WASHINGTON — President Trump on Monday announced he would nominate David Bernhardt, a former oil lobbyist and current deputy chief of the Interior Department, to succeed Interior Secretary Ryan Zinke, who resigned amid allegations of ethical missteps.

In a message on Twitter, Mr. Trump wrote, “David has done a fantastic job from the day he arrived, and we look forward to having his nomination officially confirmed!”

While Mr. Zinke had been the public face of some of the largest rollbacks of public-land protections in the nation’s history, Mr. Bernhardt was the one quietly pulling the levers to carry them out, opening millions of acres of land and water to oil, gas and coal companies. He is described by allies and opponents alike as having played a crucial role in advancing what Mr. Trump has described as an “energy dominance” agenda for the country.

“Bernhardt has really been running the show, directing the policy shop in a very strong way,” said Mark Squillace, an expert on environmental law at the University of Colorado Law School.