If confirmed by the Senate, Mr. Bernhardt will become one of two former lobbyists overseeing the nation’s top environmental agencies. The other is Andrew Wheeler, a former coal lobbyist who heads the Environmental Protection Agency. Like Mr. Bernhardt, Mr. Wheeler was a deputy who ascended to lead his agency after his former boss — Scott Pruitt, in the case of the E.P.A. — resigned amid allegations of corruption.

As a partner in the law firm Brownstein Hyatt Farber Schreck, Mr. Bernhardt lobbied for the oil companies Cobalt International Energy and Samson Resources. His legal clients included the Independent Petroleum Association of America, which represents dozens of oil companies, and Halliburton Energy Services, the oil and gas extraction firm that was led by Dick Cheney before he became vice president.

As deputy secretary of the Interior Department, Mr. Bernhardt was the lead author of a revision of a program to protect tens of millions of acres of habitat of the imperiled sage grouse, a puffy-chested, chicken-like bird found in 10 oil-rich Western states. His final sage grouse plan, issued this month, would strip away protections from about nine million acres of the bird’s habitat, a move that, in a stroke, opened up more land to oil and gas drilling than any other single policy action by the Trump administration.

Mr. Bernhardt is also the chief author of a major plan, expected to be finalized and made public in the days or weeks after his Senate confirmation, that would allow the federal government to lease almost any part of the United States coastline to oil and gas companies for offshore drilling.

In Thursday’s Senate hearing, Mr. Bernhardt also faced criticism for his actions during the 35-day government shutdown this year.

During that time, while thousands of federal employees were furloughed and government services shut down, Mr. Bernhardt brought back workers in offices that permit and inspect oil and gas drilling. In that period, those workers approved 15 new leases for drilling on public lands as well as 71 new permits for offshore drilling, and more than 50 recipients of the offshore drilling permits were companies that sit on the board of directors of the National Ocean Industries Association, a former client of Mr. Bernhardt’s.

Senator Catherine Cortez Masto, Democrat of Nevada, pressed Mr. Bernhardt as to why he led the push to continue the agency’s work on drilling but not on conservation, maintaining national parks or permitting renewable energy programs.