Washington • Former oil and gas lobbyist David Bernhardt was confirmed by the Senate on Thursday to lead the Interior Department, an agency that controls nearly half a billion acres of public land and the vast amount of oil and gas mineral resources resting beneath it.

The 56-41 vote Thursday promoted Bernhardt from the department's acting secretary, a job he assumed after his predecessor Ryan Zinke resigned amid numerous investigations into his behavior and management of the agency. Bernhardt had served as Zinke's deputy until his departure in December.

Bernhardt's extensive experience at the Interior Department, where he served as solicitor during President George W. Bush's administration, was cited by his supporters who said he is more than qualified to lead the agency.

But his work as a lobbyist for the oil and gas industry in the West, as well as large water utilities, led to concerns about conflicts of interest. The Interior Department oversees 700 million acres of public lands and 1.7 billion acres offshore, and it works closely with some of Bernhardt's former clients.

Bernhardt has so many potential conflicts of interest that he carries an index card listing companies and people he should avoid. Concerns over ethics led to a heated confrontation between a Democrat who opposed Bernhardt's nomination and a Republican who opposed it at his confirmation hearing.

Sen. Ron Wyden, D-Ore., said Bernhardt came to his office and assured him that he would follow ethics rules. Shortly after the meeting, Wyden said, he was startled to see that Bernhardt was the subject of a newspaper article that said he intervened on behalf of the oil industry and others to stop a U.S. Fish and Wildlife Service analysis that said certain toxic pesticides used by such businesses threatened endangered animals.

"Why would you come to my office and lie?" Wyden asked. The actions "make you sound like just another corrupt official," the lawmaker said.

Wyden's statement was immediately countered by Bernhardt's friend and fellow Coloradan, Sen. Cory Gardner, a Republican who said Democrats exhibited a double standard by supporting former Interior Secretary and petroleum engineer Sally Jewell but not Bernhardt.

In the end, the Energy and Natural Resources Committee approved Bernhardt's nomination by a 14-6 vote. Several Democrats joined Gardner and Chairwoman Lisa Murkowski, R-Alaska, in supporting the nominee.

“I will work closely with Chairman Murkowski and my colleagues to ensure Mr. Bernhardt commits to the highest standards of ethics, not just in the letter of the law but truly the spirit of the law,” said Joe Manchin, D-W.Va.

Shortly before the Senate vote, Sen. Martin Heinrich, D-N.M., explained his support of Bernhardt.

"I need to be able to pick up the phone and talk to the secretary of interior on a regular, regular basis because these things have direct impacts on New Mexico," Heinrich said Wednesday. "We didn't win the election in 2016, so I'm not going to get my choice for secretary of interior. In the meantime, I have to be able to work with these folks."

Heinrich expressed particular concern about potential oil and gas drilling in the Chaco Canyon area near massive stone ruins considered sacred to the descendants of the ancient Pueblo civilization: "I'm going to put my state, and the protection of public lands in my state, ahead of the sort of political battle that happens in Washington, D.C."

On the day of the Senate vote, Gardner again denounced Bernhardt's opponents and said the "Washington, D.C., political smear machine has been working overtime" to bring down a good man.

Democrats and conservation groups in turn say Bernhardt has worked overtime to roll back key regulations protecting public lands and wildlife.

With Bernhardt acting as an influential deputy under Zinke, the Interior Department held oil and gas lease sales that resulted in more than a billion dollars in revenue for the national treasury.

But the agency also weakened enforcement of the 100-year-old Migratory Bird Treaty Act, allowing individuals and companies to kill scores of protected birds so long as investigators determine it was not intentional, reversing a longstanding rule.

The pair also oversaw a rollback of National Park Service rules on federal land in Alaska. Now, hunters can kill mother bears and their cubs sleeping in dens; hunters may shooting animals from boats as game swims.

Sen. Amy Klobachur, D-Minn., said Thursday that she opposed Bernhardt's nomination for several reasons, including his role in weakening enforcement of the law to protect birds and "stacking the deck in favor of the fossil fuel industry."

Like other Democrats, Klobachur decried his actions to limit opportunities for the public to comment on the department's policy decisions and Bernhardt's directive to agency employees to not factor climate and environmental effects into guidance.

Under Bernhardt, she said, the Interior Department has downplayed climate science and has made decisions and rules "that will accelerate its effect. The question is not is it happening . . . the question is what will we do about it," she said.

The Washington Post’s Dino Grandoni contributed to this report