WASHINGTON — Sen. David Vitter led the critical questioning Thursday of the president’s choice to head the Environmental Protection Agency during her initial confirmation hearing.

Vitter, R-La., the ranking Republican on the U.S. Senate Environmental and Public Works Committee, has remained on the offensive with the EPA recently, voicing concerns about proposed regulations; an alleged lack of transparency; and what he calls the administration’s “sue-and-settle practices” to seek resolutions in court after the federal government is sued by environmental organizations.

The nominee for EPA administrator is Gina McCarthy, who currently heads the EPA’s air and radiation office. She would replace outgoing EPA Administrator Lisa Jackson, of New Orleans, whom Vitter has called the worst EPA head ever.

The Democratic-led committee is expected to approve McCarthy at its next meeting, but a fight is expected on the U.S. Senate floor over her confirmation.

“I am concerned, as you know, that the central functions of the agency have been obfuscated by ideology, frustrated by a severe lack of transparency, undermined by science the agency keeps hidden and implemented without regard for economic consequences,” Vitter said Thursday.

Vitter and other Republicans have sought answers from McCarthy regarding transparency with EPA email accounts and federal records requests, the scientific data and cost-benefit analyses — if applicable — used to justify Clean Air Act rules, and more.

Vitter said only about “one and one-quarter” of five requests were adequately answered by her. “I’m quite frankly disappointed with the responses we’ve gotten,” he said.

Committee Chairwoman U.S. Sen. Barbara Boxer, D-Calif., and other Senate Democrats were quick to come to McCarthy’s defense.

“Gina McCarthy, you are one of the best qualified nominees ever to come before this committee,” Boxer said. “Your combination of experience, intelligence, energy, expertise and integrity will make you an effective EPA administrator.”

She also argued that McCarthy has plenty of bipartisan experience, having worked for multiple Republican governors, including former Massachusetts Gov. Mitt Romney.

“It is my fervent hope that these issues will be resolved quickly,” Boxer said, regarding the questioning by Vitter and other Republicans.

McCarthy said she is “deeply honored” by the nomination and that she wanted to help create a “cleaner, safer world … while enjoying an even more prosperous economy.”

She said she wants to improve water safety and fix the nation’s “antiquated chemical safety laws.” She argued she will work for “EPA’s use of science to be rigorous and transparent.”

Sen. Bernie Sanders, No Party-Vt., pressed on the issues of global warming and climate change, calling it the “most serious planetary crisis that we face.”

McCarthy said the “science is overwhelming” that global warming is real. “I do believe that man-made emissions contribute to global warming,” she said.

Vitter criticized the EPA practice of its administrators using a secondary work email address, which he argued could be used to hide records. He also took note of a “pattern of abuse” of EPA leaders conducting business on personal email accounts.

“I do not conduct business through private email,” McCarthy responded, adding that she shares Vitter’s concerns about “transparency and accountability.”