While Democrats, who have called for his resignation, sought to force Mr. Pruitt to accept culpability for a variety of ethical missteps, he denied knowledge of or responsibility for the actions in question. Republicans, after briefly chastising Mr. Pruitt in their opening remarks, asked friendly questions that appeared calculated to allow him to talk about his policy proposals.
As reports about Mr. Pruitt have continued to increase, some White House staff members have urged Mr. Trump to fire the E.P.A. chief. Some Republican leaders have called for his resignation, and many in Mr. Pruitt’s own party have called for investigations into his actions. But analysts who watched his performance on Thursday said he did well.
Representative Ken Calvert, Republican of California and chairman of the appropriations subcommittee where Mr. Pruitt testified in the afternoon, called the administrator’s appearance “very professional.”
Asked if Mr. Pruitt should resign he said, “No.”
Ultimately, of course, the only opinion about Mr. Pruitt’s fate that matters is the president’s.
“I think his effort will be well received by the president,” Mr. Maisano said. He has more explaining to do, but it was a good effort to mend fences. There were no lethal blows.”
Mr. Pruitt is now the subject of 10 federal investigations, including questions about his office’s illegal purchase of a secure phone booth, his condominium rental agreement with the wife of an energy lobbyist, and accusations that he demoted or sidelined E.P.A. employees who questioned his actions.
Committee Democrats queried him sharply about the reports of his ethical lapses and pressed Mr. Pruitt on his rollbacks of environmental rules, in particular, a new policy, proposed this week, that would limit the E.P.A.’s use of scientific research in crafting new health and environmental rules. Scientists have deplored the proposed rule, saying that it would significantly limit the agency’s use of rigorous science.
“Administrator Pruitt has brought secrecy, conflicts of interest and scandal to the E.P.A.,” said Representative Frank Pallone Jr. of New Jersey, the ranking Democrat on the House Energy and Commerce Committee, where Mr. Pruitt testified Thursday morning. “You are unfit to hold public office and undeserving of the public trust,” he said. “Every indication we have is you really should resign.”
Greg Walden, Republican of Oregon and the chairman of the House Energy committee, offered light criticism before moving on to praising Mr. Pruitt for his efforts to roll back environmental regulations. “I am concerned that the good progress being made on the policy front is being undercut by allegations of your management of the agency and use of its resources,” he said. “These issues are too persistent to ignore.”
Conservative lawmakers from fossil-fuel producing states, who have long pushed for the rollback of E.P.A. regulations, bypassed even slight criticism of Mr. Pruitt, attributing the scrutiny on his actions to a political witch hunt.
Representative David B. McKinley, Republican of West Virginia, told Mr. Pruitt sympathetically that the attacks on him “have an echo of McCarthyism.”
In many ways, the past 14 months of Mr. Pruitt’s tenure has been building to this moment.
As Oklahoma’s attorney general, he made a name for himself aggressively battling the agency he now leads. Mr. Pruitt’s confirmation was fiercely opposed by Democrats, environmentalists and even E.P.A. employees. Since taking the helm of the agency, Mr. Pruitt has worked to strip the E.P.A. of funding, reduce its staff and curb its ability to develop new regulations on fossil fuel pollution.
No E.P.A. director in history has achieved Mr. Pruitt’s level of notoriety. Since the agency was formed, its administrators have been second-tier Washington figures. But Mr. Pruitt’s antagonism toward climate science has made him a nationally-prominent and divisive figure.
Critics said that more than the ethical and spending issues, the real damage to the E.P.A. has been Mr. Pruitt’s systematic weakening of the agency’s ability to protect the environment and public health. While Mr. Pruitt’s performance in Thursday’s hearings may make or break his future within the Trump administration, many said his legacy was already set.
“It’s just been a flagrant, shameless series of calculated decisions to dismantle the country’s most successful domestic enterprise,” William K. Reilly, who led the E.P.A. under the first President George Bush, said of Mr. Pruitt’s leadership. “It’s really a national tragedy,” he said.
At Thursday morning’s hearing, Representative Joe Barton of Texas, who has long denied the overwhelming evidence of human effects on climate change, offered sympathy. “Mr. Pruitt, you’re not the first victim of Washington politics,” he said.
Democrats unsuccessfully sought to pin down Mr. Pruitt on questions about his expenditures, and to force him to accept culpability for some the actions now under investigation.
Representative Tony Cárdenas, a California Democrat, asked about Mr. Pruitt’s soundproof booth, installed in his E.P.A. office at a cost of $43,000. The Government Accountability Office has ruled that the expenditure broke the law.
“I was not aware of the approval of the $43,000,” Mr. Pruitt told him, “and if I had known about it, congressman, I would not have approved it.”
Mr. Cárdenas responded that “if someone was spending $43,000 in my office, I would know about it.”
Representative Diana DeGette, a Colorado Democrat, launched into questions about Mr. Pruitt’s involvement in real estate deals in Oklahoma that have been reported in The New York Times, referring to the purchaser of his home as a “shell company.”
“It’s not a shell company,” he said quickly, and added that such financial structures were commonly used to purchase real estate in Oklahoma.
She then asked Mr. Pruitt whether he had paid taxes on rent he received. He said the issue had been handed over to an accountant.
“I’m not doing this to hassle you. I’m doing this as an elected official,” Ms. DeGette said as she ended her questions. “Everything we do has to be to the highest ethical standards.”
Representative Paul Tonko, the ranking Democrat on the House Energy’s subcommittee on the Environment, pressed Mr. Pruitt on his claims that he was unaware that the E.P.A. had used an obscure legal provision to grant hefty raises to political appointees, bypassing approval by the White House. Mr. Pruitt has said the decision was taken by his chief of staff, Ryan Jackson.
“Did you authorize Mr. Jackson to sign those documents for you?” Mr. Tonko asked.
“I was not aware of the amount and I was not aware of the bypassing that was going on,” Mr. Pruitt replied.
Even some Republicans criticized Mr. Pruitt for repeatedly blaming his staff.
“If you say give me a phone booth, and your staff does it, you should say, I’m at fault,” said Representative John Shimkus, Republican of Illinois, the chairman of the House Energy subcommittee, speaking to reporters after the morning hearing. “It’s never good to blame your staff. Or at least do it behind closed doors.”
And Representative Anna G. Eshoo, a California Democrat, used her turn at questioning to try to get Mr. Pruitt to accept culpability. “You have a solid record of violating ethics rules from the state level to the federal government,” she told Mr. Pruitt. “I think it’s an embarrassment.” And then she asked, “Do you have any remorse? Yes or no?”
Mr. Pruitt responded: “I think there are changes I’ve made already. I’ve made a change from first class to coach travel.” Ms. Eshoo returned to her call for a yes-or-no answer, and asked Mr. Pruitt whether he would reimburse the government. He launched into a long response, but she cut him off.
“With all due respect, I may be elected, but I’m not a fool,” she said. “This is not ‘dodge-question’ day.”
An earlier version of this story gave the incorrect home state for Representative John Shimkus. He represents Illinois, not Pennsylvania.