WASHINGTON — The head of the Environmental Protection Agency faced down hostile critics yesterday in his first committee appearance before the Democratic-led Congress, denying accusations that agency decisions last year rolled back environmental safeguards.

“These decisions and actions all accelerate the pace of environmental protection. They all deliver environmental results,” EPA Administrator Stephen Johnson told the Senate Environment and Public Works Committee.

“Nobody’s fooled by this,” the new committee chair, Senator Boxer, a Democrat of California, said. “EPA has gone too long without meaningful oversight,” she said, contending the changes “benefit polluters’ bottom line and they hurt our communities.”

At issue were a number of changes EPA made last year, including a new policy that reduces the role of scientists in setting air pollution standards; a move to raise the threshold for reporting releases of toxic chemicals, and the shuttering of five agency libraries where the public could look at scientific and health documents.

A Government Accountability Office study released yesterday said the EPA did not adhere to its own rule-making in making the changes to toxic chemicals reporting. The Toxic Reporting Inventory changes, the GAO said, “will likely have a significant impact on information available to the public about dozens of toxic chemicals” at facilities nationwide.

Mr. Johnson said the new rule encourages businesses to adopt better waste management practices by allowing them to reduce emissions reporting if they do so. “My interest is to do anything I can to encourage businesses to reduce emissions,” he said.

The EPA libraries were closed, Mr. Johnson said, because they got barely any visitors and the information that they housed was being put on the Internet.

Ms. Boxer confronted him with internal agency e-mails and Web postings indicating more libraries were closed than he seemed to be aware of and suggesting EPA staff was ordered to throw away scientific journals at one library.

Mr. Johnson said some journals were discarded after they were contaminated by mold in a flood, and that in some cases documents were destroyed if there was more than one copy of them.