By Richard Simon

WASHINGTON — Under grilling by a hostile Senate committee Thursday, Environmental Protection Agency Administrator Stephen L. Johnson defended his decision to deny California permission to implement its own global-warming law, even as legislators launched an effort to force its reversal.

"I was not directed by anyone," Johnson said at a hearing before the environment and public works committee, denying he had been influenced by political pressure from the White House or anyone else. "This was solely my decision."

Johnson failed to mollify Sen. Barbara Boxer (D-Calif.), the committee chairwoman and perhaps his fiercest critic, who vowed to press ahead with her investigation into how the EPA chief reached his decision. Within hours of his testimony, she introduced legislation -- co-sponsored by 17 senators, including Democratic presidential front-runners Hillary Rodham Clinton of New York and Barack Obama of Illinois -- to overturn the decision.

In his first Capitol appearance since denying California's request late last month, Johnson drew the ire of other Democratic senators whose states also want to enact greenhouse-gas-emission standards for new cars and trucks that are more stringent than the federal government's.

"Your agency's decision to deny California a waiver just defies logic to me," Sen. Amy Klobuchar (D-Minn.) told Johnson. "It's clearly a decision, I believe, that's based on politics and not on fact."

Boxer called Johnson's decision "unconscionable" and accused him of going against the advice of his legal and science advisors and siding instead with the auto industry, which has resisted California's efforts to implement its tailpipe law.

'The right decision'

Johnson responded: "I am bound by the criteria in the Clean Air Act, not people's opinions. My job is to make the right decision, not the easy decision."

Johnson's only Senate defender at the hearing was James M. Inhofe of Oklahoma, the sole Republican in attendance and perhaps Congress' leading skeptic on global warming. Inhofe dismissed the proceedings as "theater."

Thursday's hearing was intended to help build support for a legislative effort to overturn the decision, but critics may stand a better chance in the courts than in Congress. California and 15 other states have sued the administration to overturn the decision; legislation is likely to face a presidential veto.

In denying California's request, Johnson has said that a nationwide climate change strategy is preferable to a "patchwork of state rules."

He has said that the tougher fuel-economy rules in the recently enacted federal energy bill would go a long way to reduce emissions nationwide.

Climate change, Johnson said at the hearing, is "a global problem requiring a global solution -- at least, at a minimum, a national solution."

He added: "It's not exclusive to California."

Boxer has accused Johnson of stonewalling the committee's request for documents on how he reached the decision. She displayed oversize copies of largely blank documents provided by the EPA.

The EPA agreed to let Boxer's staff see some documents, as long as they did not photocopy the documents and as long as they inspected them under the supervision of agency employees.

Boxer's aides copied the documents by hand and made the contents public anyway, saying they show that Johnson acted against the recommendations of his legal and scientific staff.

Johnson said that, since California is suing the EPA over the issue, his agency was protecting documents under attorney-client privilege. Boxer replied that Johnson had "no privilege" to withhold documents from Congress.

Reminder of oath

Democrats expressed skepticism that Johnson was not influenced by political considerations, reminding him a number of times that he was under oath. Officers of unions representing EPA scientists, engineers and other technical specialists also weighed in, sending a letter to Johnson on Thursday that expressed "dismay and concern over the damage to EPA's reputation" after his denial of California's request.

"We lament that your decision -- perceived by many as having been politically motivated and prompting congressional investigations -- has cast a negative light on our agency," they wrote.

Johnson refused to discuss his conversations with President Bush. "Any conversations that I have with the president are between the president and myself," he told the panel. But he said he made his decision "based upon the facts presented to me."

Democrats used the hearing to attack the Bush administration as failing to confront global warming aggressively enough.

"This administration has taken the word 'environment' out of 'Environmental Protection Agency,' " said Sen. Bernie Sanders (I-Vt.)

Sen. Frank R. Lautenberg (D-N.J.) added: "It's bad enough when the federal government fails to lead. But it's even worse when the federal government gets in the way of states that are trying to act in the interest of the public and in the absence of leadership from the EPA."