Dennis Cook / AP Sen. Barbara Boxer, D-Calif., presides over a hearing on Capitol Hill on Thursday to discuss why California's request for a greenhouse gas waiver was denied.

WASHINGTON — The head of the U.S. Environmental Protection Agency stood defiantly Thursday behind his decision to deny California a waiver to regulate tailpipe emissions, even though newly released documents suggest his staff backed the exemption.

EPA Administrator Stephen Johnson said the decision was his to make and that he came to "an independent judgment" that California did not have "compelling and extraordinary conditions" to set its own greenhouse gas emission standards.

"My job is to make the right decision, not the easy decision," Johnson said.

"This is not a popularity contest," he later said.

Johnson's explanation infuriated Democrats on the Senate Environment and Public Works Committee, which hauled him before the panel to explain his rationale.

"The mission of the EPA is to protect human health and the environment," said Sen. Barbara Boxer, D-Calif., the committee chairwoman. "The administrator's decision does neither."

Government's in the way

Sen. Frank Lautenberg, D-N.J., said while it is bad enough when the federal government fails to lead, "it is even worse when the federal government gets in the way of states that are trying to act in the absence of that leadership."

Johnson's decision, announced last month, denies California the waiver it needs under the federal Clean Air Act to impose what would have been the nation's toughest greenhouse gas standards on cars, trucks and sport utility vehicles.

California's rules, which the state Legislature passed in 2002, would force automakers to reduce greenhouse gas emissions by 30 percent in new cars and light trucks by 2016, starting with the 2009 model year.

But California can't impose the standards without a waiver from the EPA. Eighteen other states have adopted California's standards or are in the process of adopting them. They, too, are prohibited from implementing the rules under Johnson's decision.

California and 15 other states sued the EPA earlier this month over Johnson's decision.

Documents obtained by Boxer's committee, excerpts of which were made public Wednesday, indicate that EPA staff had concluded that California had "compelling and extraordinary conditions" for imposing the new standards and that the EPA was likely to lose if the issue should end up in court.

But Johnson downplayed the significance of those findings. He asked the EPA staff to provide him with "the full range of options available," as well as their possible ramifications, he said. In the end, however, "it was my decision," Johnson said.

Johnson denied that he was under political pressure from the White House to reject the waiver. "I was not directed by anyone to make the decision," he said.

Johnson said he denied the waiver because global warming is a problem that poses challenges for the entire nation and the world. As a result, national fuel economy standards are preferable to allowing individual states to impose their own regulations, he said.

He announced his denial of the California waiver Dec. 19, the same day President Bush signed into law an energy bill that requires automakers to increase average fuel economy ratings to 35 mph by 2020.

Johnson argues that the federal fuel efficiency standard is superior to the California program and would provide a national approach to reducing greenhouse gas emissions from cars.

Boxer, however, accused him of bowing to special interests. "You are walking the American taxpayers into a lawsuit that you are going to lose," she warned.

'Negative light' on EPA

Boxer also released a letter sent to Johnson by the heads of unions that represent EPA employees. The union officers complained that Johnson's denial of the California waiver is perceived as politically motivated and has cast "a negative light" on the EPA.

Many workers are troubled by Johnson's decision to overrule the recommendation of the agency's technical and legal staff, the union leaders said. They warned that his decision could have a devastating impact on employee morale and could affect the agency's ability to attract other talented workers.

Johnson did get some support during Thursday's hearing.

Oklahoma Sen. James Inhofe, a global warming nonbeliever who is the committee's top Republican, dismissed the hearing as "theater" and argued Johnson had made the right decision in denying the waiver.

Douglas Haaland, director of member services for the California Assembly's Republican Caucus, also testified that California's waiver would represent "a radical change in direction." Haaland praised Johnson's decision as "a reasoned response to a process that has been allowed to spin out of control."