WASHINGTON — The Environmental Protection Agency's top science adviser on Wednesday defended his boss for allowing more ozone pollution than the EPA's advisory panels recommended and for holding meetings with White House officials about pollution risks that are kept secret from Congress and the public.

George Gray, the EPA's assistant administrator for research and development and its science adviser, told the Senate Environment and Public Works Committee that the EPA's 7,000 scientists conduct research free of political influence and speak openly about their work.

Gray insisted the EPA's work is transparent even though it holds closed meetings with the White House Office of Management and Budget and other government agencies when it considers the risks from toxic chemicals. Democratic senators said the closed meetings were an opportunity for interference from government officials and industry groups.

Sen. Sheldon Whitehouse, D-R.I., said the committee had to determine whether the EPA was fulfilling its mission to protect the environment and health, "without regard to politics or special interests, without fear or favor. The increasing weight of the evidence suggests that it is not."

The EPA administrator, Stephen Johnson, declined to testify.

"The last few times Mr. Johnson has appeared before us, he has been less than forthcoming, as evasive and unresponsive as (former Attorney General) Alberto Gonzales," Whitehouse said.

He added that the forced resignation of EPA regional administrator Mary Gade, who had been investigating dioxin contamination in Michigan by Dow Chemical, "smacks of the U.S. Attorney scandal at the Justice Department last summer." Like the nine U.S. attorneys the White House fired, Gade was well regarded and had received strong performance evaluations, he said, adding, "her forced resignation reeks of political interference."

Gray declined to discuss Gade's ouster.

Sen. Amy Klobuchar, D-Minn., said Johnson rejected 1,700 peer-reviewed scientific studies and the unanimous recommendations of its own advisory committees when he set the new ozone standard. Johnson made the standard tougher than it had been, but not as strong as the advisory committees and many medical associations wanted.

Gray said Johnson didn't ignore them, but considered their advice and made a different decision based on his own view of the science.

"EPA has a proud history of producing science that has informed decisions to protect human health and the environment," Gray said.

He said science was "but one aspect" of EPA's regulatory decisions. Other considerations, he said, included technological feasibility, costs of implementing policies and "local autonomy versus federal control," he said.

Sen. Barbara Boxer, chairwoman of the environment committee, said courts have ruled that the EPA is not supposed to consider costs. That's the job of Congress, she said.

"A clear pattern has emerged at EPA," Boxer said. "When it comes to who wins and who loses, time and time again, the polluting special interests come out on top, at the expense of the health of the American people."

Klobuchar asked Gray about his membership on the board of the Annapolis Center, a group that downplays the risks of global warming and air pollution, from 1995 to 2000. Gray declined to discuss it.

Several Democrats on the committee criticized the Bush administration's practice of involving other government agencies in closed sessions with the EPA when it was assessing pollution risks.

Sen. Lamar Alexander, R-Tenn., defended Johnson and the EPA. Alexander said he often ignored the advice of his Senate staff when he knew something better than they did, and he said that senators held private Republican and Democratic meetings that were closed to the press and the public.

The General Accountability Office recommended that all input, particularly from agencies that might be affected by pollution policies, should be publicly available and that the EPA should streamline its lengthy assessment process. The EPA rejected the recommendations.

The Union of Concerned Scientists, an environmental group, surveyed some 5,500 EPA scientists last year and found the agency was "under siege from political pressures," Francesca Grifo, a senior scientist with the group, told the Senate panel.

She said 1,586 scientists completed the surveys, and 889 of them said they'd experienced at least one incident of political interference in the past five years.

When Whitehouse asked him about the figure, Gray responded, "I'll say 889 is a number that is unacceptable to me."