WASHINGTON  Lisa P. Jackson, chosen to head the Environmental Protection Agency, said at her confirmation hearing Wednesday morning that her first task would be to restore scientific and legal integrity to an agency battered by charges of political interference and coziness with industry.

But she evaded questions on whether as administrator of the E.P.A. she would immediately grant authority to California and 16 other states to regulate vehicle tailpipe emissions, promising only a speedy review of the issue. Nor did she directly answer questions on whether and how the agency would address regulation of carbon dioxide under the Clean Air Act, an authority granted the E.P.A. by the Supreme Court in 2007.

The Bush administration has declined to act on either matter.

Her promise to be guided by science and the law was an implicit rebuke of the management of the E.P.A. under President Bush, where career officials’ recommendations were sometimes ignored in decisions regarding lead in the air, arsenic in water, and carbon dioxide in the atmosphere.

“Science must be the backbone of what E.P.A. does,” Ms. Jackson said in her opening statement to the Senate Environment and Public Works Committee. “If I am confirmed, I will administer with science as my guide. I understand the laws leave room for policymakers to make policy judgments. But if I am confirmed, political appointees will not compromise the integrity of E.P.A.’s technical experts to advance particular regulatory outcomes.”