Environmental Protection Agency staff warned the agency's chief last year that the state of California has a strong legal case for regulating vehicle emissions, according to documents reviewed and described by Senate staff.

Senate Democrats are expected to use the finding to confront the Bush administration at a hearing today that will focus on the administration's decision last month to deny California permission to regulate automobile carbon-dioxide emissions.

The evidence of conflict between the agency's staff and EPA Administrator Stephen Johnson will intensify a debate over the administrator's decision late last year to block the state from going forward with the nation's first vehicle carbon-dioxide-emissions rules. The issue is of critical importance to the auto industry, which doesn't want to face what is sees as a patchwork of carbon-dioxide restrictions. The industry has argued that climate change is a problem that should be handled at the federal level.

Mr. Johnson is scheduled to testify today before the Senate Environment and Public Works Committee, led by California Democrat Barbara Boxer, who suggested yesterday that Mr. Johnson should be dismissed.

"He needs to be held accountable," Sen. Boxer said. She said she is seeking to reverse Mr. Johnson's decision, and that "the president could fire him, if he felt as I do."