By SAMANTHA YOUNG
Associated Press Writer

SACRAMENTO (AP) … Invoking executive privilege, the Environmental Protection Agency on Friday refused to provide lawmakers with a full explanation of why it rejected California’s greenhouse gas regulations.

The EPA informed Sen. Barbara Boxer, D-Calif., that many of the documents she had requested contained internal deliberations or attorney-client communications that would not be shared with Congress.

“EPA is concerned about the chilling effect that would occur if agency employees believed their frank and honest opinions and analysis expressed as part of assessing California’s waiver request were to be disclosed in a broad setting,’’ EPA’s associate administrator Christopher P. Bliley wrote.

The document dump is the latest twist in a congressional investigation into why the agency denied California permission to impose what would have been the country’s toughest greenhouse gas standards on cars, trucks and sports utility vehicles.

In denying California’s waiver last month, EPA Administrator Stephen L. Johnson told Gov. Arnold Schwarzenegger that the federal government is implementing its own national fuel efficiency standard.

Johnson’s decision spurred several congressional investigations and a legal appeal earlier this month by California and 15 other states.

Boxer and Rep. Henry Waxman, D-Calif., for weeks have asked the agency for more information about why it denied California’s plan.

More than a week after a deadline set by Boxer, the agency gave her environmental committee a box of documents with numerous pages of the relevant documents whited out and missing key information, Boxer said.

She called the agency’s failure to comply with a legitimate congressional request “"an insult to the American people and a dereliction of duty.’’

Boxer had threatened to subpoena the agency if it did not turn over the waiver documents. She said she would continue her quest for all the information.

The documents provided Friday by the EPA omitted key details, including a presentation prepared for Johnson that Senate aides said predicted the agency would likely lose a lawsuit if it went to court for denying California’s waiver.

Everything except the titles was omitted from the 15-page Power Point presentation provided to the committee, according to copy of the document e-mailed to The Associated Press.