SACRAMENTO, Calif. (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 documents provided Friday by the EPA omitted key details, including a presentation that Senate aides said predicted EPA would lose a lawsuit if it went to court for denying California's waiver.

The refusal to provide a full explanation 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.