But during a hearing, Johnson refused to say whom he had spoken to about his decision to deny California and 15 other states, including Pennsylvania and New Jersey, permission to adopt their own more stringent standards designed to reduce global warming.

"I don't know what you're hiding," said Sen. Barbara Boxer (D., Calif.), the chairwoman of the Environment and Public Works Committee. "It's as if you're taking the Fifth Amendment."

California officials, dissatisfied with weaker federal rules governing tailpipe emissions, asked for a waiver so the state could adopt its own standards. The move was opposed by the auto industry, which argued that only one national standard should apply.

According to internal EPA documents released by Boxer, the agency's career scientists had advised Johnson to grant California's request.

One career EPA official even wrote talking points for former EPA Administrator William K. Reilly, who had been enlisted by California proponents to lobby Johnson.

"It is obvious to me that there is no legal or technical justification for denying this," one of the talking points read. "The law is very specific about what you are allowed to consider, and even if you adopt alternative interpretations that have been suggested by automakers, you still wind up in the same place."

On Dec. 17, after conferring with his political appointees in EPA, Johnson rejected the California request.

California and the other states, including Pennsylvania and New Jersey, promptly sued, alleging that California had met all the requirements to obtain the waiver. Among the internal EPA documents released by Boxer was one predicting that a decision to reject the California waiver likely would be overturned by the courts.

Johnson yesterday cited the pending lawsuit as one reason he would not discuss his deliberations.

"It was my decision and my decision alone," he said.

Sen. Sheldon Whitehouse (D., R.I.) asked the administrator about potential White House contacts several times, but Johnson essentially gave the same answer again and again: "I have routine contacts with various officials on a wide range of issues. . . . I value the ability to have candid discussions that are part of good government."

Afterward, Whitehouse compared Johnson's answers to evasive testimony given by former Attorney General Alberto R. Gonzales during the U.S. attorney scandal last year.

"Unfortunately, today Administrator Johnson stooped to that level," Whitehouse said.

During the hearing, the senator also pressed Johnson on his assertion that he had considered "a range of options" before he made his decision - from rejecting the waiver to approving it. The senator asked Johnson about the other options, the ones between the extremes.

When Johnson said he could not recall what those other options might be, Whitehouse replied: "On a matter of this significance, so recently decided, you can't remember some of the options you were asked to consider?"

Johnson replied: "I make my decisions and move on."

The EPA administrator has not yet released his detailed rationale for declining the California waiver. He said that document would be released by tomorrow.