And if a senior administration official were involved, McClellan added, "they would no longer be in this administration ... at a minimum -- at a minimum."
A Justice Department spokesman, Mark Corallo, said the department is conducting a "preliminary investigation" into the alleged leak to determine whether a full-blown investigation is warranted.
Corallo said the probe was being jointly handled by the FBI and career attorneys in the counterespionage section of the department's criminal division.
Novak said the CIA asked him not to disclose Plame's name, "but never indicated it would endanger her or anybody else," and that he was led to believe that she was "an analyst, not a spy, not a covert operative, and not in charge of undercover operatives."
Novak was wrong on those accounts, according to the CIA. "We wouldn't file a crimes report" if the case didn't involve an agent undercover, a U.S. official said.
A 1982 federal law specifically prohibits the unauthorized disclosure of the identity of a clandestine intelligence officer. Nobody has been prosecuted under the law, said Steven Aftergood, director of the project on government secrecy at the Federation of American Scientists.
U.S. intelligence officials declined to discuss details of the case, but said exposing an operative's identity is a serious breach with unpredictable consequences. It not only deprives the operative of being able to work undercover in the future, but threatens to expose her sources, some of whom may be risking their lives to share secrets with the CIA. Outing an officer also places in jeopardy any CIA operative who replaces her in her overseas "cover," often a diplomatic post at a U.S. embassy.
The official said the agency is obligated under federal law to refer leaks of classified information to the Justice Department. The agency refers about 50 such leaks a year, the official said.
Congress passed the 1982 law after a former CIA operative, Philip Agee, launched a campaign in the 1970s to expose sensitive CIA operations and to identify CIA officers around the world. Some intelligence experts believe Agee's high-profile campaign helped create the climate that led to the 1975 assassination of Richard Welch, the CIA station chief in Athens, Greece, by an ultra-leftist group.
Agee was stripped of his U.S. citizenship in 1979, and he was last known to be running a travel agency in Havana, Cuba. But he stopped publicly identifying U.S. intelligence operatives after the law was passed, Aftergood said.
"People leak things day in and day out about government officials, their spouses and their pets," Aftergood said. But he said the Wilson case "is a unique circumstance ... and the proposed motivation is unusually sordid."
"The idea is, as far as I can understand it, that Wilson would be discomfited somehow by the exposure of his wife," Aftergood said. "It's a particularly nasty attempt to silence a critic, if that is what happened here."
Only one person has been convicted of leaking classified information to the media, which is also illegal but falls under a different statute than the law protecting identities of intelligence agents.
Navy intelligence analyst Samuel L. Morison provided satellite photographs of Soviet installations to Jane's Defence Weekly in 1984. He was pardoned by President Clinton in 2001.
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Times staff writers Bob Drogin, Edwin Chen, Richard Schmitt and Johanna Neuman contributed to this report.
