Mr. Bush told reporters that the White House is cooperating fully in the leak investigation. But he expressed doubt that persons who gave the information on the covert CIA officer will ever be found. In an exchange with journalists, he put it this way. "You tell me. How many sources have you had that [have] leaked information that you've exposed or has been exposed? Probably none," he said.

Mr. Bush was making the point that it is often difficult to track down who has passed on classified information to the news media. In part that is because reporters are reluctant to reveal their sources of information. Additionally, the President noted, there is a large number of people in the government who might have had access to the CIA officer's identity. "I don't know if we are going to find out the senior administration official [who leaked the name]. This is a large administration and we have many officials. I don't have any idea. I would like to," he said.

White House employees have been ordered to turn over all information related to the case for use by Justice Department investigators. As a 5:00 p.m. (2100 UTC) deadline approached, White House Spokesman Scott McClellan was asked by reporters about three specific members of the president's staff and their possible connection to the leak.

All three are senior advisers to the president. Mr. McClellan says chief political aide Karl Rove, Vice Presidential chief-of-staff Lewis Libby and the National Security Council's Elliot Abrams have denied any involvement. "Unfortunately in Washington, DC, at a time like this there are a lot of rumors and innuendo. There are unsubstantiated accusations that are made, and that is exactly what happened in the case of these three individuals," he said.

The disclosure of the identity of a covert CIA officer is considered a serious matter and can, depending on the nature of the officer's work, be a violation of U.S. law. But this case has taken on political overtones because the officer involved is the wife of a former American Ambassador who has been critical of the administration's case for war in Iraq. He says the identification of his wife as a CIA officer was White House punishment for his dissent.