White House counsel Alberto R. Gonzales told the staff: "You must preserve all materials that might in any way be related to the department's investigation." Presumably that would include telephone logs, e-mails, notes and other documents.
The disclosure of the intelligence officer's identity by syndicated columnist Robert Novak came shortly after her husband, former Ambassador Joseph C. Wilson, undermined Mr. Bush's claim that Iraq had tried to buy uranium in Africa. In what turned out to be a major embarrassment, Mr. Bush later acknowledged he could not back up his statement.
Democrats contend the Bush Justice Department cannot fairly investigate the Bush White House and called for a special counsel to look into the matter.
Four Senate Democrats, including Minority Leader Tom Daschle, D-S.D., urged Attorney General John Ashcroft to appoint a person of "unquestioned independence and impartiality."
"We do not believe that this investigation of senior Bush administration officials ... can be conducted by the Justice Department because of the obvious and inherent conflicts of interests involved," said the letter, also signed by Sens. Carl Levin, D-Mich., Joseph Biden, D-Del. and Jay Rockefeller, D-W.Va.
Ashcroft declined a direct response to their calls for a special counsel, saying Tuesday that "because of an ongoing investigation of criminal violations, I will not be making any further comment at this time."
Later, a Justice Department official said "no options are closed" when asked if a special prosecutor has been ruled out. "We are not closing any legal doors," Justice Department official Mark Corallo said.
The investigation stems from a CIA complaint two months ago that one of its agent's identities had been disclosed. Justice gets about 50 such complaints from the CIA each year about leaks of classified information and few ever get beyond a preliminary investigation.
Speaking with reporters aboard Air Force One, White House spokesman Scott McClellan said Mr. Bush "has directed the White House to cooperate fully. The president wants to get to the bottom of this as much as anyone and believes it should be pursued to the fullest extent."
He added: "We welcome this investigation. No one wants to get to the bottom of this more than the president of the United States."
CBS News Legal analyst Andrew Cohen says the Justice Department will be looking for a paper trail and federal lawyers will want to interview White House staffers and others.
"Leak investigations are almost always very difficult ones, not just because reporters usually don't have to disclose the identities of their sources but also because the leaker typically covers his or her tracks," Cohen said.
On Monday, administration officials vigorously denied anyone at the White House leaked the CIA officer's identity.
"There's been nothing, absolutely nothing brought to our attention to suggest any White House involvement, and that includes the vice president's office as well," McClellan said.
In particular, McClellan said it was "ridiculous'' to suggest that Karl Rove, the president's top political operative, was involved, as Wilson once charged. "He wasn't involved," McClellan said of Rove. "The president knows he wasn't involved. ... It's simply not true."
Wilson backtracked Monday, saying Rove did not make the calls but either condoned or did not attempt to step the leak.
Novak wrote that he got the name from "two senior administration officials."
He said the CIA confirmed her role and "asked me not to use her name, but never indicated it would endanger her or anybody else."
The Washington Post reported that a White House official called six reporters with the agent's name.
The political impact could be significant, said CBS News Chief Washington Correspondent Bob Schieffer. "This is just bad news on all fronts for the president. There's no good in this to let this thing drag on for this administration."