Attorney General John D. Ashcroft recused himself yesterday from a politically charged investigation into the leak of an undercover CIA officer's identity, and his deputy announced the appointment of a special prosecutor in the case.

The probe into the disclosure of Valerie Plame's CIA affiliation to a newspaper columnist will be overseen by U.S. Attorney Patrick J. Fitzgerald of Chicago, who will act as a de facto attorney general on the case and will not be required to consult Ashcroft or other senior Justice Department officials while conducting the investigation, officials said.

Ashcroft's decision came abruptly after months of complaints from Democrats that the former Missouri senator's close ties to senior White House aides should disqualify him from overseeing the investigation, which has included FBI interviews of presidential adviser Karl Rove and other senior White House aides.

Justice Department officials declined to elaborate yesterday on what specifically prompted the change in course, and Ashcroft made no public comments.

Deputy Attorney General James B. Comey Jr., who announced the decisions at a news conference, said: "The issue surrounding the attorney general's recusal is not one of actual conflict of interest that arises normally when someone has a financial interest or something. The issue that he was concerned about was one of appearance. . . . That's the reason he decided, really in an abundance of caution, that he ought to step aside."

Comey also said: "It's fair to say that an accumulation of facts throughout the course of the investigation over the last several months has led us to this point." But he said officials could not provide details because "we don't want people that we might be interested in to know that we're interested in them. We also don't want to smear somebody who might be innocent and might not be charged."

It was Comey's decision to name a Justice Department official to lead the investigation rather than have an independent special counsel as many Democrats had demanded. He said Fitzgerald will operate more quickly and have fewer restrictions on his investigation than an outside prosecutor would.

Several outside legal experts said the decision signals that investigators may be narrowing their focus to one or more likely suspects, and that some of those people may have ties to Ashcroft. Officials said the recusal order applies to Ashcroft and his entire personal staff, which includes a number of longtime political aides from his days as a Republican senator.

"It is a reasonable surmise that they may be honing in on someone who is in a position connected with the administration itself, rather than a career civil servant," said Floyd Abrams, a New York media lawyer who has represented journalists in leak cases. "A political appointee, rather than a career civil servant, would be more likely to lead to consideration of a recusal."

The recusal marks the latest twist in the ongoing saga of Plame, whose identity as a CIA officer was disclosed by unidentified senior administration officials to columnist Robert Novak, who published her name on July 14. Willful disclosure of such information is a felony.

Plame is married to former ambassador Joseph C. Wilson IV, a prominent critic of the Bush administration's Iraq policies who concluded during a 2002 mission to Africa that there was little evidence that Saddam Hussein had sought uranium there. Wilson has said he believes his wife's identity was disclosed in retaliation for his public discussions of those findings.

In an interview yesterday, Wilson said that Ashcroft made the right decision to recuse himself. "You want an outcome that cannot be challenged or cannot be subject to the perception or accusation that there was a potential conflict of interest," he said.

Several leading Democrats, including Senate Minority Leader Thomas A. Daschle (D-S.D.), offered measured praise for the decision to name a special prosecutor, although most said it came too late in the three-month-old investigation. Sen. John F. Kerry (Mass.), a presidential candidate, assailed Ashcroft for "foot-dragging" and said that choosing a U.S. attorney to conduct the probe amounted to "a half-measure" that is "nowhere near good enough to restore public confidence."

Comey said that he and Ashcroft discussed the need for a recusal in the Plame case during the past week. Comey also said Fitzgerald, who is a close friend and former colleague, will enjoy greater independence than an outside special counsel, who would have been required to seek approvals from senior Justice Department officials on matters including media subpoenas and grants of immunity.

Fitzgerald will not have to do so, Comey said, and will be free to choose his own team of investigators or continue with those already in place. The Plame investigation has been led by career counterespionage prosecutor John Dion and has included a team of 12 FBI agents. Officials recently added a fourth prosecutor to the case, and the FBI has told people who have been interviewed that they may soon be called to testify before a grand jury.

Comey said his mandate to Fitzgerald was simple: "Follow the facts, wherever they lead, and do the right thing at all times,"

As U.S. attorney in Chicago, Fitzgerald has overseen the investigation of former Illinois governor George H. Ryan, who was indicted this month by a federal grand jury on charges of racketeering, mail and tax fraud, and lying to law enforcement officials. He previously spent 13 years as a prosecutor in the Southern District of New York, where he helped lead the prosecution of the 1998 U.S. embassy bombings and other terrorism cases. Comey described him as "Eliot Ness with a Harvard law degree and a sense of humor."

A spokeswoman for the U.S. attorney's office in Chicago said Fitzgerald was not granting interviews yesterday.

White House spokesman Trent Duffy said Bush, who is spending the week at his Texas ranch, was informed of the decision by his staff about an hour before Comey's appearance. "The White House was not consulted on the decision," he said, adding that the Justice Department notified the White House "as a courtesy." Comey said attorneys at the State Department, the Pentagon and the CIA were also notified.

Republican legal sources who have discussed the case with the White House and the Justice Department said the announcement will have the effect of providing political cover for the administration if no indictment is issued. One of these sources added that administration officials had expressed a desire to "depoliticize" the issue before the presidential campaign begins in earnest.

Allen reported from Crawford, Tex.

Attorney General John D. Ashcroft did not comment publicly about his decision in the case of the leak.