The U.S. attorney in Chicago, Patrick J. Fitzgerald, will take over the investigation and report to James Comey, who is Ashcroft's top deputy. Comey, in an announcement at the Justice Department, called the new top prosecutor "Elliot Ness with a Harvard law degree and a sense of humor."
"He has the power and authority to make whatever prosecutorial judgment he needs," Comey said.
This will not be Fitzgerald's first high-profile investigation. He oversaw the investigation of former Illinois Gov. George Ryan, a Republican who was indicted this month on 22 counts of corruption, including taking free vacations, tax fraud, lying to federal agents and skimming cash out of his own campaign fund. Ryan pleaded innocent a week ago.
Sen. Charles Schumer, D-N.Y., one of the main critics of how the Bush administration has handled the leak investigation, praised the announcement.
"It is not everything we asked for but it comes darn close," Schumer said in a statement. "And tonight, the American people can, as a result, feel more assured that there will be a full and thorough investigation, no matter where it leads."
Comey said Ashcroft's decision to recuse himself was not based on an actual conflict of interest but on the appearance of a possible conflict.
"The attorney general in an abundance of caution believed that his recusal was appropriate based on the totality of the circumstances and the facts and evidence developed at this stage of the investigation," Comey said. "I agree with that judgment."
Comey did not say exactly what evidence necessitated the recusal.
Comey said he considered bringing in an outside counsel but decided Fitzgerald was the "perfect man for this job" because of his experience in national security matters. He also said by choosing somebody from within the Justice Department, there would be no delay in continuing the investigation.
Fitzgerald can keep the career prosecutors and FBI agents who have handled the work so far, Comey said. Unlike an outside counsel, Fitzgerald can make prosecution decisions without having to first inform Comey, who is acting as the attorney general for this investigation.
Comey and Assistant Attorney General Chris Wray will supervise the investigation. "It is not in the public interest to move this matter entirely from the Department of Justice," Comey said.
Comey said he had a simple mandate for Fitzgerald: "Follow the facts wherever they lead and do the right thing all of the time."
Investigators want to know who leaked the name of Valerie Plame, an undercover CIA officer, to syndicated columnist Robert Novak in July. Plame is married to former Ambassador Joseph C. Wilson, who has said he believes his wife's identity was disclosed to discredit his assertions that the Bush administration exaggerated Iraq's nuclear capabilities to build the case for war.
The leaker could be charged with a felony if identified.
The FBI has interviewed more than three dozen Bush administration officials, including political adviser Karl Rove and press secretary Scott McClellan.
The interviews have extended beyond the White House to other government agencies. The Defense and State departments and the CIA itself also are part of the probe.
The focus, however, remains on the White House, two law enforcement officials said on condition of anonymity. While the initial, informal interviews have yielded no major breaks, the FBI is satisfied that the dozen agents assigned to the probe are making progress and have not encountered any stalling tactics, the officials said Thursday.
So far, no grand jury subpoenas have been issued, they said.
Wilson said he had no idea why Ashcroft chose to recuse himself now. He speculated that Ashcroft, who has long ties to members of the president's staff, simply wanted to make sure that any findings at the end of the investigation are not tainted by even the suspicion of conflict of interest.
"I would have no idea whether a report has emerged that led him to recuse himself," Wilson said in a telephone interview Tuesday. "I have always said, as some senators have argued, that the administration needed to take a good hard look at this."
He declined to express satisfaction over Ashcroft's recusal.
"It's not a question of whether I'm happy about it," he said. "The crime that was committed was not committed against me or my wife, but against my country. It's the country that's the victim in this."