Ashcroft went on closed circuit television to address all 25,000 FBI employees, praising them for their successes but insisting that recent mistakes must never be repeated.
It was seen by some lawmen as a message from Ashcroft to the independent-minded bureau that, in effect, "Now you work for me," reports CBS News Correspondent Jim Stewart.
"Our challenge is not that we have problems," Ashcroft said of some recent FBI embarrassments. "Our challenge is how we respond to these problems."
Ashcroft said revelations that Robert Hanssen, a 25-year veteran agent, spied for Moscow for 15 years was but one of a string of difficulties that has beset the FBI.
"The problem of the Hanssen case joins the difficulty with the files in the McVeigh case in injuring the public trust," said Ashcroft, referring to the FBI's withholding documents in the Oklahoma City bombing case, which led to a delay in the execution of Timothy McVeigh.
"And these cases hearken back to earlier tragedies in Texas and Idaho," said Ashcroft, referring to deadly standoffs at the Branch Davidian compound in Waco, Texas, and with white a separatist at Ruby Ridge, Idaho.
Ashcroft has taken steps to crack down on the FBI after the series of blunders.
He gave a Justice Department watchdog agency broader authority to independently investigate allegations of misconduct at the FBI as is alleged in the case of nuclear weapons scientist Wen Ho Lee and ordered a top-to-bottom review of the bureau, including an independent study of management problems.
The FBI is also being investigated by the Justice Department's inspector general and by an independent panel headed by former CIA and FBI Director William Webster.
Polls show that more Americans have an unfavorable opinion of the nation's premiere crime-fighting agency. Members of Congress have long complained that the FBI tries to cover up its mistakes and does a poor job policing itself.
"There is a lack of openness and a lack of willingness to say, 'Well, we are a bureau that makes mistakes,'" said former Missouri Sen. John Danforth, who probed the bureau's performance at Waco.
The Bush administration has chosen veteran federal prosecutor Robert Mueller to replace Louis Freeh, who resigned as director last month after eight years of a 10-year term.
Mueller, the U.S. attorney in San Francisco and former head of the Justice Department's criminal division, has never worked at the FBI. He overhauled the San Francisco office, replacing prosecutors and stepping up prosecutions.
Ashcroft said Mueller "is a principled ad dedicated public servant. I know that under his direction we will triumph over the challenges ahead."
Unlike Freeh, who was infrequently seen at the Justice Department in the last years of the Clinton administration, Mueller is expected to be a team player for Ashcroft.
Other changes in top management at the bureau are expected as well.
Ashcroft praised the FBI for a long history of fighting bank robbers and terrorists, including the role FBI agents played in the investigation of the Pan Am 103 bombing and the conviction of five Cuban spies in Miami last month.
"You have served America well," said Ashcroft, addressing about 500 FBI employees, including division heads, special agents and technical and support personnel.
But he said new challenges have arisen and told agents to remember: "When people lose faith in their institutions they trust to enforce the law, justice is no longer possible."
"The call to duty beckons us," Ashcroft told agents. "It is a call to values. Without fidelity, without bravery, without integrity, we cannot succeed."
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