Speaking at Mukasey's ceremonial oath-taking, Mr. Bush said the retired federal judge "will bring clear purpose and resolve" to the agency.
"As he embarks on his new responsibilities, Michael Mukasey has my complete trust and confidence," Mr. Bush told a packed ceremony at the Justice Department's Great Hall. Agency employees filled the hall and lined the balcony to watch their new boss take the ceremonial oath from Supreme Court Chief Justice John Roberts.
With a pointed smile at the applauding crowd, Mr. Bush added: "And he's going to have the trust and confidence of the men and women of the Department of Justice."
Mr. Bush also promised to announce on Thursday nominees to fill some of the dozen vacant senior leadership jobs in the department, which has been in a state of upheaval since a series of controversies - including the dismissals of federal prosecutors - led to the resignation of Attorney General Alberto Gonzales.
When Mr. Bush praised Gonzales as a man of integrity and decency, Justice Department employees responded with sustained applause. It got even louder moments later after Mukasey took the oath, formally ending the Gonzales chapter in the agency's history.
Mukasey, who also worked in the Justice Department early in his career as a trial prosecutor in New York, said "it's great to be back."
He promised to make sure the Justice Department follows an "unswerving allegiance" to the law and the Constitution.
Though he was officially sworn in last week to begin work, Mukasey said he did not feel he had become the attorney general until taking the oath in front of his employees.
The ceremonial swearing-in of Mukasey took place in plain sight of the 12 1/2 foot statue of the bare-breasted 'Spirit of Justice,' reports CBS News White House correspondent Mark Knoller.
"My job involves not only an oath, but also a pledge, which I now give you," Mukasey told the 110,000 Justice employees nationwide, some of whom watched on the department's internal TV system.
"And that is to use all of the strength of mind and body that I have to help you to continue to protect the freedom and the security of the people of this country, and their civil rights and liberties, through the neutral and evenhanded application of the Constitution and the laws enacted under it."
He said he would "ask myself in every decision I make whether it helps you to do that, to take the counsel not only of my own insights but also of yours, and to pray that I can help give you the leadership you deserve."