"Today it is my honor to call this humble son of Texas the 80th Attorney General of the United States," Mr. Bush said of his former White House counsel, who becomes the first Hispanic to serve as the nation's top law enforcement officer.
"With Al's leadership, the Department of Justice will defend the security of all Americans and the liberty of all Americans," the president said.
Mr. Bush used the event to call on Congress to renew all provisions of the USA Patriot Act this year. "We must not allow the passage of time or the illusion of safety to weaken our resolve in this new war," he said.
The president also argued that the Senate must give his nominees for the federal bench up-or-down votes without delay to fill vacancies in the courts.
The Patriot Act, passed in the wake of the Sept. 11 terrorist attacks, bolstered FBI surveillance and law-enforcement powers in terror cases, increased use of material witness warrants to hold suspects incommunicado for months, and allowed secret proceedings in immigration cases.
Civil liberties groups and privacy advocates lambasted the law because they said it undermines freedom. But Mr. Bush said the act "has been vital to our success in tracking terrorists and disrupting their plans." He noted that many key elements of the law are set to expire at the end of the year and said Congress must act quickly to renew it.
The Patriot Act was pushed by Gonzales' predecessor, John Ashcroft, who was in the audience as Gonzales took his oath from Supreme Court Justice Sandra Day O'Connor. Mr. Bush lauded Ashcroft's tireless efforts to make America safer as he oversaw a drop in violent crime besides his counterterrorism work.
Gonzales, who served as White House counsel during the last four years, said he would be a part of Mr. Bush's team but his first allegiance will be to the Constitution.
"I am confident that in the days and years ahead we in the department will work together tirelessly to address terrorism and other threats to our nation and to confront injustice with integrity and devotion to our highest ideals," Gonzales said.
Gonzales was confirmed by the Senate on a 60-36 vote on Feb. 3 despite Democratic complaints that he helped craft questionable U.S. policies on the treatment of foreign prisoners.
Democrats also complained that Gonzales, as a longtime friend and associate of Mr. Bush's, was too beholden to the president to be attorney general.
Gonzales was officially sworn-in shortly after the Senate vote.
During his confirmation hearing, some Democrats charged that Gonzales' January 2002 memo as White House counsel led to the abuse of suspected terrorists in Iraq and Afghanistan. The memo argued that the fight against terrorism "renders obsolete Geneva's strict limitations on questioning of enemy prisoners and renders quaint some of its provisions."
Pressed by senators on the issue, Gonzales defended the memo and that the treaty's protections did not extend to al Qaeda and other suspected terrorists, but declared, "Torture and abuse will not be tolerated by this administration.,"
He told senators that as attorney general he would "ensure the Department of Justice aggressively pursues those responsible for such abhorrent actions."