Comey said he wasn't familiar with the details of the government's phone and Internet surveillance programs that recently became public, but he said that collecting that type of information can be "a valuable tool in counterterrorism."
"Folks don't understand that the FBI operates under a wide variety of constraints," Comey told the Senate Judiciary Committee, which is considering his nomination for FBI director. He added that when critics discount the oversight of federal judges and call them a rubber stamp, it "shows you don't have experience before them."
Committee Chairman Sen. Patrick Leahy, D-Vt., said the expansive scope of the surveillance programs raises the question of "when is enough enough?"
"Just because we have the ability to collect huge amounts of data doesn't mean that we should be doing so," Leahy said.
The senator asked Comey if he would be willing to work with legislators "to enact some common sense improvements to our surveillance laws," and Comey agreed to do that if confirmed as FBI director.
In the aftermath of the uproar over NSA spying, Leahy has introduced legislation that would improve privacy protections and strengthen oversight and transparency provisions in U.S. surveillance programs.
Comey spent 15 years as a federal prosecutor before serving in the George W. Bush administration, where he is best known for facing down the White House over a warrantless surveillance program. The White House made changes in the program when Comey and current FBI Director Robert Mueller threatened to resign.
Comey got a warm reception from the both Democrats and Republicans on the committee, who repeatedly referred to his independence in standing up to the Bush White House.
Civil liberties groups have nonetheless expressed concerns that Comey signed off on abusive CIA interrogation techniques for terrorist suspects during the Bush administration, when he was the Justice Department's No. 2 official.
Comey told the committee that he argued strongly within the Justice Department against the interrogation techniques, telling the attorney general that "this is wrong, this is awful" and insisting that his arguments be presented to the White House. But his objections were overruled.
The FBI Agents Association has told Leahy that it supports Comey's nomination.
The FBI is investigating Edward Snowden, the former NSA systems analyst who has admitted leaking details of the surveillance programs to the news media. Snowden is charged with two violations of the Espionage Act and theft of government property. To date, he has stayed out of the government's reach. He is believed to have been holed up in the transit area of Moscow's main airport since he suddenly appeared there on a plane from Hong Kong two weeks ago.
Civil liberties groups on Monday called on the government to release any reports by the Justice Department's inspector general on the collection of Americans' telephone records. If the inspector general has not previously reviewed the program, "We ask that it do so now," the groups said.
On a separate surveillance issue, Mueller told Congress last month that the FBI on rare occasions uses unmanned drones for domestic surveillance. The disclosure has prompted questions from members of Congress in both parties.
Meanwhile, the FBI has been conducting investigations of the Boston Marathon bombings and last year's attack at Benghazi, Libya, that killed four Americans. The Boston bombings probe resulted in a 30-count indictment against suspect Dzhokhar Tsarnaev. The Benghazi probe is ongoing.
After leaving the Justice Department, where he served as the agency's No. 2 official, Comey was senior vice president and general counsel at defense contractor Lockheed Martin. He later became general counsel at hedge fund Bridgewater Associates. His financial assets include $5.2 million in securities and a home in Westport, Conn., valued at $3 million, according to financial statements filed with the Senate.
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