WASHINGTON -- FBI director Robert Mueller yesterday staunchly defended a pair of controversial government surveillance programs, telling Congress that leaks about them harms national security.

In his final appearance as director before the House Judiciary Committee, Mueller said that "every time that we have a leak like this -- and if you follow it up and you look at the intelligence afterwards -- they are looking at the ways around it."

"One of my problems is that we're going to . . . lose our ability to get their communications. We are going to be exceptionally vulnerable," he declared.

Last week's revelations that the National Security Agency is collecting millions of U.S. phone records and digital communications have touched off a fiery national debate. The Obama administration, in its efforts to thwart terrorism, has overstepped proper bounds by using intrusive surveillance methods whose scope is stunning, several lawmakers suggested.

The admitted leaker of the NSA's secrets, 29-year-old contractor Edward Snowden, is the subject of an ongoing criminal investigation, Mueller testified.

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Mueller said the Foreign Intelligence Surveillance Court has approved the programs and they have been conducted in compliance with U.S. law and with oversight from Congress.

Rep. John Conyers, the committee's ranking Democrat, said "it's my fear that we are on the verge of becoming a surveillance state."

In defending the programs, Mueller called attention to the run-up to the Sept. 11, 2001, terrorist attacks, saying that if the surveillance efforts had been in place then, they might have uncovered the hijackers' plot.

"If we had had this program, that opportunity would have been there," Mueller said.

"I am not persuaded that that makes it OK to collect every call," Conyers replied.