WASHINGTON -- The director of the National Security Agency says U.S. surveillance programs have disrupted or helped disrupt dozens of terrorist attacks.

NSA director Keith Alexander defended the programs at a Senate hearing on Wednesday.

Democratic Sen. Patrick Leahy says some details of two cases have been declassified. He pressed Alexander for numbers on other incidents.

Leahy says the intelligence community believes that these surveillance programs are critical, but he adds that he thinks they should not be made permanent and that Congress should be able to review and debate them periodically.

A former contractor, Edward Snowden, leaked information on the programs last week.