Democratic Sen. Patrick Leahy of Vermont 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.
Copyright 2013 The Associated Press.