Mr. Mueller pointed out that the 9,200 national security letters involved only 3,500 individuals.

"The only thing they can't do is say that they were the recipient of a national security letter."

The military's frequent use of national security letters has sometimes caused concerns from the businesses receiving them, a counterterrorism official said.

But the expanded use of national security letters has allowed the Pentagon and the intelligence agency to collect records on their own.

We went to the university with a national security letter.

They declined to produce the documents pursuant to a national security letter.

The report found that the use of national security letters has exploded in recent years.

Unlike search warrants, national security letters do not need to be approved by a judge.

The use of national security letters since the September 2001 attacks has been a hotly debated domestic intelligence issue.

The final bill also gave recipients of national security letters the explicit right to consult lawyers.