Gonzales said the government would have to determine that a conversation involved terrorism before listening in, the Washington Post reported.
"I'm not going to rule it out," Gonzales said, responding to a question from Rep. Adam Schiff, D-Calif., on the extent of the president's power to order monitoring of communications that are entirely within the United States.
In the past, President George W. Bush, Gonzales and others in the administration have emphasized that monitoring by the National Security Agency ordered after Sept. 11, 2001, has involved only communications where at least one party was outside the country.
Gonzales, in his testimony, hinted there may be other surveillance programs that remain secret. He was talking about reports of disputes within the administration.
"They did not relate to the program the president disclosed," Gonzales said. "They related to something else and I can't get into that."