"I think it's a bad idea. I think that it's an infringement constitutionally on the legislative branch. And I don't think there's much support for it," said Senate Majority Leader Tom Daschle, D-S.D.
The Republican leader, Sen. Trent Lott of Mississippi, agreed the "separation of powers is certainly a difficult one" but that lawmakers should heed Bush administration warnings about leaks.
"I have to say that the thing for members of Congress to do is to keep their mouths shut when it involves sensitive and classified information," said Lott, who appeared with Daschle in a televised interview.
The FBI investigation was requested by congressional intelligence committees after news organizations reported details of Arabic conversations intercepted by the National Security Agency on Sept. 10. The conversations made vague references to an impending attack on the United States.
FBI officials have said polygraph tests are a standard investigative technique and are always voluntary.