Lawmakers serving on the House-Senate panel probing pre-Sept. 11 intelligence breakdowns have been asked to submit to lie-detector tests to learn the source of a leak, according to reports Friday.

"Lie-detector tests are a standard element of FBI investigations and they are meant to eliminate people from suspicion," an official said, speaking on condition of anonymity. "They are always voluntary."

Sen. Richard Shelby, R-Ala., said he refused to take the test and he's not alone.

"I don't know who among us would take a lie-detector test," said Shelby, the ranking Republican on the Senate panel. "First of all, they're not even admissible in court and second of all, the leadership (of both parties) have told us not to do that."

The FBI investigation into leaks about intelligence failures at the CIA, FBI and National Security Agency was requested by Sen. Bob Graham, D-Fla., chairman of the Senate Intelligence Committee, and Rep. Porter J. Goss, R-Fla., chairman of the House Intelligence Committee, after Vice President Dick Cheney criticized the panel for allowing sensitive information to leak out.

At issue were reports, which actually began appearing before the special committee was formed, about Arabic communications intercepts picked up by the NSA the day before the Sept. 11 attacks, but not translated until two days later. Those translations revealed messages such as "The match is about to begin" and "Tomorrow is zero hour."

White House spokesman Ari Fleischer said after the leak appeared in newspapers that the level of detail was "alarmingly specific" and undermined national security.

The FBI investigation has encompassed agents interviewing nearly all of the panel's 37 lawmakers as well as polygraph tests for some 60 employees of the NSA, CIA, Defense Department and Congress.

But according to The Washington Post, most of the members on the panel have refused to be polygraphed themselves, citing separation of powers between the legislative and executive branches as well as the unreliability of the exams.

The refusal marks a real turnaround from the days immediately following the investigation request, when Goss said that the members would "cooperate with the FBI in any way possible," even if it meant submitting to polygraphs.

One lawmaker described the tension that has evolved between Congress and the FBI since the investigation began.

"It's a very akward situation for the FBI and members of Congress, and again I think it's a little silly," said Sen. Chuck Hagel, R-Neb., a member of the committee. "I've said before if you've got to go around and give your members of Congress polygraph tests, then we've got a more serious problem than just leaking sensitive information out. If we can't trust our nation's leadership with sensitive information, then we ought to go back and start all over again.

The Senate's top Republican expressed little sympathy for the members of the panel, however, and savored the irony of the lawmakers' predicament.

"I do think it's ironic that an investigation has been requested into this particular leak that you are referring to by the bipartisan leaders of the Ethics Committee. And then when the investigation goes forward, at the request of the committee themselves, then people start complaining about, 'Oh, my goodness, they're asking us questions,'" said Senate Minority Leader Trent Lott, R-Miss.

The House-Senate panel is expected to finish its investigation into pre-Sept. 11 intelligence failures before the end of the year. However, some lawmakers have discussed creating an independent commission to look at intelligence leaks.

The White House has opposed such a move, citing the leaks themselves as reason why an independent unit should not be organized.

Fox News' James Rosen and the Associated Press contributed to this report.