WASHINGTON ÷ Leaders of the FBI, CIA and National Security Agency told a congressional panel Tuesday what theyâve learned about the Sept. 11 terror attacks ÷ and about their own intelligence-gathering shortcomings.

FBI Director Robert Mueller, CIA Director George Tenet and the NSA director, Lt. Gen. Michael V. Hayden, appeared together behind closed doors before the joint inquiry of the House and Senate intelligence committees looking into the Sept. 11 attacks.

Senate Intelligence Committee chairman Bob Graham, D-Fla., and the committeeâs top Republican, Richard Shelby of Alabama, said after the session that mistakes have been made by all three agencies.

Shelby said, for example, that it would have been "very useful" if the NSA had translated certain communications.

Both said they do not know if the attacks could have been prevented even if the mistakes hadnât been made.

Graham also said the FBI and CIA now appear to be doing a better job communicating with each other, citing the arrest last month of Jose Padilla, an American suspected of plotting to detonate a dirty bomb.

Rep. Doug Bereuter, R-Neb., said through a spokeswoman that the questioning Tuesday was "establishing an important basis for examining deficiencies and failures pre-9/11, and making recommendations for improvements to protect our citizens."

The committees have spent most of the first two weeks of their inquiry being briefed on U.S. counterterrorism efforts since the 1980s and on the rise of Osama bin Ladenâs terrorist network.

The appearance of the three directors Tuesday allowed lawmakers to go to the heart of their inquiry: determining the facts surrounding Sept. 11, what intelligence and law enforcement problems existed before then and how they can be corrected.

Committee members have criticized the failure of the FBI and CIA to follow leads that potentially could have led them to the Sept. 11 hijackers before the attacks.

The problems include the refusal of FBI headquarters to allow an aggressive investigation of Zacarias Moussaoui after he was arrested a month before the attack. Moussaoui now faces trial as a conspirator of the hijackers and Osama bin Laden.

The FBI has also faced criticism for not following through on a memo by an agent in Phoenix urging checks of U.S. flight schools before Sept. 11 to see if they were training suspected terrorists.

Lawmakers also want to know why the CIA did not pursue information about two of the eventual hijackers after it placed them at a meeting with an important al-Qaida operative in early 2001 after the bombing of the USS Cole.

Speaking during a break in Tuesdayâs proceedings, Rep. Saxby Chambliss, R-Ga., said heâs seeking answers about "what appear to be very overt deficiencies" in the agenciesâ operations.

"How much of what we found out after the fact, if we had known before the fact, might have triggered somebodyâs mind to do some things differently?" he said.

A proposal submitted Tuesday by the White House to set up a Homeland Security Department calls for little change in the FBI and CIA, though it would require the agencies to submit intelligence information to the new department for analysis.

The three agency directors are expected to resume their appearances before the committees Wednesday. Mueller and Tenet are likely to return when the committees begin public hearings, scheduled for next week.