For lawmakers examining intelligence failures leading up to the Sept. 11 attacks, few matters are as troubling as the case of the hijackers' meeting in Malaysia.

The CIA was aware that Khalid al-Mihdhar and Nawaf al-Hazmi had met in Malaysia in January 2000 with a man later determined to be an Al Qaeda leader. The FBI was informed of the meeting.

But the two men were not put on the State Department's watch list for denying visas until Aug. 23, 2001 — well after they entered the country and about three weeks before they helped hijack American Airlines Flight 77 and crash it into the Pentagon.

A congressional investigator, Eleanor Hill, was to tell House and Senate intelligence committee members Friday what U.S. authorities knew of the two hijackers, to what extent agencies shared information and why the men weren't stopped.

The chairman of the House Intelligence Committee, Rep. Porter Goss, R-Fla., told reporters Thursday that he was reserving judgment about whether the failure to stop al-Mihdhar and al-Hazmi was a clear-cut intelligence blunder.

``From what I have seen so far, there are questions that need to be asked to determine if there were mistakes,'' said Goss, a former CIA officer.

In written testimony at Thursday's hearings, Deputy Secretary of State Richard Armitage said that if intelligence agencies had notified the State Department sooner about the two men, ``it is reasonable to believe these two criminals would never have entered the country in the first place.''

``If we had had these two pieces to the jigsaw puzzle in advance, could we have seen the whole picture and prevented the attacks? Perhaps. But I don't believe that is a question we will be able to answer with any certainty,'' Armitage said.

After meeting behind closed doors since June, the committees are holding their third consecutive day of open hearings. On Wednesday, Hill, staff director for the joint inquiry, outlined numerous warnings of terrorist attacks received by intelligence agencies before Sept. 11. At least 12 warnings, dating back to the mid-1990s, involved the use of airplane as weapons.

At Thursday's hearing, the committees examined how top government officials from past and present administrations have used intelligence and to what extent they were aware of the threat Usama bin Laden posed.

``What we had was an emerging threat which we were slow to realize,'' Goss said after the hearing.

In his testimony, Armitage said officials ``knew that bin Laden had the means and the intent to attack Americans, both at home and abroad.''

``We did not know exactly what target Al Qaeda intended to attack and how and when,'' he said.

In other developments Thursday:

—CIA spokesman Bill Harlow issued a statement disputing some aspects of Hill's report, particularly suggestions that the agency did not devote significant resources to fighting terrorism before the attacks. CIA officials say, despite declining budgets, they directed substantial dollars and personnel to fighting terrorism, and stopped several attacks before they took place.

—Sen. Joseph Lieberman, D-Conn., and Sen. John McCain, R-Ariz., said they would try to form an independent commission to look into the Sept. 11 attacks. They are hoping to include the commission as part of the Senate bill creating a new Homeland Security Department.

Momentum for an independent commission has grown in recent months. Some lawmakers have questioned whether intelligence committees can complete a comprehensive investigation before their mandate ends in February.

The House has already voted to approve a commission as part of its intelligence authorization bill. The White House has opposed an independent commission, citing concerns about possible leaks and tying up officials involved in the fight against terrorism.