Two Bush administration officials told lawmakers Thursday they knew before the Sept. 11 attacks that Usama bin Laden might attack Americans, but don't remember being warned that terrorists could fly passenger jets into buildings on U.S. soil.

"I don't recall any warning about the possibility of a mass casualty attack using civilian airliners," Deputy Defense Secretary Paul Wolfowitz told the House and Senate intelligence committees. The committees are holding a joint inquiry examining intelligence failures leading up to the attacks.

Wolfowitz and Deputy Secretary of State Richard Armitage appeared before the committees one day after the inquiry's staff director, Eleanor Hill, detailed many previously undisclosed warnings of possible terrorist attacks received by intelligence agencies before Sept. 11, 2001. At least 12 involved the use of airplanes as weapons.

On Thursday, 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 bin Laden posed.

"What we had was an emerging threat which we were slow to realize," Rep. Porter Goss, R-Fla., chairman of the House Intelligence Committee, told reporters after the hearings.

In his written 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.

Samuel Berger, who served as President Clinton's national security adviser, said he had heard of the possibility of airplanes being used as weapons as one of many possible threat scenarios.

"But I don't recall being presented with any specific threat information about an attack of this nature or any alert highlighting this threat or indicating it was any more likely than any other," he said.

CIA spokesman Bill Harlow issued a statement Thursday 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.

"We had no illusions about how hard that fight would be," Harlow said.

The agency doubled personnel in its Counterterrorism Center -- the nerve center for fighting terrorism -- between 1997 and the attacks, Harlow said. Before Sept. 11, the agency had 115 analysts looking at terrorism issues -- nearly three times what Hill's report states.

In addition, Harlow said the agency had a few dozen analysts in its center specifically monitoring Al Qaeda, plus another 200 field operatives assigned to counterterrorism duties, contrary to lower numbers in Hill's report. The center now has expanded to more than 800 people, more than twice what it had on Sept. 11.

The committees' inquiry is supposed to be completed by February, but with time running out in Congress, some committee members have expressed doubt it will be finished in time. Support has been building for an independent commission to investigate the attacks.

On Thursday, Sen. Joseph Lieberman, D-Conn., and Sen. John McCain, R-Ariz., said they will try to include an independent commission in legislation creating the Department of Homeland Security.

Lieberman said Wednesday's hearings showed the attacks "could have been prevented if we were doing everything we should have done and if we had had our guard up."

"I am confident that we have the support to adopt it," Lieberman told reporters. "When we get this commission up and working and [it] finishes its work, we can say with much more confidence than we can now that this will never happen again."

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

On Friday, lawmakers will hear from a CIA officer, an FBI agent and a former FBI official. Also, Hill will brief lawmakers on what staff have learned about the 19 hijackers. Much of that is expected to involve what was known about two hijackers, Khalid al-Mihdhar and Nawaf al-Hazmi, before the hijackings.

The CIA learned that al-Mihdhar and al-Hazmi had met in January 2000 with a person later determined to be an Al Qaeda leader in Malaysia, and informed the FBI of the meeting. But the two future hijackers were not put on the State Department's watch list for denying visas until three weeks before the attacks, when they were already in the United States.

Armitage said that the day after intelligence agencies informed the State Department about the two men, every consular office worldwide had been alerted.

"If we had had the information sooner, it is reasonable to believe these two criminals would never have entered the country in the first place," he said.

"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."