During questioning by the national commission investigating the attacks, Tenet said the CIA might conceivably have been able to prevent the attacks, but they failed to "integrate all the data" and intelligence information was not fully shared.
"Maybe we would have had a chance. I can't predict to you one way or another," he said in testimony to the National Commission on Terrorist Attacks Upon the United States.
Commission staff issued a report that said CIA officials from the top down were under the impression before September 11 that the agency was only allowed to kill al-Qaida leader Usama bin Ladin as part of a covert operation to capture him.
"The idea that they (CIA's clandestine unit) are risk-averse, couldn't get the job done, weren't forward leaning. I'm sorry, I've heard those comments and I just categorically reject it," Tenet told the panel.
For the second day, the commission publicly questioned top Clinton and Bush administrations officials about why they did not take more forceful action against al-Qaida before the 2001 attacks on America that killed about 3000 people.
Former Democratic Senator Bob Kerrey expressed frustration that numerous military strikes were not conducted. "I don't see in the record any request for additional military operations."
He dismissed a secret Bush administration plan to tackle al-Qaida as woefully inadequate.
Repeatedly, commission members posed the same question: why did the agency fail to thwart the September 11 attacks?
"We didn't steal the secret that told us what the plot was, we didn't recruit the right people or technically collect the data, notwithstanding enormous effort to do so," Tenet said.
Commission members are asking
why attacks were not thwarted
"We didn't integrate all the data we had properly, and probably we had a lot of data that we didn't know about that if everybody'd known about maybe we would have had a chance. I can't predict to you one way or another."
A commission staff report on Tuesday said there were four times from late 1998 to 1999 when bin Ladin possibly could have been targeted, one was when he was near a hunting lodge in Afghanistan frequented by United Arab Emirates officials.
Tenet said it was unclear whether bin Ladin was there and another complicating factor was that "you might have wiped out half the royal family in the UAE in the process, which I'm sure entered into everybody's calculation in all this."
Bush plan criticised
Kerrey criticised the plan by the Bush administration for dealing with al-Qaida before September 11. "I was briefed this morning on that plan. And I would say, fortunately for the administration, it's classified because there's almost nothing in it."
The dramatic hearings have rattled the Bush administration, which has made its so-called war on terrorism the centrepiece of their re-election effort. Senior officials have been out in force defending their record.
"We didn't integrate all the data we had properly, and probably we had a lot of data that we didn't know about that if everybody'd known about maybe we would have had a chance. I can't predict to you one way or another"
The bipartisan commission, made up of five Democrats and five Republicans, is due to issue its final report on 26 July, at the height of the presidential campaign.
Top CIA officials, lawyers and operatives all believed that written authorisation from the Clinton White House, which was not changed in the Bush administration before September 11, only permitted killing bin Ladin if it happened during a capture operation, the commission said.
They also felt point-by-point instructions from Washington were too inflexible.
"Working-level CIA officers said they were frustrated by what they saw as the policy restraints of having to instruct their assets to mount a capture operation," said commission deputy executive director Chris Kojm.
Two veteran CIA counterterrorism officers who were deeply involved in bin Ladin issues "were so worried about an impending disaster that one of them told us that they considered resigning and going public with their concerns," the report by the commission's staff said. The report did not identify them.
Former counterterrorism coordinator Richard Clarke testified later at the hearing. Clarke, a senior adviser to Bush and the three previous administrations, created a stir this week by accusing the Bush administration of failing to recognize the urgency of the threat posed by bin Ladin's al-Qaida network.
Tenet said officials at the White House had grasped the sense of urgency he was communicating to them.