"You must make the assumption that al Qaeda is in an execution phase and intends to strike us both here and overseas," Tenet said, noting recent attacks in Kuwait, Indonesia and off Yemen. "That's unambiguous as far as I'm concerned."
Tenet's comments came during an extraordinary session as he joined FBI Director Robert S. Mueller III and National Security Agency chief Lt. Gen. Michael Hayden to answer sharp questions from the House and Senate intelligence committees, in the culmination of five weeks of public hearings on missed warnings of the Sept. 11 attacks.
The hearing also led to new revelations regarding al Qaeda's planning for the Sept. 11 attacks. In a written report declassified Thursday, Tenet suggests that Osama bin Laden himself may have suggested the hijackers use large planes to strike the World Trade Center.
He also said al Qaeda will try to attack again.
"Based on what we have learned about the 11 September, an attempt to conduct another attack on U.S. soil is certain," he said.
Tenet said he was meeting later Thursday with Homeland Security Director Tom Ridge. He said Ridge has already taken defensive measures "in specific areas where the intelligence was most credible and in sectors where we're most worried about." He didn't identify them.
But he said the current situation is comparable with what existed in the United States in the summer before the Sept. 11 attacks.
"You must make the analytical judgment that the possibility exists that people are planning to attack you inside the United States — multiple simultaneous attacks. We are the enemy, we're the people they want to hurt inside this country," he said.
Homeland Security spokesman Gordon Johndroe said the nationwide alert level remains code yellow - "significant risk of terrorist attacks" - because officials do not have specific details on where and when an attack may occur. Yellow is the third-highest of five threat levels.
Animated and sometimes annoyed, Tenet offered his most detailed public accounting to date of what the CIA did to stop bin Laden's terrorist network before the Sept. 11 attacks. He said his agency has saved thousands of lives by successfully stopping terrorist attacks. But he also admitted some mistakes were made before Sept. 11.
Tenet said the CIA was convinced months before the Sept. 11 hijackings that Osama bin Laden was plotting to kill large numbers of Americans, but the intelligence available was "maddeningly short" of details that could have prevented the attack.
"The most ominous reporting hinting at something large was also the most vague," he said.
In weeks of hearings, the CIA and FBI have been criticized for not making fighting terrorism a high enough priority before the attacks and for failing to share information that might have led to the terrorist plot.
Tenet struck a defiant tone from the outset. Asked to limit his remarks to 10 minutes, he spoke for 50. When Sen. Bob Graham, chairman of the Senate Intelligence Committee, urged him to abbreviate his remarks, Tenet refused.
"I just have to say I've been waiting a year," he said.
Tenet highlighted agency successes, many of them long secret, including the thwarting of planned attacks in Yemen, Jordan and elsewhere in the Middle East.
Regarding criticism that the CIA should have given more warning that terrorists intended to use planes as weapons, Tenet said in seven years the agency received, and passed on, all 12 reports of such terrorist planning, even those from dubious sources. In comparison, counterterrorism officials received 20 times as many reports of potential car bombings, he said.
Tenet also said the CIA lost 18 percent of its budget and 16 percent of its personnel in the post-Cold War cutbacks. Training new intelligence officers to replace them will take time, he said.
But even before he spoke, Rep. Nancy Pelosi, the Democratic Whip, said "it's not enough to say we didn't have enough money or enough people. No one does. That's always the case. It's about establishing priorities."
Tenet clashed with the committees in an area where he admitted mistakes: the CIA's failure to put two future Sept. 11 hijackers on watch lists preventing their entry into the United States after they were first associated with al Qaeda, in early 2000. They weren't placed on the lists until a few weeks before the attacks.
Tenet said the CIA had alerted the FBI in January 2000 that one of the hijackers, Khalid al-Mihdhar, had a U.S. visa; the inquiry staff director said no evidence has been found showing the FBI was told about the visa.
After Tenet said that no one at the CIA apparently read a cable that said al-Mihdhar had flown to Los Angeles, Sen. Carl Levin, D-Mich., asked if that was a mistake.
"Yes. Of course. In hindsight," Tenet responded.
Mueller took a somewhat more conciliatory tone, saying the attacks highlighted weaknesses in counterterrorism efforts and that changes were made.
Hayden, in a rare public discussion of NSA operations, was blunt.
"I am not really helped by being reminded that I need more Arabic linguists or by someone second-guessing an obscure intercept sitting in our files that may make more sense today than it did two years ago," he said.
"What I really need you to do is to talk to your constituents and find out where the Americans want the line between security and liberty to be," he said.
Tenet also described some new evidence about the three years of planning of the Sept. 11 attacks.
He said Mohammed Atef, bin Laden's top deputy, studied the idea of bombing American airliners in 1996; Atef also chose the hijackers from young Arab men with no record of ties to terrorism. Atef was killed by a U.S. airstrike in Afghanistan last November.
He also hinted that the FBI's August 2001 arrest of Zacarias Moussaoui in Minnesota may have set the attacks in motion, noting all 19 hijackers bought their tickets within days after Moussoaui's arrest.
Moussaoui was arrested for immigration violations but later charged with conspiracy in connection with the Sept. 11 attacks. But U.S. officials have not laid out what they believe his precise role was to have been.
By John J. Lumpkin and Ken Guggenheim