FBI officials are reviewing travel records from Africa to determine if terror operatives trained in Yemen have already made their way to the United States as top intelligence chiefs warned that an attempted al Qaeda attack against the United States is a high possibility in the next three to six months.
"We judge that al Qaeda maintains its intent to attack the homeland -- preferably with a largescale operation that would cause mass casualties, harm the U.S. economy or both," National Intelligence Director Dennis Blair wrote in his annual threat assessment for the House Permanent Select Committee on Intelligence today.
Blair told the Senate Select Committee on Intelligence Tuesday that an attempted attack "is certain."
CIA Director Leon Panetta and FBI Director Robert Mueller told the Senate committee they agreed with Blair's stark assessment, explaining that it is becoming more difficult to identify the threat posed by an evolving al Qaeda, which has become more reliant on its regional terror networks to conduct attacks.
Some of the intelligence about purported attacks has come from alleged Christmas Day bomber Umar Farouk Abdulmutallab, who, officials said, is providing "useful, actionable information" to the FBI.
Intelligence from the suspect and other sources indicate that there are other people like Abdulmutallab who were trained in Yemen and not all killed by the U.S. raids there in December, ABC News consultant and former counterterrorism official Richard Clarke said.
"There are people like him who we don't know their names, we don't know what they look like, but they probably don't look like our stereotypical view of an Arab terrorist," Clarke said on "Good Morning America" today. "We may not even know what country they're from -- they may be British, they may even be American -- who are out there and that probably means there will be another attempt."
Despite the sobering assessment from the nation's top intelligence chiefs, Clarke said, another attempt does not necessarily mean there will be another successful attack.
"We shouldn't panic here," he said. "CIA directors always say this once a year in an annual threat briefing. And they always predict there's going to be another attempt. Another attempt does not mean another successful attack, so we shouldn't all head to our bunkers."
Blair today shot down ideas that threats of homegrown terror may be on the rise.
"It is clea r... that a sophisticated, organized threat from radicalized individuals and groups in the United States comparable to traditional homegrown threats in other countries has not emerged," he wrote in his testimony. "Indeed, the elements most conducive to the development of an entrenched terrorist presence -- leadership, a secure operating environment, trained operatives, and a well-developed support base -- have been lacking to date in the United States or, where they have been nascent, have been interrupted by law enforcement authorities."
Blair did warn House members of "malicious cyberactivity" by terrorists.
"The United States confronts a dangerous combination of known and unknown vulnerabilities, strong and rapidly expanding adversary capabilities, and a lack of comprehensive threat awareness," Blair wrote in his threat assessment. "Malicious cyberactivity is occurring on an unprecedented scale with extraordinary sophistication."
The attacks, he said, could disable financial systems, an assessment with which Clarke agreed.
"It's already come," Clarke said, citing the recent cyberattack on Google, allegedly conducted by the Chinese, a charge that the government denied.
"Every day, major corporations in this country lose their intellectual property, their corporate secrets, without even knowing it, to successful Chinese hacks. This is the real big threat because it takes away our economic advantage," Clarke said.
Umar Farouk Abdulmutallab Providing 'Actionable' Information
Abdulmutallab's family was critical in trying to persuade him to cooperate. FBI agents secretly went to Nigeria and identified influential members of Abdulmutallab's family who disagreed with what he had done, and then brought them back to the United States to talk with him, sources told ABC News.
Abdulmutallab is providing information about his al Qaeda handlers in Yemen and others who were training with him, officials said. The Nigerian national faces life in prison, not the death penalty, and, administration officials said, his cooperation appears to be driven by the power of his family's persuasion.
The family was "instrumental in gaining Mr. Abdulmutallab's cooperation," a senior administration official said. The information Abdulmutallab is sharing has been described by other officials as fresh and actionable.
"It has been very successful," the official said, "as far as gaining his cooperation that will allow us then to follow up on that information."
He said the intelligence gained "has been disseminated throughout the intelligence community."
Mueller said Tuesday that Abdulmutallab was read his Miranda rights the day after the attempted bombing of Flight 253, a point assailed by Republicans.
"It makes no sense to capture someone fresh off the battlefield and within 50 minutes, read them their Miranda rights and lose all the intelligence they possess to help us win this war," Sen. Lindsey Graham, R-S.C., said at a news conference Tuesday.
GOP leaders also say that the Obama administration should have moved the terror suspect into the military tribunal process so he could be interrogated for intelligence.
Despite the criticism, experts said, the FBI has been relatively successful at getting Abdulmutallab to provide information.
"FBI is very good at getting these people to talk, and despite all the partisan sniping about what the FBI has done, they are the professionals and they have been much more successful than the previous attempts at torturing people and trying to get them to give information that way," Clarke said. "The FBI does it right."
Justice Department officials have said that Abdulmutallab decided to stop speaking with federal investigators the day after the attempted bombing, even before he was given a Miranda warning by FBI agents.
"I encourage you to look at what has happened since then," Mueller said. "And it is a continuum in which, over a period of time, we have been successful in obtaining intelligence not just on day one, but day two, day three, day four, day five and down the road. And so I encourage you to look at it as a continuum as opposed to looking at is as a snapshot of what happened on one day."
The discussions between Abdulmutallab, his lawyers and federal investigators began last week as Justice Department officials explored the possibility of offering Abdulmutallab a plea deal in exchange for his cooperation and information he has about the terror network.
Sen. Kit Bond, R-Mo., the ranking Republican on the Intelligence Committee told Blair he disagreed with the conclusion that the case was handled properly because the suspect has been giving investigators information.
Law enforcement officials said they read Abdulmutallab his rights only after he underwent medical treatment and then refused to talk. They say the fact that he is now cooperating shows they are effective.
"There should be a decision made after consultation with the relevant agencies and the intelligence community when an enemy combatant comes in, before the Department of Justice gives the order to Mirandize him," Bond said. "He's an enemy combatant and the decision ought to be made by the intelligence -- with the participation of the intelligence community."
The decision to issue a Miranda warning to Abdulmutallab was reached by the FBI's chief of counterterrorism in conjunction with Justice Department attorneys, Mueller said.
Challenge Identifying Potential Terrorists
Intelligence officials say they have stepped up efforts to thwart al Qaeda attacks but that it is becoming more difficult to identify the threat posed by an evolving al Qaeda, which has become more reliant on its regional terror networks to conduct attacks.
"Counterterrorism efforts against al Qaeda have put the organization in one of its most difficult positions since the early days of Operation Enduring Freedom in late 2001," Blair told lawmakers today. "However, while these efforts have slowed the pace of anti-U.S. planning and hindered progress on new external operations, they have not been sufficient to stop them."
Much of the urgent concern about another possible attack is fueled by the near-miss bombing attempt on Christmas day.
"We did not identify [Abdulmutallab] before he boarded Northwest Flight 253 on Christmas Day. We should have," Blair testified Tuesday.
Panetta shared Blair's assessment of the al Qaeda threat as something that has changed since the terror attacks of Sept. 11, 2001, when four coordinated groups of terrorists hijacked separate airliners to crash them in New York and Washington.
"My greatest concern and what keeps me awake at night is that al Qaeda and its terrorist allies and affiliates could very well attack the United States in our homeland," the CIA director said. "The biggest threat I see is not so much that we face another attack similar to 9/11. I think the greater threat is that al Qaeda is adapting their methods in ways that oftentimes make it difficult to detect."
Al Qaeda has found new safe havens and established "regional nodes in places like Yemen and Somalia, the Maghreb [North Africa] and others," he said.
Panetta also warned that he is becoming increasingly concerned about threats from "lone wolf" terrorists who act on their own without any central planning from an established terror network such as al Qaeda.
He cited the case of Ft. Hood shooter Maj. Nidal Hasan as one such case of a "lone wolf" terrorist.
"So it's the lone-wolf strategy that I think we have to pay attention to as a threat to this country," Panetta said. "We are being aggressive at going after this threat. We've expanded our human intelligence. We are engaging with our liaison partners in other countries to try to track these kinds of threats."
ABC News' Jake Tapper contributed to this report.