An attempted al Qaeda attack against the United States is a high possibility in the next 3 to 6 months, the nations' top intelligence chiefs testified today.
"An attempted attack, the priority is certain, I would say," Director of National Intelligence Dennis Blair told the Senate Select Committee on Intelligence.
CIA director Leon Panetta and FBI director Robert Mueller both told the committee they agreed with Blair's stark assessment, when asked by committee chairwoman Sen. Dianne Feinstein, D-Calif.
Blair and Panetta both said 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.
"We have made the complex, multiple-team attacks very difficult for al Qaeda to pull off," Blair said. "As we saw with the recent successful and attempted terrorist attacks, however, identifying individual terrorists, small groups with short histories using simple attack methods is a new degree of difficulty.
"We did not identify [Umar Farouk Abdulmutallab] before he boarded Northwest Flight 253 on Christmas Day. We should have," he said.
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 increasing 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.
Abdulmutallab Providing 'Useful Information'
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," he 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."
The threat warning comes amid an ongoing debate over how the Obama administration and the Justice Department handled the case of Abdulmutallab, accused of attempting to set off a bomb on Christmas Day on Northwest flight 253, and whether the case should have been handled in the criminal justice system.
Abdulmutallab is still being interrogated by FBI agents and is providing useful information to investigators, even though he was read his Miranda rights the day after the attempted bombing of flight 253, Mueller said.
The issue over providing Abdulmutallab the Miranda rights required in the criminal justice system has become a political issue among some Republican members in Congress, who assert that the Obama administration should have moved the terror suspect into the military tribunal process so he could be interrogated for intelligence.
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.
During questioning from Sen. Olympia Snowe, R-Maine, Mueller became agitated over the politicization of the case.
"I encourage you to look at what has happened since then," he 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."
Sources tell ABC News that FBI agents went to Nigeria and identified influential members of Abdulmuttallab's family who disagreed with what he did, and then brought them back to the United States to talk with him.
At Tuesday's hearing Blair said of the case, "The balance structure in the Mutallab case was understandable and balanced. We got good intelligence. We're getting more."
According to Justice Department and counterterrorism officials, the accused Al Qaeda in the Arabian Peninsula operative has provided some details about his handlers in Yemen and others who were training with him.
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.
A Justice Department spokesman declined to comment on the plea discussions, and Abdulmutallab's attorney Miriam Siefer did not reply to an email message.
FBI Explains Decision to Issue Abdulmutallab a Miranda Warning
Sen. Kit Bond, 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.
"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," the Missouri Republican 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.
Since the attempt to bring down flight 253, both Republicans and Democrats have questioned how the Justice Department handled the case, but Feinstein today said decisions should be made on a case-by-case basis.
"Candidly, my view is that the president should have the flexibility to make a determination based on the individual circumstances of the case -- the location of the terrorist activity, the location of the arrest, the nationality of the suspect, whether federal crimes or law of armed conflict have been violated," Feinstein said.
ABC News' Pierre Thomas contributed to this report.