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.
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."