WASHINGTON — A major cyber attack somewhere in the United States is becoming increasingly possible, top government intelligence officials said Thursday, warning that an assault on America’s power-grid system “”represents the battleground for the future.””

The officials, speaking at a special hearing on Capitol Hill, also said that while al-Qaida has been diminished after nine years of the U.S. war on terror, more foreign groups have risen up, increasing concerns among U.S. authorities that one of them may eventually get their hands on a nuclear device.

“”I don’t think there’s any question but that this is a real national security threat that we have to pay attention to,”” CIA director Leon Panetta said of a cyber attack in this country. “”The Internet, the cyber-arena … this is a vastly growing area of information that can be used and abused in a number of ways.””

With that in mind, he told the House Permanent Select Committee on Intelligence, “”When it comes to national security, I think this represents the battleground for the future. I’ve often said that I think the potential for the next Pearl Harbor could very well be a cyber attack.””

Panetta said terrorists are determined to find a way to hack into the power grid system in the United States, which he said, “”brings down the financial system, brings down our government systems. You could paralyze this country. And I think it’s a real potential, and that’s the thing we have to really pay attention to.””

He noted that extremists in Iran, Russia and China are developing “”a significant capacity”” to stage such an attack, and that already “”hundreds of thousands”” of attempts are being made to sneak into national security networks.

“”We’ve got to develop not only a defense against that,”” he said, “”but we’ve got to put our assets in places where we can provide sufficient warning that these attacks are coming.””

On the threat from nuclear, chemical and biological weapons, Michael E. Leiter, director of the National Counterterrorism Center, said extremists are trying to gain control of nuclear weapons in Pakistan, and in fact “”remain committed to obtaining all types of weapons of mass destruction.””

James Clapper, director of the Office of National Intelligence, was asked to elaborate. All he would say was, “”Our assessment is that the nuclear weapons in Pakistan are secure. And that’s probably all we should say about that in public.””

The officials said other terrorist chieftains in Yemen and around the Arabian Peninsula also want the weapons, and that their “”intent remains high.””

But they said the intelligence community in the United States remains committed as well.

“”In dealing with terrorism, in dealing with al-Qaida, and dealing with jihad,”” Panetta said, “”we’re going directly at them. And we try to do everything we can to make sure that we disable their leadership, disable their command and control, disable their operations.””