Former top US officials staged an elaborate exercise on Tuesday to test the US response to a cyberattack which disables cellphone networks, slows Web traffic to a crawl and cripples the power grid.

Dubbed "Cyber ShockWave," the event was held in a Washington hotel room transformed for the day into the White House Situation Room, where the president and his advisers typically meet to address national emergencies.

Former president George W. Bush's Homeland Security chief Michael Chertoff played the role of National Security Advisor as the cabinet sought to respond to a nightmare scenario drawn up by former CIA director Michael Hayden.

As the "crisis" escalated, the officials discussed various actions including calling out the National Guard, nationalizing the utility companies and staging a retaliatory strike if the authors of the cyberattack become known.

"If this is an attack on the United States the president, as commander in chief, has the authority to use the full powers at his disposal," said former deputy attorney general Jamie Gorelick, in her role as attorney general.

"We're in good shape from a command-and-control standpoint," Charles Wald, a retired general acting as Secretary of Defense, reassured the cabinet.

"We can take action offensively if we know where to go," said Wald, former deputy commander of US European Command. "Problematically, we don't know where that is."

The exercise, which was filmed by CNN and will be broadcast at a later date, was organized by the Bipartisan Policy Center to "educate the public about our vulnerabilities," said Eileen McMenamin, BPC vice president of communications.

Three large video screens behind the participants displayed multi-color maps of the United States with a series of alarming updates and a fictional television network, "GNN," broadcast news reports on the cascading crisis.

The simulated cyberattack was spread through a free application for smartphones about "March Madness," the wildly popular annual US college basketball tournament.

The "March Madness" malware contained video footage of the Red Army although a security adviser warned this may be a "red herring" and whether the attack was launched by a state, terrorists or criminals could not be determined.

Launched from servers in Russia, it first crippled cellphone networks, then landlines, then the Internet and eventually the electricity grid in the entire eastern United States, exacerbated by a pair of bombings at power stations.

New York, Philadelphia and Washington were plunged into darkness, airline traffic was disrupted and the financial markets ground to a halt.

"This is a massive blow to the solar plexus of the economy," said "Treasury Secretary" Stephen Friedman, former director of the National Economic Council.

Joe Lockhart, former president Bill Clinton's press secretary, served as a counselor to the president, bringing a political perspective to the debate.

"We've got to bring the Hill leadership down to the White House," he said of the need to keep members of the US Congress informed.

National Security Adviser Chertoff peppered the cabinet with questions.

"If we were to shut a server down in Russia, would the Russians view that as an attack?" he asked. "If the attacker is either a state actor or a terrorist group what are our options for responding or retaliating?"

Speaking after the scenario was over, John Negroponte, the former Director of National Intelligence who played the role of Secretary of State, said it was all too real. "None of it struck me as particularly outlandish," he said.

Former deputy CIA director John McLaughlin, who was bumped up to Director of National Intelligence for the cyber game, said Al-Qaeda would clearly "like to carry out something like this but we don't know their capabilities."

"The Chinese and the Russians have the capability," added Fran Townsend, former president George W. Bush's one-time Homeland Security advisor, who was promoted to Homeland Security secretary for the simulation.

Wald, the Pentagon chief for a day, said, "I think the scenario we saw today is believable. I think we're preparing for it. I don't think we're as prepared as we should be."