WASHINGTON, 17 August 2003 — Terrorism sprang to mind when the lights suddenly went out for millions of Americans and Canadians. But fears of Al-Qaeda strikes on the vulnerable power grid were unrealized, federal officials quickly determined.

Had it been an actual attack, it is unlikely the terrorists would have met their goals. There was little evidence of panic, violence or threats to public health and civil order.

Thanks to backup power supplies — probably last upgraded before Y2K — the vital institutions kept the lights on. Hospitals stayed open and jail doors stayed closed.

Still, the speed and scope of the outage were staggering. Twenty power plants shut down as a safety mechanism and were slowly being reintegrated into the grid. Safeguards prevented it from spreading further. The cause was unclear.

New York City was slowly getting its power back early Friday. But some in Michigan and elsewhere may have to wait days, officials said. As the scope of the power loss became apparent, the Homeland Security Department readied its emergency response teams to aid any state or city that needed them. No call came, department officials said. They credited local authorities with being prepared for problems of this nature in the post-Sept. 11 environment.

“I think this situation indicates that technology is imperfect and at times will fail,” said Brian Roehrkasse, a department spokesman. “This indicates the importance of having in place protections to guard our critical infrastructure as well as crisis plans for when the infrastructure becomes inoperable.”

Because the power grid is everywhere, it is vulnerable to attacks that can leave many people without power for a time. Every power line, every transformer, every transfer station cannot be defended. But because it is so large, attacks that would turn off the power, and leave it off for more than a few days, are difficult to envision.

The outage showed how much modern civilization relies on keeping the electricity flowing. “It shows us we have tied together so many systems to build a high quality life, and that creates its own vulnerabilities,” said James Gilmore, the former Virginia governor who now is chairman of a terrorism panel formed by Congress.

New Mexico Gov. Bill Richardson, energy secretary during the Clinton administration, said the blackout underscored the need for Congress to require national standards for the reliability of the electric power system.

“In my view we’re the world’s greatest superpower but we have a Third World electricity grid,” Richardson said. “We have antiquated transmission lines. We have an overloaded system that has not had any new investments and we don’t have mandatory reliability standards on utilities, which caused this problem.”

National standards, Richardson said, “are needed to prevent utilities from having more power than they can absorb. It’s as simple as that.” Larry Brown, an official with Edison Electric Institute who advises the government on electric grid vulnerabilities, said there were three reasons that better facilities have not been built: The cost, environmental opposition and the unwillingness of communities to locate such facilities near homes.

“Things like this can wake people up to the reality that society relies on electricity, and expects electricity to be reliable. But reliability depends on facilities,” he said.