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Defense Secretary Leon E. Panetta warned Thursday that the United States was facing the possibility of a “cyber-Pearl Harbor” and was increasingly vulnerable to foreign computer hackers who could dismantle the nation’s power grid, transportation system, financial networks and government, report Elisabeth Bumiller and Thom Shanker in Friday’s New York Times.

In a speech at the Intrepid Sea, Air and Space Museum on the Hudson River in New York, Mr. Panetta painted a dire picture of how such an attack on the United States might unfold. He said he was reacting to increasing aggressiveness and technological advances by the nation’s adversaries, which officials identified as China, Russia, Iran and militant groups.

Defense officials said Mr. Panetta was responding to a recent wave of cyberattacks on large American financial institutions. He also cited an attack in August on the state oil company Saudi Aramco, which infected and made useless more than 30,000 computers.

But Pentagon officials acknowledged that Mr. Panetta was also pushing for legislation on Capitol Hill. That legislation would require new standards at critical private-sector infrastructure facilities — like power plants, water treatment facilities and gas pipelines — where a computer breach could cause significant casualties or economic damage.

Mr. Panetta’s comments, his most extensive to date on cyberwarfare, also sought to increase the level of public debate about the Defense Department’s growing capacity not only to defend but also to carry out attacks over computer networks. Even so, he carefully avoided using the words “offense” or “offensive” in the context of American cyberwarfare, instead defining the Pentagon’s capabilities as “action to defend the nation.”