In closed-door briefings for members of Congress, Smith said officials from federal law enforcement and intelligence-gathering agencies disclosed that al Qaeda operatives have been exploring U.S. Web sites and probing the electronic infrastructure of American companies in search of ways to disable power and water supplies, disrupt phone service and damage other parts of the critical infrastructure.

Al Qaeda members seem especially interested in how they might disable the systems that provide electricity to California, Smith said. If it were to succeed, hospitals could be left powerless, causing patients to die, and commerce and much other activity would come to a halt, causing billions of dollars of economic damage.

Such a cyberattack could be used to dramatically increase the damage done by a physical attack, said Smith, who is chairman of the House Judiciary Committee's Crime, Terrorism and Homeland Security Subcommittee.