Mr. Arkin, in the online supplement to his book (codenames.org/documents.html ), says the contingency plan, called JCS Conplan 0300-97, calls for "special-mission units in extra-legal missions to combat terrorism in the United States" based on top-secret orders that are managed by the military's Joint Staff. Mr. Arkin provided The New York Times with briefing slides prepared by the Northern Command, detailing the plan and outlining the military's preparations for the inauguration. Three senior Defense Department and Bush administration officials confirmed the existence of the plan and mission, but disputed Mr. Arkin's characterization of the mission as "extra-legal."

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