FROM the NATIONAL RESPONSE PLAN
III. Roles and Responsibilities
When State resources and capabilities are overwhelmed, Governors may request Federal assistance under a Presidential disaster or emergency declaration.
Summarized below are the responsibilities of the Governor, Local Chief Executive Officer, and Tribal Chief Executive Officer.
Governor
As a State's chief executive, the Governor is responsible for the public safety and welfare of the people of that State or territory.
The Governor:
Is responsible for coordinating State resources to address the full spectrum of actions to prevent, prepare for, respond to, and recover from incidents in an all-hazards context to include terrorism, natural disasters, accidents, and other contingencies;
Under certain emergency conditions, typically has police powers to make, amend, and rescind orders and regulations;
Provides leadership and plays a key role in communicating to the public and in helping people, businesses, and organizations cope with the consequences of any type of declared emergency within State jurisdiction;
Encourages participation in mutual aid and implements authorities for the State to enter into mutual aid agreements with other States, tribes, and territories to facilitate resource-sharing;
Is the Commander-in-Chief of State military forces (National Guard when in State Active Duty or Title 32 Status and the authorized State militias); and
Requests Federal assistance when it becomes clear that State or tribal capabilities will be insufficient or have been exceeded or exhausted.
Federal Government
Department of Homeland Security
The Homeland Security Act of 2002 established DHS to prevent terrorist attacks within the United States; reduce the vulnerability of the United States to terrorism, natural disasters, and other emergencies; and minimize the damage and assist in the recovery from terrorist attacks, natural disasters, and other emergencies. The act also designates DHS as a focal point regarding natural and manmade crises and emergency planning.
Secretary of Homeland Security
Pursuant to HSPD-5, the Secretary of Homeland Security is responsible for coordinating Federal operations within the United States to prepare for, respond to, and recover from terrorist attacks, major disasters, and other emergencies. HSPD-5 further designates the Secretary of Homeland Security as the principal Federal official for domestic incident management. In this role, the Secretary is also responsible for coordinating Federal resources utilized in response to or recovery from terrorist attacks, major disasters, or other emergencies if and when any of the following four conditions applies:
(1) a Federal department or agency acting under its own authority has requested DHS assistance;
(2) the resources of State and local authorities are overwhelmed and Federal assistance has been requested;
(3) more than one Federal department or agency has become substantially involved in responding to the incident; or
(4) the Secretary has been directed to assume incident management responsibilities by the President.
Department of Defense (DOD)
DOD has significant resources that may be available to
support the Federal response to an Incident of National Significance.
Secretary of Defense
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The Secretary of Defense shall provide defense support of civil authorities for domestic incidents as directed by the President or when consistent with military readiness and appropriate under the circumstances and the law. The Secretary of Defense shall retain command of military forces providing civil support.
http://www.dhs.gov/interweb/assetlibrary/NRPbaseplan.pdf