The Pentagon has established a new military headquarters whose mission is to defend the nation's capital and to assist civil authorities in responding to a terrorist attack here.

The Joint Forces Headquarters for the National Capital Region (search) is based at Fort McNair, a small Army post in Washington on the banks of the Anacostia River whose fortifications did not stop the British from invading in 1814 and burning the White House and Capitol.

The idea of the new Joint Forces Headquarters is not to fend off foreign armies but to prevent if possible — and respond to, if not — surprise attack by terrorists using nuclear, chemical, biological or other unconventional means, Army Maj. Gen. Galen B. Jackson said Monday.

"There are vulnerabilities in the nation's capital," he said without being specific.

One of those vulnerabilities is the proximity of the White House, the Capitol and other government buildings to commercial air traffic, as shown by the Sept. 11, 2001 attack on the Pentagon.

Jackson is commander of the new headquarters. The deputy commander is Rear Adm. Jan Gaudio, who also is commandant of the Naval District of Washington, which provides support services to naval installations within a 100 mile radius of the Pentagon.

Jackson and Gaudio briefed reporters Monday about the arrangement and the new operations center, where they can monitor a broad range of information from the FBI and other government agencies.

The new outfit also has a mobile command center, a $3.2 million truck chocked full of computer, telephone, TV and other communications to enable Jackson or others to travel to the scene of an emergency and remain in touch with the secretary of defense as well as other agencies.

The idea is to improve the military's ability to coordinate a post-attack response, as well as complicate a potential attacker's planning by varying the placement and visibility of security measures, Jackson said.

Before Sept. 11, 2001, the military organizations in Washington focused largely on ceremonial activities like a presidential inauguration, as well as installation management.

Now they are being asked to focus also on homeland defense. Even the U.S. Army Band, for example, is now trained to provide administrative medical support in the event of an attack.

There is a wide range of military forces based in the Washington area, but none in large numbers. The Army has its 3rd Infantry Regiment, the famed "Old Guard" best known for sentry duty at the Tomb of the Unknowns at Arlington National Cemetery, as well as the Army's 12th Aviation Battalion, which has 18 Black Hawk helicopters based at Fort Belvoir, Va., south of the capital.

Also in the area is an Army engineer company with special training in rescuing people from collapsed buildings, as well as a bomb disposal unit at McNair that is trained to respond to nuclear, chemical, conventional and improvised explosive incidents anywhere in the capital region.

Jackson's organization is subordinate to U.S. Northern Command (search), a military headquarters in Colorado set up after the Sept. 11 attacks to coordinate land defense of the United States. Air defense is the responsibility of the North American Aerospace Defense Command (search).

The only area of the country with a joint force headquarters devoted specifically to its defense is Washington.

A ceremony Wednesday will mark the official activation of Joint Forces Headquarters for the National Capital Region, but it already has been put to work several times in recent months. It set up a joint task force to respond to the discovery of the deadly poison ricin last February on Capitol Hill, for example.