WASHINGTON (AP) _ Secretary of Defense Dick Cheney on Wednesday authorized the military services to call up 72,500 more reservists and National Guard members because of the situation in the Persian Gulf.

His action brings to 125,000 the number of Army, Navy, Air Force and Marine Corps reservists who can be on active duty. The limit had been 48,800 before Friday and 52,500 before Wednesday's announcement.

His action had been expected in the wake of President Bush's decision last week to order an additional 200,000 troops to the gulf region, in addition to the approximately 230,000 already there.

The president said the expansion was necessary to enable the United States to go on the offensive.

The administration had previously said that the mission of the troops, sent to Saudi Arabia after Iraq invaded neighboring Kuwait on Aug. 2, was defensive.

Cheney's action raises the call-up ceilings from 25,000 to 80,000 for the Army, from 14,500 to 20,000 for the Air Force and from 3,000 to 15,000 for the Marine Corps.

Last Friday, the ceiling for naval reservists was raised from 6,300 to 10,000.

Cheney also extended to the Army the authority, previously granted to the other services, to call reserve combat units to duty if needed. The earlier orders had limited the Army to support units.

Combat units may be ordered to undergo refresher training before they are sent overseas, the Pentagon said.

''Today's armed forces are designed with combat support and combat service support built into the reserves,'' Cheney said. ''As we increase the deployment of active duty forces, we must also call upon more members of the National Guard and Reserve to get the supporting forces we need,'' Cheney said.

Earlier Wednesday, Bush extended the tour of active duty for the reservists from 90 to 180 days. The original order in August had specified 90 days, subject to an additional 90 by presidential action.

Congress has passed legislation permitting combat reserves to be called up for an additional 180 days by presidential action, but Cheney said the Defense Department has not yet asked the president for such authority.

Since Cheney's original order on Aug. 23, there have been 35,562 reservists called to active duty. They include 24,524 in the Army, 4,616 in the Navy, 5,278 in the Air Force and 1,144 by the Marine Corps. In addition, the Coast Guard has called up 511.

Also on Wednesday, the Navy announced it was activating 17 medical, public affairs and construction units of the Naval Reserve in 13 states.

That announcement said 62 reservists are being called to active duty from the 17 units. The activation of a reserve unit may not involve the entire unit, the Navy said.

The units, with their missions, are:

4th Light Armored Vehicle Company A, Santa Ana, Calif., medical support for Marine Corp.

4th Medical Detachment, 4th Tank Battalion, San Diego, Calif., medical support for Marine Corps.

4th Marine Air Wing, Medical Marine Air Group 46, San Diego, medical support for the Marine Corps.

4th Medical Detachment, 3rd Air Naval Gunfire Liaison Company, Long Beach, Calif., medical support for the Marine Corps.

Office of Information Detachment 1118, Aurora, Colo., public affairs support.

4th Marine Air Wing, Medical Marine Air Group 41, Marietta, Ga., medical support for the Marine Corps.

4th Medical Detachment, 4th Combat Engineering Battalion, Baltimore, medical support for the Marine Corps.

1st Reserve Naval Construction Brigade, Gulfport, Miss., construction support.

Office of Information Detachment 1018, Kansas City, Mo., public affairs support.

4th Force Reconnaissance Company, Reno, Nev., medical support for the Marine Corps.

4th Medical Detachment, 2/25 Detachment F, New Rochelle, N.Y., medical support for the Marine Corps.

Office of Information Detachment 411, Oklahoma City, public affairs support.

Atlantic Fleet Imaging Unit 193, Willow Grove, Pa., public affairs support.

Office of Information Detachment 310, Houston, Texas, public affairs support.

4th Medical Detachment, Norfolk, Va., medical support for Marine Corps.

Office of Information Detachment 713, Milwaukee, public affairs support.