Secretary of Defense Richard B. Cheney yesterday authorized activation of 72,500 more military reservists, taking the first step toward fulfilling President Bush's decision last week to deploy up to 200,000 additional U.S. troops in the Middle East.

Included in the new order was the first Pentagon authority under Operation Desert Shield to activate Army combat reserve units, defense officials said.

Cheney's decision more than doubles the number of National Guard and reserve personnel previously authorized for service with the operation, which is aimed at defending Saudi Arabia and possibly ousting Iraqi forces from Kuwait, officials said.

The Defense Department's new ceiling of 125,000 U.S. reservists who can be on active duty at one time represents a substantial jump from the 50,050 authorized after Iraq's Aug. 2 invasion of Kuwait. The Army, Air Force, Navy and Marine Corps are expected to respond soon with formal notices to the people and units being activated.

Officials said the new total is more than triple the number of reservists sent to participate in the Vietnam War, but well short of the 938,000 reservists activated for service in the Korean War. In theory, the services might not all reach their ceilings, although the new figures are considered rough approximations of eventual service intentions.

"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 in a statement released at the Pentagon.

The Army was given authority to activate 55,000 more reservists, while the Marine Corps can call up 12,000 and the Air Force 5,500. The Navy's authority to activate 3,700 more personnel for a total of 10,000, which Cheney granted Friday, remains unchanged.

Defense officials said Cheney has not decided whether to seek presidential approval to activate new combat reservists for up to 180 days, instead of the current renewable 90-day period. Noncombat reservists may be called up for 180 days under authority Bush granted for the first time Tuesday evening, officials said.

Defense officials said Cheney also gave the services' their first authority to extend the required 90-day stint for the 35,562 reservists already serving in Operation Desert Shield by as much as 90 more days. The first U.S. military unit becomes eligible for extension Nov. 22.

Cheney had previously authorized call-up of Navy, Air Force and Marine Corps reserve combat units, but only the Marines have used the opportunity.

Defense officials reiterated yesterday that all combat reservists may be required to undergo "refresher training" before being deployed to the Middle East.

Last week, the officials identified some National Guard units they expected to be sent to the Middle East as part of the additional deployment announced last week, including three large combat units from Georgia, Mississippi, and Louisiana.

A presidential order limits the total number of military reservists that may be activated at any one time to 200,000.