President Bush has decided to call up tens of thousands of Army, Air Force and Navy reservists to support the U.S. military deployment to the Middle East and final details of the call-up will be worked out by the Pentagon in the days ahead, administration officials said yesterday.

An Army official said as many as 80,000 Army reservists could be called to active duty based on the Army's recommendations that went to the president. Some notices to reservists could go out next week. The other services' contribution to a reserve call-up would be substantially smaller.

Defense Secretary Richard B. Cheney, meeting with the chiefs of staff of the four military services before his departure for the Middle East yesterday, told the military leadership that a call-up plan had been approved by the president, a military official said.

Pentagon officials said Cheney has asked Bush to order the activation of up to 200,000 National Guard and reserve troops.

En route to visit leaders of Saudi Arabia, Egypt, Bahrain, Oman and the United Arab Emirates, Cheney said he believes "the breadth of the American commitment was more than they {the Saudis} had expected" and described the U.S. mission as "long-term," staff writer Molly Moore, traveling with Cheney, reported.

"I do not know when we will be able to come home," Cheney said, adding that he could not rule out the possibility that U.S. forces would still be in Saudi Arabia in 1992.

While he refused to disclose the number of U.S. troops already in the nation, he said, "I'd like to have more of them before I will be comfortable with the situation."

In addition to reviewing U.S. troops in the region, Cheney is expected to discuss the possibility of more U.S. arms sales with the leaders of the nations he is visiting.

Bob Hall, deputy Pentagon spokesman, said the Pentagon paperwork on the reserve call-up was on its way to Kennebunkport, Maine, for the president's signature and a formal announcement would be made by the White House.

Full details of the call-up will be worked out over the next several weeks as Army, Navy and Air Force officials set priorities for special units they need in Saudi Arabia quickly to support the tens of thousands of troops on the ground or arriving in daily transport flights.

The Army has recommended the call-up of at least one reserve brigade from the Georgia National Guard representing about 3,500 reservists. This is the "round-out" brigade to the 24th Infantry (Mechanized) Division at Fort Stewart, Ga. The two active brigades of this division already have been dispatched to the Persian Gulf.

Among the specialized units the Army had identified for call-up are: stevedores for ship cargo loading and handling, drivers and transport specialists, ammunition handlers, quartermaster and water desalination plant experts, cooks and bakers, laundry operators, petroleum pipeline specialists, communications experts in radio, microwave and satellite communications, military intelligence photo interpreters and psychological warfare specialists. Some reserves could be assigned to bases in the United States to fill in for active duty units sent abroad.

The decision to make a substantial call-up is further evidence of the extent of the Bush administration's military commitment to the confrontation with Iraq. The administration has not spelled out the size of the force it intends to assemble. But Pentagon sources have said it could grow to 200,000 troops or more.

Over the last decade, the military has taken more and more combat support units out of its active duty forces and put them into the reserve as an economy measure. Ideally, these reserves are partially or fully trained for wartime tasks and provide the military with its "surge" capacity to mobilize on short notice for a large conflict.

The conflict with Iraq in the Persian Gulf will test this system, officials said yesterday.

The decision to consider a call-up of the reserves was made shortly after Bush ordered troops into Saudi Arabia 10 days ago. Gen. H. Norman Schwarzkopf, the commander in chief of the U.S. Central Command, which is in charge of the Persian Gulf deployment, informed the Joint Chiefs of Staff of the force structure he would need on the ground and asked each service to support it.

"This is the way we designed the Army and we need them {reserves} now," one Army official said.

The military chiefs have met almost daily this week to work on recommendations for Cheney and the president on a general call-up.

Officials were not clear about whether the president's decision restricted the call-up in any way. But based on the recommendations that went to Bush, "some of those units could go tomorrow," an Army official said. "Some will take time to train, but if we don't start tomorrow, they are going to miss the war."

An example of the need for special combat support units was in the area of Army laundry operations. One official said that if reserve laundry and cleaning units get to Saudi Arabia immediately, the arriving forces still will not have clean laundry for three weeks.

In addition, the Pentagon activated the Civil Reserve Air Fleet, which consists of commercial planes from 29 airlines, for use in carrying cargo and troops in military operations in the Persian Gulf. The order mandates that 16 civilian airlines provide up to 38 aircraft within 24 hours in response to the gulf crisis.

Since the beginning of Operation Desert Shield, the military has used civilian aircraft on a voluntary basis to move troops and equipment, but the airlift has so overtaxed military planes that the Pentagon, for the first time in the 38 years that the program has existed, has exercised its contractual right to use commercial planes, officials said.

Tyler reported from Washington, Balz from Kennebunkport.