The deployment of tens of thousands of troops and thousands of tons of equipment to Saudi Arabia is imposing tremendous strains on the U.S. military, requiring the Air Force to divert more than 70 percent of its transport planes worldwide and the Navy to activate seldom-used reserve ships for the massive operation.

Pentagon officials, who have long complained that the military does not have enough airplanes and ships to move substantial forces quickly to trouble spots across the globe, say the Operation Desert Shield deployment is highlighting those shortcomings.

After almost a week of frenetic airlift activity, the Air Force has moved to the region only a fraction of the combat, communications, and support equipment it needs, according to Pentagon officials. The service's transports are carrying primarily weapons and equipment. To get around the shortage of military transports, most of the troops are being flown to the Middle East on commercial craft chartered by the military.

"If Saddam Hussein had crossed the border that first night . . . we could have used 100 percent of what we've got, but wouldn't have been able to get the force there we would have needed," said Brig. Gen. Bob L. Mitchell, the Air Force's deputy director of plans.

While the military has deployed tens of thousands of troops, dozens of fighter planes and planeloads of tanks, helicopters and other equipment to Saudi Arabia, most of the heavy armor and other mechanized equipment needed for ground defenses has only begun to be loaded on ships. Military officials said it could be 30 to 45 days before adequate ground forces are in place.

"We're not in the defensive position we'd like to be in," said Mitchell, adding that forces now in Saudi Arabia could adequately deter an attack by the Iraqis, but "we would not have enough forces to do what we would like to do."

In addition to the nightmarish logistics of moving large numbers of troops and vast quantities of equipment to the region quickly, the military faces the equally difficult task of keeping troops supplied and trained in a hostile desert environment.

Air Force officials estimate that a squadron of 24 F-15 fighter planes flying two sorties a day would need a total of 3.5 million gallons of fuel per month. They said they computed the total on the basis of three hours of flying time per plane each day, with each plane gulping 1,653 gallons of fuel per hour. The 1,500 to 2,000 engineers, technicians, armorers, maintenance personnel and other workers needed to keep the squadron operating at a remote base would use roughly 1 million gallons of water -- 20 gallons a day for each person -- and would eat 100 tons of food per month.

That force of jets and people is only a fraction of the hundreds of aircraft and up to 200,000 troops that military officials have said could be dispatched to Saudi Arabia by autumn.

The Navy has deployed its entire fleet of eight fast sealift ships to get tanks and other heavy equipment to the Middle East from the United States. It is dispatching to the Persian Gulf most of the 22 other cargo ships it has positioned around the world with stores of equipment, ammunition and supplies for the Marines, Army and Air Force and is now dipping into its reserve cargo forces faster than ever before, according to officials of the Military Sealift Command.

The reserve ships, called the Ready Reserve Force, are aging vessels that were cast off by commercial companies as uneconomical. The Navy refitted them to carry tanks, trucks and other large equipment. At least 12 of the Navy's 96 reserve ships, operated by civilian mariners, have been activated, according to officials.

Among the first troops dispatched to Saudi Arabia last week were hundreds of engineering and support personnel who set up support facilities for troops and weapons at remote locations, according to Brig. Gen. James E. McCarthy, the Air Force's deputy director of engineering and services.

While the military prepositions tons of supplies, foodstuffs and equipment at strategic locations worldwide in the event it is needed for combat, the Middle East locations were set up primarily in anticipation of aggression by Iran, rather than Iraq, creating some problems, McCarthy said.

Pentagon officials also said that the threat of Iraqi use of chemical weapons has exposed a long-existing deficiency in special gear for chemical warfare for U.S. forces. The deployment has required that the military raid the equipment and medical stores of units that will not be deployed to the Middle East in order to provide enough gas masks, protective suits and other supplies for the troops sent to Saudi Arabia.

The Air Force also is taxing its refueling tanker fleet, which is critical to the Saudi operations, officials said. Fighter and bomber pilots may need to refuel their planes as often as eight to ten times during the long flight between the United States and Saudi Arabia, Air Force officials said.

According to Air Force pilot Maj. Jeff Smith, a KC-135 tanker may be needed to accompany every two to four fighter planes sent across the Atlantic Ocean to the Middle East. The larger KC-10s can carry enough fuel for up to six fighters or bombers on the transatlantic leg, he said.

Air Force officials said they expect the experiences of Operation Desert Shield will bolster their arguments for the new C-17 transport plane, which can carry more and heavier equipment and use shorter runway space that existing aircraft. The C-17 program, beset with delays and cost overruns, was reduced by Defense Secretary Richard B. Cheney as part of budget-cutting efforts for the next several fiscal years.

Officials said logistical problems on the ground in Saudi Arabia are complicated further by air traffic snarls created when so many huge jet transports use the limited number of runways at civilian Saudi airports and remote military airstrips. Air traffic controllers have had to stagger landings and takeoffs, further slowing the unloading of critical equipment and increasing the turnaround time to get the planes headed back to U.S. bases.

Military officials say the brutal desert weather already is taking a toll on troops in the region. Some are experiencing heat rashes and dehydration in temperatures that are routinely above 100 degrees. Some pilots, with limited training in flying in a desert environment, have suffered from occasional vertigo because of difficulty in distinguishing between the sand and the sky on distant horizons, officials said.

Special air filters designed to keep sand out of electronic equipment are already in high demand, and mobile radars and computers have malfunctioned because printed circuits have swelled in the extreme heat, one official said.

Staff writer R. Jeffrey Smith contributed to this report.