Regional Outlook : Supplying America’s Desert Warriors : For millions of tons of food, weapons and spare parts, the Saudi road starts in St. Louis.

Over the past three weeks, the U.S. military has been carrying on the largest airlift in history to supply American troops in Saudi Arabia.

More than half a million tons of weapons, ammunition, food and other supplies--everything from spare tank tracks to peanut butter--already has moved over that 7,000-mile-long airborne “highway” since the operation began in early August.

Countless tons more--of uniforms, hot dogs, malaria drugs, gas masks and other items from the 4 million or so listed in the Federal Supply Catalog--will soon be en route, laden on ships and military aircraft based in Georgia, North Carolina and Texas.

The nerve center for the airlift is at Scott Air Force Base, a sprawling complex just outside St. Louis. There, the headquarters of the U.S. Transportation Command combines units from all three armed services into what is effectively the world’s largest moving company.

In a converted warehouse there, teams of supply specialists continuously monitor computer screens brightened with data transmitted from satellites positioned over the Atlantic. They provide the precise location of the two dozen or more ships now headed toward Saudi Arabia.

Not far away, in another room with floor-to-ceiling screens, other technicians track as many as 200 planes that may be flying toward the desert kingdom at any given moment.

Air Force Gen. Hansford T. Johnson, commander in chief of the U.S. Transportation Command, told reporters last week that the materiel now in Saudi Arabia or on its way is equivalent in weight to “400,000 Chevrolets.” So far, he says with some relief, “we’ve had no surprises.”

But keeping U.S. troops equipped to fight a war in the desert isn’t easy.

Take water, for example. In Saudi Arabia’s 130-degree heat, even the 20 gallons a day that’s usually cited as the maximum needed to keep a soldier fit for battle may not be enough. Each soldier should drink a quart every hour just to prevent dehydration, the experts say, andthat doesn’t count what’s needed for washing and personal hygiene.

As a result, the Pentagon has dispatched two barges with water-desalination plants to the gulf, each of them able to desalt and purify 125,000 gallons of water a day. The fresh water can then be trucked to the troops.

Another problem was created by the speed with which the buildup in Saudi Arabia had taken place. Although the Pentagon has done well in shipping existing stockpiles to the region, it has encountered at least a few snags.

For example, military supply officers had to tell three of the factories that make U.S. military uniforms to switch from manufacturing traditional green jungle fatigues to making sand-colored, desert-camouflage uniforms instead.

Besides buying 400,000 of the new uniforms, the Pentagon has ordered thousands of gallons of sand-colored paint for its tanks and other vehicles.

And then, of course, there are the dozens of amenities that accompany any modern-day army: Napoleon’s army traveled on its stomach and subsisted largely on bread. Today’s post exchanges--even in Riyadh--carry Frito Lay Doritos, Texas Pete Hot Sauce , Mennen Skin Bracer and Hormel Spam.

As it has in other crises, the Pentagon is relying heavily on commercial transportation to help do the job.

It has requisitioned and chartered 17 civilian passenger planes and 21 cargo planes to bolster its own force of nearly 300 C-5 and C-141 transports. It also has activated 38 of the 96 ships in its ready reserve fleet--vessels owned by the government and manned by civilians.

Initially, most of the supplies came from military depots and warehouses--mainly in Norfolk, Va., and Oakland--that maintain stockpiles of food and other items.

The Navy also keeps supply-laden ships pre-positioned in various waters. During the gulf crisis, it has called on vessels that have been anchored off Diego Garcia island, in the Indian Ocean.

Although all of the troops sent to Saudi Arabia were transported by air, 95% of the cargo is moving by sea. In World War II, the merchant marine played a major role in transporting troops and supplies, but in recent years, the U.S. shipping and shipbuilding industries have been in a state of decline. Military experts say the retrenchment of the merchant marine could seriously hamper U.S. logistics efforts if the conflict escalates.

One of the reasons that the supplying of Operation Desert Shield has been so smooth is that the mammoth oil-financed development projects of the gulf states and Saudi Arabia have included the construction of modern military bases, air facilities and deep-water ports.

Also, pilots making the 30-hour roundtrip journey to Saudi Arabia haven’t had to worry about flying over hostile territory.

Defense planners will not discuss how they would handle the logistics if the confrontation between U.S. and Iraqi forces erupts into a shooting war. But they assert that the effort should work smoothly as long as the air and sea corridors remain in friendly hands.

The organization that compiles and purchases the military’s shopping list is the Defense Personal Supply Support Center, located in an 11-square-block complex south of Philadelphia. The items are purchased through private contractors and shipped to depots in Pennsylvania, Utah, California and Tennessee.

During a normal year, the agency spends $3.5 billion on food, clothing and medical supplies for the military. Over the past three weeks alone, it has spent $600 million responding to the gulf crisis, a spokesman said.

On the center’s recent shopping list:

* 1.8 million pounds of hamburger. Cost: $2 million.

* 318,000 chemical protective suits. Cost: $21.7 million.

* 115,000 anti-fragmentation vests. Cost: $28.9 million.

* 600,000 tubes of lip ointment. Cost: $99,000 for the load.

The agency also has purchased 115,000 pairs of goggles designed to protect the wearer from sun, wind and dust, 1.2 million cartons of “ultra-high-temperature” milk and 230,000 cans of foot powder.