What high-level strategists here at the Rapid Deployment Force headquarters worry about most as they plan ways to fight in the Mideast oilfields is water.

Not beans. Not bullets. Water.

"Water will be equally as, if not more, important than ammunition in sustaining a force in the Middle East," said Brig. Gen. Carl Stiner, chief of staff of the Rapid Deployment Force and one of its experts on Persian Gulf countries, particularly Saudi Arabia.

"The last guy who had our problem," Stiner added, "was [Erwin] Rommel," commander of Germany's famed Afrika Korps in World War II.

In a place such as Saudi Arabia, with its 130-degree heat and scorching winds, each soldier would need 12 gallons of water a day to survive, U.S. planners figure. He would drink almost all of that, using a small amount of washing.

Each patient in a field hospital would need 40 gallons a day.

Each KC135 flying tanker plane would need 670 gallons and each B52 would need 300 gallons of pure water for injecting into the engines to increase power enough to take off with a full load.

"The Air Force needs such clean wate for its engines," Col. Dick Stephenson, RDF director of logistics, observed wryly, "that they ought to sign a contract with Perrier."

Water that is merely safe for drinking is not good enough for aircraft engines. It has to be distilled to clear it of contaminants.

Fighter plane and helicopter engines operating in the desert must be washed out frequently with a water-based solution to clean grit and dust off the turbine blades.

Logistical problems like these give Pentagon planners nightmares as they try to prepare a U.S. force for possible combat in the sands of East Africa or the Persian Gulf.

The RDF, President Carter's name for the collection of existing military units that have been designated to go to the Persian Gulf and East Africa if needed, cannot count on fanning out from bases near the trouble spot. The fighting units must bring everything with them. That includes water and associated gear.

The water problem means filling up valuable transport space with bulky purification equipment at a time the military is short of both air and sea lifts for moving other heavy stuff, such as tanks, from the United States and North Atlantic Treaty Organization countries to the Persian Gulf in a hurry.

Enlarging their already giant water problem, planners said, is the fact that they have recently been told they must have some water no warmer than about 70 degrees to treat GIs overcome by heat prostration.

"There're no 7-11 stores in those countries where you can get ice," said one planner, so the cool water requirement means refrigeration units must go along with RDF troops. These units, he added, must be able to withstand being hauled around the primitive countryside.

Assuming the problem of getting the water gear to the trouble spot is solved, planners then must deal with the "canteen problem." The GI canteen holds one quart, leaving the prospect of perhaps 100,000 GIs lining up for 48 refills every day to get the 12 gallons doctors insist they need.

"The numbers get awfully big," said Stephenson in sketching out the problem of distributing that much water to GIs spread out over the landscape thousands of miles from any American base. "That's an awful lot of garden hose."

Stiner said the soldiers' water requirement could be reduced if a decision were made to lay up during the day and fight only at night. But the enemy might have different ideas.

Besides that, planners here said, neither the Army nor the Marine Corps has a desert uniform to blend in with the landscape of the Persian Gulf. Green fatigues or jungle uniforms present a nice bright target against the desert brown.The Pentagon is moving to get a desert uniform made, they said, but just this one, seemingly easy, step will take up to three years to complete.

"That tells you how ready our industry is to turn out things we need in a hurry," said one military planner.

RDF leaders, given their mission to get forces ready to rush to 16 different countries in the Indian Ocean theater, cannot wait for long-term solutioins. So they are trying to solve the water problem with an estimated $200 million worth of quick fixes, including these:

Arranging to borrow, on short notice, four water purifies from the Interior Department. Each could process 175,000 gallons a day of seawater or whatever other water was available.

Buying six RODU (Reverse Osmosis Purification Units), which also could process 175,000 gallons a day.

Negotiating a contract for about 200 mobile RODU's each of which can cleanse 600 gallons of water an hour and can be hauled around the battlefield. But delivery of these units will take up to three years.

Recommending bigger canteens for those GIs and Marines most likely to be sent to the Persian Gulf area.

Souring the military's inventory for big containers that could be put near the trouble area, with everything from water tanker trucks to barges to large milk containers under consideration.

"Water is our No. 1 one problem in terms of support ability of the force," said Stephenson, the RDF's logistics chief here.

Although the RDF was originally billed as an outfit designed to respond to crises anywhere on the globe, Defense Secretary Harold Brown recently directed the RDF command to concentrate on three areas -- the Persian Gulf, the Middle East and the East African theater -- and has directed the Army to come up with a comprehensive plan for solving the water problem there.

The water problem has provoked fresh interest in a German general's postwar report entitled, "German Experiences in Desert Warfare During World War II."

The author, Generalmajor Alfred Toppe, wrote that "newly arrived units had low fighting power and many losses through sickness" when they first reached the African desert. The heat paralyzed the men's willpower and thus also their powers of resistance. . . .

"The problem of keeping water cool remained unsolved. . .," although Rommel's troops were able to get plenty of water because they remained near the coast, Toppe noted.

"If military operations had been carried out in the interior of the desert, water would undoubtedly have been the decisive factor which would have determined the strength of the troops and their radius of action."

Arabs historically have been fighting over and around water holes, planners here noted. But they add that the Arabs' armies have not had to fight big battles over long periods far from water sources -- a contingency for which the United States must plan.

Also, the water experts said that natives of many of the countries in the Persian Gulf area can get by on drinking water that would make an American GI sick. Moreover, said one specialist, the water in Saudi Arabia is so full of minerals that the type of filters used by the military in NATO countries will not remove enough minerals to make the water potable for Americans.

Both the Egyptians and the Israelis drank huge amounts of water and other liquids during their wars on the Sinai, planners noted. One said that many Egyptian troops ran out of water in the 1973 war because the distribution system broke down.

The Soviet military figures that three gallons of drinking water a day is enough for one of its troopers, specialists here said, but this does not count any water he can find for washing and cooking.

Also, the Soviet estimate does not take into account the special stresses of desert warfare, where outside temperatures hit 130 degrees and the heat inside an armored vehicle like a tank climbs to 180 degrees. A German study of the World War II Africa campaign said that heat "became unbearable" in combat when tank hatches had to be closed because of artillery fire and when the engines and ventilating system had to be shut off to save fuel.