ENTERING the U.S. Army base at Mannheim is like going home. Driving through the gate, you leave behind the medieval architecture of a German city on the banks of the Rhine and enter Middle America. You find yourself in a small city that might be in Colorado, Ohio or Alabama, complete with supermarkets and split-level homes, swimming pools and schools, bowling alleys and barber shops, bars and barbecue pits, barking dogs and screaming kids.

American outposts like Mannheim made sense during the height of the Cold War, but they make little sense today. They are incredibly expensive, inflexible to changes in threat, and packed with support staff who can contribute little to fighting a war.

More than 400,000 American military personnel, along with their dependents, civilian employees and contractors, live in these little Knots Landings abroad. The largest number -- a quarter of a million soldiers, 220,000 dependents and 125,000 civilian employees -- are in Germany; others are stationed in England, Japan, Korea, Italy, the Philippines, Panama and a dozen more countries.

This basing pattern reflects a reality that no longer exists. The number of American troops stationed abroad should and will plummet over the next decade. In Europe, the number will drop from 325,000 to 50,000; in the Pacific from 110,000 to 40,000. Yet some in the Pentagon want to reduce troop levels without changing how they are based. This would be a mistake. Heavily armored troops in a fixed position are the way of the past; Soviet tanks on the Central Plains of Europe no longer pose the greatest threat to our security. Rather we must be ready for the unexpected, with forces that are mobile and quickly deployable.

That's why dual basing is the best system for the future. Here's how it works. Only units that cannot perform their missions if based in the United States -- like those engaged in intelligence collection, host-nation relations, maintenance of pre-positioned war materiel, and treaty verification -- would be permanently based outside the United States. The number of these troops would likely be fewer than 20,000 worldwide.

All other units, including infantry, artillery, fighter aircraft and close air support, would be permanently based in the United States. On a rotation basis, units would be deployed forward for short-term assignments at bare-boned bases. The soldiers' families would remain here near relatives, schools, churches. Short-term deployments could be as brief as a month or as long as one year, as is now the case for unaccompanied tours in Korea. Heavy equipment, including tanks and planes, as well as ammunition, tents, radios, rations and the like would remain overseas.

Bases in foreign countries would be provided by the host nation. If Germany is now willing to pony up $450 million for interim stationing of Soviet troops in East Germany, it should be willing to pay to keep up bare-bones deployment bases for us.

Dual basing occurred to me when I was being briefed on Air Force plans to relocate the F-16s of the 401st Tactical Fighter Wing from Torrejon, Spain, to a brand-new base at Crotone, Italy, at a cost of nearly $1 billion. The planes, pilots and crews of the 401st do not operate out of Torrejon and would not operate out of Crotone. Rather, they deploy to bases in Turkey and Italy to conduct their primary -- if outdated -- mission of striking dropping Warsaw Pact bases. Each squadron, and its associated personnel, is gone from Torrejon about four months a year. The 401st proves that dual basing works; but, why is its home base in Europe? Even ignoring new construction costs, Air Force figures show that it is 16 percent cheaper to operate a wing here than abroad.

Dual basing should be our standard method of operation. The advantages would be enormous. Defense experts, both here and abroad, have long complained that American troops are long on tail and short on tooth. That is, we may have 325,000 troops in Europe, but many of them are civil engineers, cooks, drivers, budgeteers and others who are better suited to managing our extraterritorial American cities than to fighting a war. With dual basing, virtually all American troops abroad will be fighters. This means that 50,000 troops in a dual basing mode can provide as much deterrence in Europe as will 195,000 American troops (the number in the Central Region under NATO's conventional-arms limitation proposal) living in Middle American outposts.

Dual basing would also heighten readiness. Today, U.S. troops based here get ample training and regular exercise in air-to-air combat, tank maneuvers and the like. Troops stationed abroad get limited realistic training to minimize citizen complaints about noise, environmental damage and safety. In Germany, the restrictions are most severe. And, except for a few special units, none of our troops gets much training or exercise in rapid deployment. Dual basing, however, will force deployment exercises by its very nature.

In addition, dual basing is far less expensive than the current system. True, it would entail some added spending for airlift and sealift. But that would be more than offset by savings on base operating costs abroad. According to a Department of Defense report, the cost of our overseas commitment ran $27 billion in fiscal year 1990, excluding any costs for weapons.

In 1988, the United States spent $3.5 billion to construct and maintain bases overseas, $2.7 billion to hire foreign nationals, $1.5 billion for overseas cost-of-living differentials, $1.5 billion to move troops and $2.5 billion to operate overseas bases. Just to operate the overseas Department of Defense Dependents School program (DODDS) for 150,000 kids costs nearly $1 billion a year -- only slightly less than the $1.3 billion we spent on Head Start last year.

Every month, the Pentagon flies 12,000 soldiers and another 10,000 dependents between the U.S. and Germany alone -- enough to fill two 747s every day of the week except Sunday. It costs about $4,000 to relocate an enlisted soldier and family to Germany, and about $13,000 to relocate an officer. And once there, their dollars no longer buy what they used to: In 1987, a greenback was worth 3.5 marks; today, it's 1.6.

To meet the needs of American consumers at these bases, taxpayers spend a quarter of a billion dollars to transport goods to commissaries and post exchanges. Like bringing coals to Newcastle, U.S. taxpayers pay to ship beer to Germany. And we transport 432,000 cases of cat and dog food abroad each year to feed the pets of soldiers. In fact, the Army even ships pet food to Korea, where soldiers are not allowed to take their pets.

The Defense Department ships 750 million pounds of household goods overseas each year at a cost of about half a billion dollars. In 1989, the Army sent nearly 50,000 service member's cars to Europe at a cost of $1,000 per car. Not infrequently, the cost of shipping exceeds the value of the vehicle. Each year, the Pentagon spends about the same amount of money to ship ammunition to overseas bases as it does to transport service members' cars.

Currently, troops are reassigned every two or three years to new bases. This frenzied rotation schedule costs money and often means that no one ever becomes expert in his or her job. Having one-quarter of all U.S. troops stationed abroad is what drives this rotation. With many fewer troops assigned abroad, tour lengths can be extended to four or five years. At the same time, the less expensive forces of the National Guard and reserves can take over more jobs from the active forces. As a result, we will have higher-quality, more experienced staff.

Moreover, while dual basing would cut costs abroad, it would not require any new construction in the United States. We are now closing bases because of excess capacity. It would also eliminate a potential logistical nightmare: Were the Soviets ever to march through Europe or revolution to break out in the Philippines, we would be saddled with a horrendous problem of evacuating dependents. Not under dual basing.

Meanwhile, permanent overseas bases are getting harder to sustain. As the current Philippine negotiations show, some countries regard our bases as violations of sovereignty and extensions of colonialism. Many countries cannot, politically, allow us to maintain permanent bases on their soil. Where we are permitted, it is often because we pay through the nose. According to a 1987 Pentagon study, we are being held up to the tune of $2 billion a year in rental payments for bases, disguised as foreign aid linked to foreign base rights. Now some in the Philippines are talking about raising their rental charge from $500 million to $2 billion a year.

Dual basing is a stable model for burden-sharing. Fair sharing of the common defense burden is more than an equal division of costs. It also means a regime whereby each partner provides what it can best offer. In Germany, for example, dual basing would mean that the Germans provide and maintain training areas, cantonment areas and storage facilities. We would provide the level of troops necessary to provide stability.

Though the world is changing fast, we remain the single benign superpower with global obligations. Threats can come from any direction and call for carefully calibrated responses. Who knows where we might want to deploy troops tomorrow? Dual basing permits us to deal with these threats as they arise. It is not withdrawing from the world, but preparing for new world conditions. It means a stronger military at a lower price.