While the U.S. government has now dropped its ill-designed new towns program, U.S. planners by the plane-load are building new towns in Arabia.

The towns are part of the national economic, urban and social development plans of the mideast countries. Without such planned order, the current, well-oiled building boom - billions of dollars worth of instant harbors, desalination plants, airports, power plants, universities, hospitals, military bases and other projects, most of them designed and managed by Americans - would only result in wasteful chaos.

The most ambitious of the new Arab towns is no doubt Sadat City, to be built from scratch in the Egyptian desert, roughly half way between Cairo and Alexandria. In 20 years, this new city is to have a population of half a million people, to say nothing of innumerable donkeys.

The donkeys are to help avoid the mistakes the planners made in similar new towns in developing countries. They planned almost exclusively for automobile transportation, which proved less than helpful for an economy and lifestyle that relies on donkey carts and small marketplaces.

Sadat City is to have both donkey road, textile mills and steel plants, trails and freeways, as well as rail. It is seen as the best - the essential alternative to the contined urban sprawl of Cairo, which would make that city even less manageable and deprive the country of essential agrarian land.

The economists on the Sadat City planning team - five American and one Egyptian architectural and engineering firms, headed by Parsons Brinckerhoff of New York City - believe the new city may eventually grow to a population of 1.5 million and that two more such new urban centers are needed to keep burgeoning Egypt economically and ecologically healthy.

Ulaya in Saudi Arabia, 8 kilometers from downtown Riyadh, has different ambitions. It is being planned by a St. Louis firm, Sverdrup & Parcel, for only 8,000 people, but hopes to spawn "a generation of 'grass roots' communities" which will serve as "a model for mideast development."

Ulaya, which will include its own schools, mosque, health services and recreation, is to be a satellite to rapidly expanding Riyadh, absorbing its population "overspill," as the British call it.

Here, too, the key to success is a judicious combination of introducing new technologies and maintaining ancient traditions. Not all of these are as quaintly romantic as donkey carts. Some are oppressively reactionary such as the strict prohibition against women driving automobiles.

Also in Saudi Arabia, the St. Louis architects Hellmuth, Obata and Kassabaum, who gave Washington its handsome Air and Space Museum on the Mall, are giving Riyadh an instant, $3 billion university for 21,000 students. On order of Sheikh Hassan Abdullah Al-Sheikh, who is in charge of education, the university must be open on June 18, 1982, complete with mosque, library, auditoria, computer center, food services, power plant, sports stadium and all the rest.

This is quite a feat, considering that every hail and all other building tools and materials must be imported, even sand. (Saudi desert sand is not suitable for concrete.) Everything must be imported without any rail or even adequate truck roads. Nor is there any local labor. Those of the five to 10 million male Saudis who do not serve in the military prefer a nomadic life, raising camels. All contruction workers are brought in from South Korea, the Philippines, Turkey and a few other places.

Hellmuth, Obata and Kassabaum teamed up with one English and three other American firms to bed for this mind-boggling job in an international competition called directly by the Saudi authorities. The team presented its design proposal in two volumes, bound in $4,000 worth of green Morocco leather, emblazoned in gold and fitted into specially designed leather suitcases.

Most American design and construction work in Saudi Arabia, however, is contracted for and managed by the U.S. Army Corps of Engineers Middle East Division in Berryville, near Winchester, Va. The arrangement was made in 1965 in an official treaty which keeps being extended and which returns some of the money we pay the Saudis for their oil.

The treaty has also made Berryville the new Mecca for American architects, contractors and engineers. The Corps of Engineers, however, claims to be unimpressed by Morocco leather.

It has the reputation, instead, of achieving something in Saudi Arabia which we have never been able to achieve on large construction jobs and comprehensive development programs in the United States - management efficiency.

This proves, as our moon landing has already proven, that impossible conditions, such as 100 degree temperatures, unhappy Koreans and the absence of paper clips or even gravity, are easier to cope with than American municipal politics, building trade unions and federal regulations.

But the conditions which have led the Arab nations and virtually every country on earth to plan urban development on a national or at least regional scale and to contain it in comprehensively planned communities, also prevail in the United States.

Like Egypt and other countries, the United States has come to the point where we must preserve agricultural land and open spaces. Both Egypt and the United States must check urban sprawl and concentrate future urban development and industrialization in planned settlements or new towns.

Like most developing countries, the United States must bring workers and jobs together to avoid overtaxing commuter traffic and open up job opportunities for the underprivileged. In the developing countries the underprivileged are in the rural areas. In the United States they are cooped up in inner city ghettos. The problem is pretty much the same. And so is the solution: comprehensively planned communities, or new towns, where new workers and new industries come together under favorably designed new conditions.

I could go on, for the arguments in favor of national and regional planning and for new towns are many. But other countries have accpeted them and this country has hopelessly discredited them.

With the exception of Reston and Columbia, two successful new towns which were never part of the defunct federal program but which can never be repeated as private enterprises, the very idea of planned communities makes politicians run for cover and planners shrug their shoulders in frustration.

Luckily, we are a forgetful nation. In a few years we will look with pride at the new cities American knowhow has built in Egypt, Saudi Arabia and elsewhere. Some public relations expert will give the new town concept a new name (just as rowhouses were renamed townhouses) and all will be forgiven.

By some other name and some other management, we too, will plan our regions and our communities - and catch up with the Arabs and the rest of the world.