Soviets bolster an Arab ally. Military buildup in South Yemen worries US officials

The Soviet Union is engaged in a major buildup of military equipment near the strategic tip of the Arabian Peninsula, according to United States government officials. New Soviet tanks, air defense weapons, and fighter jets are being stockpiled there at bases in the desolate nation of South Yemen, US sources say. The amount of weaponry appears to be far in excess of what South Yemen's own military forces require.

The purpose of the buildup isn't clear. But the increased Soviet presence in the region makes US analysts nervous, as sea lanes crucial to delivery of oil from the Gulf lie off the South Yemeni coast.

``We're worried,'' says a knowledgeable State Department official.

At one location, the Soviets may have stored enough equipment to outfit a brigade of troops, US sources say. South Yemen's Air Force may have been upgraded with MIG-23 aircraft.

A mysterious nation long troubled by fighting among tribal factions, South Yemen is the Soviet Union's closest Arab ally.

Soviet ships have access to the port at the capital of Aden, once a key refueling stop for Britain's Royal Navy. Socotra Island, near the Arabian Sea, has a Soviet airfield and naval facilities. There are at least 1,000 Soviet military personnel and advisers in the country, according to the Pentagon.

The current Soviet military buildup has its roots in a January 1986 coup during which Aden erupted in a civil war that was both brief and remarkably ferocious.

The US Defense Department charges that Moscow abetted the faction rebelling against President Ali Nasir Muhammad to solidify its grip on the country. Academic analysts, however, generally conclude that the Soviets were surprised by the uprising, and that both Yemeni factions struggled to win Moscow's support during the fighting.

In any case, President Muhammad was quickly ousted. Since then the Soviet Union has moved to increase its influence in and impose stability on a quixotic country that is key to the Soviet position in the Middle East and the Horn of Africa.

During the civil war, up to 145 South Yemeni tanks and perhaps 90 percent of the country's Air Force equipment was destroyed or seriously damaged, according to the International Institute for Strategic Studies in London. Thus, for two years Soviet arms have been pouring into South Yemen to rebuild its forces.

It's possible that the stockpiles of new Soviet weapons are only for the locals. ``Whether or not the South Yemenis themselves can use all this stuff is hard to tell,'' says a State Department official.

Deposed President Muhammad has taken refuge with a smattering of loyal forces in neighboring North Yemen. The new South Yemeni regime may consider him a military threat that requires the response of a military buildup.

The USSR may also be worried about an invasion of their Yemeni ally launched by outside countries, Arab or Western, that feel they can take advantage of a new regime, argues Fred Halliday, a London School of Economics Mideast analyst

But US officials say the influx of weapons has reached the point where the Soviets could be stockpiling for themselves. (For its part, the US has positioned some military equipment, notably munitions and food, in neighboring Oman.)

The quantity of Soviet weapons has surpassed previous levels used by South Yemen. It contains communications gear, air defense weaponry, and other sophisticated equipment the Yemenis may not need. Portions of it may be stored as if prepositioned for an expeditionary force.

Officials declined to reveal the location of Soviet stores, saying it could reveal intelligence methods.

Whoever their intended user, the new weapons, analysts say, threaten Western interests and influence in two areas:

In the Arabian Peninsula, the South Yemenis have a history of belligerence against neighbors. They have outstanding border disputes with Oman and Saudi Arabia - both US friends - and could conceivably decide to seize territory by force. They are also on less than good terms with North Yemen, which is moderately friendly toward the West.

At the Horn of Africa, crucial sea lanes to the Suez Canal lie just off the South Yemeni coast. In a conflict, weapons stockpiled in Yemen might help the Soviets close the entrance to the Red Sea - shutting the Suez Canal's back door.

Somalia, just across the Gulf of Aden from South Yemen, provides the US military with access to bases. But Congress continues to cut US aid to Somalia, officials complain.

``There is a sense that the great US interest of the early '80s [in the Horn of Africa] has dissipated,'' a congressional staff member says.