Reagan reaches threshold. Moment of decision arriving for Washington on arms control and South Africa sanctions

Events in world affairs this week brought Ronald Reagan to the threshold of two of the most important foreign policy decisions of his presidency. One is whether to do serious arms control business with the Soviets. The other is whether to align the United States openly with the rising tide of black aspirations in South Africa.

The stakes are enormous.

A decision to reach for a major agreement with the Soivets would please the Western allies and strengthen the bonds of NATO. A failure to take advantage of the opportunities of the moment would loosen the bonds of NATO and could even drive the Western European allies into a neutralist position between the US and the Soviet Union.

A decision to give open support to black aspirations in South Afirca would neutralize Moscow's present role as friend and sponsor of black nationalism in southern Africa. A decision against open support for black aspirations would alienate the black community in South Africa and put Moscow on the inside track when the rising black tide spreads over the last bastion of white rule in Africa.

The need to decide on serious business with the Soviets, for or against, was precipitated by the latest set of Soviet proposals on arms control filed in Geneva the week before and outlined orally this past week by Mikhail Gorbachev. The new proposals were novel and imperative in that they omitted the standard impossible features of previous Soviet proposals.

So long as the Soviet position required abandonment of President Reagan's Strategic Defense Initiative (popularly known as ``star wars''), there was no need to go to any conference. The proposals were not serious. But this time Mr. Gorbachev offered to permit ``laboratory'' work on SDI. This means that he is ready to bargain.

Also, Gorbachev has dropped a demand that British and French strategic weapons be counted along with US weapons in the balance. Neither Washington nor London nor Paris would agree to that. Hence it was an impossible condition, meaning that Moscow was not serious.

There are no impossible preconditions in the latest set of Soviet proposals.

Heretofore Moscow has put forward arms control proposals for propaganda advantage. They always contained impossible preconditions. The difference this time has been recognized in Washington. Normally any Soviet proposal is answered instantly and reflexively by a counter-propaganda barrage pointing out the impossible features of the Soviet position. During the last week, Washington fired no counter-propaganda barrage.

The silence in Washington attested to the fact that Washington had recognized the new elements in the Soviet position.

Washington also sent a private letter from Mr. Reagan to Mr. Gorbachev, and Washington proposed to advance the next meeting between the foreign ministers. Washington has not, as of this writing, said publicly, ``we are ready to talk.'' But it has said, in the language of diplomacy, ``We recognize that you are ready to talk and we would like to talk about that.''

In other words, the first door hitherto blocking the way to serious business between Moscow and Washington has been opened.

There are more doors down the long corridor ahead. Meanwhile, the time had apparently arrived when he could not much longer defer a decision about South Africa. Up to now he has stood on ``constructive engagement,'' which is a diplomatic masterpiece of ambiguity. It is supposed to mean to South African blacks that the US is trying to help them in private, but to South African whites that the US is not pushing seriously.

Such an ambiguous posture is all very well, so long as there is a prospect of a long-term, gradual progression in South Africa from all-white to mixed rule. This is what Washington, and the West European capitals, have hoped could happen in South Africa.

But the pace of change has quickened. Most experts on South Africa have reached the point of assuming that it is now too late for a gradual and peaceful transition.

After gaining independence in Ghana and Nigeria, black Africans won a big success in Kenya in 1963. Since then, every African country that had been white-ruled before World War II had passed from white to native rule, except for South Africa. It is the last stand of European whites in Africa.

The US backed the winning blacks in Kenya, and later in Rhodesia (now Zimbabwe). The Soviets backed the winning blacks in Angola and Mozambique. Kenya and Zimbabwe are in the Western economic orbit today. Angola and Mozambique are in the Soviet military orbit, although they do most of their trade with the West.

Washington will stall to the last possible moment, and hope that it will not end up backing the ultimate losers, as it did in China and Vietnam. But pressure is mounting in the US Congress. Legislation calling for economic sanctions was introduced this week.

But on Monday last week, business and industry closed down in South Africa, as blacks remembered the bloodshed at Soweto 10 years ago. The country cannot function without black labor. And black labor is demanding with increasing intensity a share in government.

The serious question is whether the Soviet Union or the US becomes the closer friend of the ultimate future rulers of South Africa. Reagan must decide, and soon.