Johannesburg — The ''costs'' and ''benefits'' of President Ronald Reagan's reported tilt toward South Africa should come into sharper focus this month.
United States Vice-President George Bush this week begins a 13-day trip to seven African states - Cape Verde, Senegal, Nigeria, Zambia, Zimbabwe, Kenya, and Zaire - to, in his words, ''learn what key African leaders are thinking.''
The trip makes Mr. Bush the highest-ranking member of the Reagan administration to visit black Africa.
The Vice-President will no doubt get a feel for the costs of Reagan administration policy in Africa, a policy that stresses a friendlier attitude toward South Africa and that thereby strains relations with black Africa.
Another spotlight on US-Africa relations will light up later this month when South African Minister of Foreign Affairs Roelof Botha is scheduled to call on US Secretary of State George Shultz. The meeting will be mainly a ''get acquainted'' visit, according to diplomatic sources. But the two leaders are expected to discuss the troubled negotiations on Namibia (South-West Africa). Settlement on Namibia, a territory South Africa has illegally occupied since the mid-1940s, has been held out as one of the main benefits of closer US-South African ties.
The State Department calls reports that Namibia talks are stalemated ''grossly inaccurate,'' but diplomatic sources concede there is a growing ''nervousness'' on the part of the United States. The concern is over rising impatience within black Africa - particularly among the ''front-line'' states of Angola, Zambia, Botswana, Zimbabwe, Tanzania, and Mozambique - that Reagan's tilt toward South Africa has failed to achieve its goals, at least on a Namibia settlement.
Some senior State Department officials are expected to visit South Africa in the next few weeks and may lay groundwork for talks between Shultz and Botha.
Holding of such a meeting also may suggest there is no present plan to shift policy on South Africa. But critics are likely to raise questions about what the meeting achieves.
President Reagan's policy of ''constructive engagement'' toward South Africa is built on the premise that the United States can better encourage change through friendly encouragement than harsh criticism. Officially, the US remains opposed to apartheid, but it is not aggressively critical of South Africa's racial policies.
President Reagan ''normalized'' relations with South Africa after severe strains during Jimmy Carter's administration. For example, the number of defense attaches at embassies in Washington and Pretoria have been returned to full strength. And President Reagan has liberalized trade policy with South Africa.
The United States also has been a high-profile defender of South Africa on some occasions. Last year the United States vetoed a United Nations Security Council resolution condemning South Africa's invasion of Angola - an act that marked an important split between the US and its West European allies.
Earlier this month the US spoke out in defense of South Africa receiving credit worth $1 billion from the International Monetary Fund. The US supported the IMF loan on the basis that politics should not enter into such decisions. Still, during a UN debate on the loan, a US representative reportedly spoke of ''constructive change'' taking place in South Africa.
Indeed, the Reagan administration has looked favorably on limited proposals for ''power-sharing'' that have been introduced by South African Prime Minister P.W. Botha. The US considers them a step in the right direction.
These reforms would give Coloreds (persons of mixed race descent) and Indians representation in the central government. But they would continue to leave out blacks, although blacks make up some 70 percent of the South African population. Many critics dismiss this step as mere window dressing; others say it would cause white-black relations to deteriorate further.