Johannesburg — South Africa has made two gestures toward improving relations with neighboring black Africa.
* Prime Minister P. W. Botha has responded favorably to Zambian President Kenneth Kaunda's proposal that the two leaders meet publicly.
If the meeting takes place, it would represent the first public encounter between South African and a black African head of state since 1975.
* South Africa extended its preferential trade agreement with Zimbabwe. This sign of economic goodwill reverses South Africa's decision last year to terminate the agreement on March 24.
The economic benefits of the trade pact accrue mostly to Zimbabwe, so foreign affairs analysts here see the motivation for its extension as mainly political. The move sharply contrasts with some past Pretoria actions - such as withdrawal of rail locomotives in early 1981 - which were economically disruptive to Zimbabwe.
The two South African actions could have wider implications.
Formal talks between presidents Kaunda and Botha could lead to greater respectability for South Africa among its neighbors. Pretoria's racial policies and occupation of Namibia (South-West Africa) have increasingly estranged it from black states.
For the region as a whole, Zambia-South Africa talks could provide a ''change in direction after a number of years in which tension has steadily increased,'' says John Barratt, director of the South African Institute of International Affairs.
President Kaunda's offer to meet publically with Mr. Botha was surprising in that it came in an interview with a reporter, rather than through diplomatic channels.
The Zambian President cited Namibia (South-West Africa) and escalating violence in South Africa as the topics he wanted to discuss with the South African government.
The trade agreement with Zimbabwe may also wipe some tarnish off South Africa's image. If Zimbabwe was not granted an extension of favorable tariffs for its goods, the nation might have lost $40 million worth of of exports and 6, 000 jobs, according to economists in that country.
However, it should be noted that trade pact is also in South Africa's interest; it maintains Zimbabwe's heavy economic dependence on South Africa, a dependence Zimbabwe wants to reduce.