S. Africa, Zimbabwe 'swap' blacks and whites

* A white engineer from Salisbury says he would ''stick it out'' in black-ruled Zimbabwe, but he sees no future for his children in a socialist country. Reluctantly, he says, he has decided to move to South Africa.

* A black gardener in Johannesburg has been given until mid-1982 to leave South Africa and return to Zimbabwe. He, like some 20,000 other Zimbabwe citizens working south of the Limpopo River, has been told by South Africa to return ''home.''

The cases of these two men, reluctant to move but moving anyway, are typical of the individuals involved in a large population ''swap'' between Zimbabwe and South Africa. They illustrate one of the most tangible results of the diverging ideologies of the two nations.

The movement of people between the two countries is at its peak right now. But the consequences for both countries are apt to be long-term and subtle.

For South Africa the trend has political implications. Disgruntled white Zimbabweans come to this country bearing the message that black majority rule is a disaster. They tend to be a vocal constituency against fundamental change in South Africa's political system of white minority rule.

For Zimbabwe the results of the exodus of whites and repatriation of black laborers appear to be mainly economic. Departing whites take with them important skills needed in Zimbabwe. And the arriving blacks, most of them unskilled, only worsen the high unemployment.

Recent figures indicate that a record number of whites left Zimbabwe last year. As Prime Minister Robert Mugabe's government settles in, a growing number of whites seem uncertain about their future in Africa's newest nation with black majority rule.

Like the white engineer from Salisbury, many departing whites are increasingly put off by Mr. Mugabe's socialist ideology and the decline they are sure it is bringing in the standard of living for whites.

According to government statistics, well over half of the 20,500 Zimbabweans who left that country in 1981, took up residence in South Africa.

Moving in the opposite direction are some 20,000 blacks caught directly in the continuous war of words between Salisbury and Pretoria.

Last week the final busload of Zimbabwean mine workers left South Africa for the trip north. Over the next year the remaining 16,000 Zimbabwean gardeners, domestics, and other unskilled laborers will depart as their labor contracts in South Africa expire.

Pretoria began sending Zimbabwean workers home last year when Mr. Mugabe's government said it would no longer permit South Africa's mining industry to recruit labor in Zimbabwe. The move was accompanied by charges from some government officials that South Africa was exploiting Zimbabwean workers and using some as ''slave labor.''

The result has been that the two countries have stopped cooperating in any respect on labor matters. South Africa will no longer renew the work contract of any Zimbabwean.

The South African government will make exceptions only if a worker has worked continuously for one employer since 1958 or for a variety of employers since 1953.

The Black Sash, a South African women's organization, points out in its 1981 annual report the hardship the new policy poses for Zimbabweans who have spent all of their working lives in South Africa. Many have married South African women and have raised children here.

The major fear of many Zimbabweans is that they will not find work or be able to support their families if they return home. Unemployment among the unskilled in Zimbabwe is high.

For black mine workers and their families, the loss of income from South Africa is significant. The Employment Bureau of Africa, which recruits labor for the South African mines, says almost $6 million was repatriated to Zimbabwe in 1981 by mine workers in South Africa.

Black Sash sees a certain double standard in operation as the South African government sends black laborers back to Zimbabwe while it accepts whites from that country in high numbers. But an immigration official for the South African government insisted white Zimbabweans received no favored treatment in coming to South Africa.

The main requirement is that immigrants have the job skills needed in South Africa--a criterion that basically excludes unskilled black laborers from gaining the right to live here.