Why black Africa can't break hidden trade ties with S. Africa

South Africa's flourishing trade with Africa, which the black states pretend does not exist, points up the harsh realities of a continent struggling to cope with world recession, sagging agricultural production, and severe drought.

Next month nine southern African countries will celebrate the third anniversary of a regional effort to break South Africa's stranglehold on their economies.

But South Africa's economic tentacles reach so far into the hinterland of black Africa that its economic grip has in some respects tightened rather than weakened. Certificates of origin may be falsified

''Made in South Africa'' labels may be discreetly removed in the rest of black Africa for obvious political reasons, but from Zimbabwe to Nigeria tins of canned guavas, fresh meat, piles of fresh vegetables, rolls of toilet paper, and an array of household goods make their way to the supermarket shelves from the farms and factories of South Africa. The subterfuge is sometimes achieved through double invoicing and false certificates of origin.

Despite an African ban on trade with South Africa, some 46 African countries turn to the white-ruled state at the tip of the continent for goods or services.

To spare their African customers political embarrassment, South Africa does not provide a breakdown of the individual countries with which it trades.

But figures for the continent as a whole show South Africa's trade with black Africa more than doubled between 1978 and 1980. Official trade figures published by the South African Commission of Customs and Excise establish the value of exports to Africa at $1.2 billion for the first 10 months of 1980.

To some extent Africa finds it has little choice but to trade with a country whose segregationist policies are anathema to it, but whose economic muscle cannot be ignored.

Although occupying only 4 percent of Africa's total land, South Africa accounts for 40 percent of the continent's industrial production. It is the nation with the richest mineral deposits in Africa - ranked first in the world in gold, platinum, chrome ore, manganese ore, vanadium, and fluorite reserves, and second in diamond, uranium, antimony, asbestos, and phosphate reserves. South Africa, according to its embassy in Washington, D. C., produces more steel and electricity than the rest of the continent, and boasts more than half the telephones and vehicles in Africa.

South Africa is one of the very few countries in Africa that can feed its own population. It is also the region's breadbasket, supplying roughly 36 percent of Africa's corn and 18 percent of its wheat. Mozambique, Kenya, Zambia, and Zaire are among the big importers of South African food.

But observers of the African scene say the key to South Africa's economic dominance in the area is its control of transportation - particularly ports and rail lines.

It was Cecil John Rhodes, the gold and diamond magnate with visions of a Cape to Cairo network and the man behind up the Rhodes scholarships, who said that Africa was ''railroads and the rest was fairy tales.'' The validity of that observation is underscored in South Africa's ability to keep the rest of southern Africa in an economically subordinate position through its grip on transportation. Clearinghouse of the subcontinent

Today South Africa acts as the major clearinghouse for the subcontinent, with the most efficient ports and control of 75 percent of the subcontinent's rail network. Freight cars that head as far north as Zaire start or end their journey at South African ports.

More than half of Zambia's major export, copper, is shipped over South Africa's rail network. Zaire's copper shipments are equally dependent because of disruptions to the Benguela line in Angola by antigovernment forces. Roughly 90 percent of Zimbabwe's overseas exports move through South Africa's rail and port system, prompting observers of the southern Africa scene to speculate that if South Africa withdrew its rail services, it could bring about the collapse of the economies of Zaire, Zambia, and Zimbabwe.

South Africa has not been averse to resorting to ''railway diplomacy'' by holding back freight cars. In Zimbabwe this practice caused gasoline shortages and made the point that South Africa can make life difficult for a country that doesn't cooperate or that becomes too critical of Pretoria's race policies.

The problem is compounded for the African states because their own rail lines are either plagued by maintenance problems or have been subjected to sabotage by internal guerrilla movements thought to have the backing of South Africa.

At the same time black Africa is aware that there is no way it can humble South Africa economically. Many bordering states, dependent on the South African economy, would find it counterproductive to do so.

Exporting manpower to South African mines is a key source of foreign exchange for neighboring states. In 1980, Lesotho sent as many as 140,000 workers to South African mines. Mozambique sent 56,000 workers.

The aim of nine African countries - Zambia, Zimbabwe, Angola, Mozambique, Lesotho, Malawi, Botswana, Swaziland, and Tanzania - is not to detach the region economically from South Africa, which is considered unrealistic, but to limit dependence through regional cooperation. This was spelled out at the formal creation of the Southern African Development Coordination Conference (SADCC) in April 1980.

SADCC runs counter to South Africa's hopes of increasing economic cooperation with its neighbor states. The group is seeking some $3.5 billion, mainly from the West, for long-range development programs. About $700 million has been pledged so far.

Central to SADCC's plan is not so much economic integration but the improvement of rail and port connections to avoid reliance on South Africa. Thanks to international donors, funds have been dedicated to building terminals at Nacala, Beira, and Maputo in Mozambique and to upgrading and rehabilitating rail lines to Malawi, Zimbabwe, and Swaziland.

But the tasks facing SADCC are formidable. South Africa accounts for 77 percent of the total production of the 10-state area. Of the SADCC countries, only three - Angola, Mozambique, and Tanzania - are not landlocked. And only two , Malawi and Zimbabwe, produce enough food to feed themselves.

The world recession, sagging commodity prices, and declining agricultural yields have worked against SADCC limiting its dependence on South Africa.

The drought that has exacerbated the situation for the SADCC countries, however, knows no political boundaries. But South Africa has also been badly hit by drought. Its ability to provide food to its neighbors is expected to be sharply reduced.