The Zambian-born white farmer got on the regular afternoon flight from northern Ndola to Lusaka and was startled to see that the entire crew of the aircraft was white. When the hostess later announced flight details he recognized the accent as distinctly from Zimbabwe-Rhodesia.

"The whole bloody crew was Rhodesian and they were flying on a Zambian Airways internal flight," he remarked in amazement, recounting his adventure a few months after the first Rhodesian air attacks on Zimbabwean nationalist guerrilla camps deep inside Zambia.

The explanation for the Rhodesian crew was at once very simple and complicated. But it illustrates how closely the economies of the white- and black-ruled nations of southern Africa are linked in total disregard for the raging political battle taking place among them.

Zambian Airways, apparently short an aircraft, had subleased the plane from the tiny airlines of neighboring Botswana. It, in turn, was leasing the aircraft from a charter firm based in nearby Swaziland that normally resorted to either South Africa or Rhodesia for its crew and maintenance.

This, it seems, explains why travelers repeatedly see the same unmarked green and white Viscount alternately in Salisbury, in the Botswanan capital of Gaborone, and in Lusaka. In fact, at one point it was being used to shuttle nationalist guerrilla recruits and Rhodesian refugees from Botswana to Zambia.

A newcomer to southern Africa is at first surprised, or even shocked, to learn of such strange goings-on between the black African states north of the Zambezi River and the white-ruled or white-supported states to the south. After all, in theory and rhetoric, they are sworn enemies and the black states are dedicated to ending all vestiges of white minority rule in southern Africa.

But one quickly discovers that despite all the African talk of an economic boycott against South Africa and outrage over Western violations of the sanctions imposed on Zimbabwe-Rhodesia, such examples of black-white "cooperation" are commonplace and becoming more so every day.

Indeed, the truth of the matter is that the hard economic realities of the region today are increasingly forcing the black states as far north as Zaire to depend on South Africa, and often even Zimbabwe-Rhodesia, for their survival.

Fully aware of this, South Africa is seizing the occasion to promote a constellation of southern African states grouped under its umbrella in some kind of regional economic and political bloc. tthe idea is getting the official cold shoulder in all balck capitals but still not stopping them from stretching out a hand for economic help to Pretoria with ever greater frequency.

Whether South Africa will ever succeed in parlaying its growing economic influence throughout southern and central Africa into political capital remains to be seen. But the black and white leaders of Zimbabwe-Rhodesia are seeking to use their stranglehold on Zambia's southern road and rail routes to squeeze President Kenneth Kaunda into reducing his # support for Joshua Knomo's guerrillas fighting to overthrow them.

So far, Kaunda seems to be holding fast and simply pressing the guerrillas to get into Zimbabwe-Rhodesia as fast as they can before he is forced into a compromise.

Ironically, the most successful use of South Africa's economic power to date has been against white-ruled Rhodesia. In the late summer of 1976, Pretoria halted all war supplies and other vital imports into Rhodesia for a few days to force former prime minister Ian Smith into accepting the British-American demand for black majority rule.

The two great symbols of the southern African economic nexus are the railway systems and the electrical power grids. Their tentacles tie together the economies of Mozambique, Zambia, Zaire, Botswana, Swaziland and Lesotho to those of Rhodesia and South Africa in ways that are sometimes unimagined and seldom mentioned publicly.

For example, Zaire ships about half of its copper exports, and Zambia 43 percent, southward along the railway snaking from Lubumbashi in Zaire to Lusaka and across the bridge at Victoria Falls and on through Rhodesia into South Africa.

Most of this railway is part of the Cape-to-Cairo scene promoted by the British empire builder and colonial entrepreneur, Cecil Rhodes, late in the 19th century. The Chinese-built Tazara Railroad that was meant to reroute Zambian and Zairian traffic eastward to the Indian Ocean has not proven a successful substitute for this old historic north-south route leading deep into the heart of Africa.

Zaire not only exports half its copper out on this line but brings in hundreds of thousands of tons of coal and food supplies that keep alive the southern third of that country. Zambia, too, uses the same railroad to import a wide range of South African products to keep the wheels of its depressed economy turning, from machinery for the copper mines to soap detergents, oil and baby food.

Less well known is the fact that Zambia and Rhodesia, political arch enemies, are totally integrated on the same electrical power grid from the northern Zambian copperbelt towns of Ndola and Kitwe to the Zimbabwe-Rhodesian capital of Salisbury.

The two share equally the 1266 megawatts generated from the power stations located on the north and south sides of the Kariba Dam and administer its use jointly within the Central African Power corporation headquartered in Salisbury.

The integration of grids means, among other things, that the sub-power station on the outskirts of Lusaka can be controlled from Salisbury and that Zambia can, and does, sell its excess power to Rhodesia. For example, during the 1977-78 fiscal year, Zambia earned $14 million from the sale of electricity to Rhodesia, according to the corporation's spokesman in Salisbury.

"It would not be practical for either of us to cut off the other," remarked a ministry of power official in Salisbury explaining the complexities of the power sharing.

In the past few months, a number of signs of the expanding economic role of South Africa and Rhodesia in neighboring black African states have come to public notice. These include:

In late February, South Africa signed a seven-year agreement with Marxist Mozambique to double its exports through the port of Maputo to 12 million tons. South African mines are to finance the upgrading of harbor facilities of the rail line between Maputo and Komatipoort.

South Africa reportedly has also agreed to extend a $140 million line of credit to mozambique so it can buy general goods including about 100,000 tons of corn this year.

South Africa has loaned Zambia six locomotives, is training Zambian drivers and has dispatched more than 2,000 railway cars up here to deliver general goods and take out copper. More than 2,000 cars were recently "stuck" here and South Africa refused for two weeks to send anymore until some were returned. CAPTION: Map, no caption, The Washington Post