Johannesburg — In the posh ''white'' suburbs north of this city it can take many months to get new phone service and up to three years to obtain a post office box.
South of Johannesburg in the sprawling ''black'' township of Soweto, thousands have given up waiting for government-provided housing. They have moved their families into garages or backyard shacks, paying top dollar for the privilege. Similar accommodations are taken by large numbers of ''illegal'' residents who do not have government approval to live in Soweto.
At both ends of the city a similar force is at work: a major shift in population away from the countryside to the cities, and away from the southwest to the industrial heartland of the northeast.
The population movement is spelled out in provisional 1980 South African census data. Behind the numbers and statistics are some rather unpleasant realities for the South African government.
Like many other nations, South Africa must decide how to cope with rapid urbanization. Major metropolitan areas, particularly the Johannesburg-Pretoria-Vereeniging complex in the northeast, are finding the cost of city services is running away from the available supporting tax base.
The South African government looks on the rapid urbanization with concern not only for economic development problems, but also for its political implications.
South Africa's minority white government has officially labeled the major metropolitan areas ''white.'' Blacks are subject to a web of influx and pass-law controls that limit their rights and movement in the urban areas.
Blacks have been granted their own tribal states in the rural areas. There was a time when the government felt blacks eventually would choose to migrate back to these ''homelands,'' leaving city life behind.
The census makes clear that is not happening. Rather, urbanization of blacks has increased and is likely to accelerate, according to Dr. P. Smit of the Human Sciences Research Council. Dr. Smit estimates that 60 percent of the South African population is now urbanized. That is high compared to most developing countries, but low compared to most industrialized, Western nations.
The important point for South Africa is that urbanization is making the white cities increasingly black. Whites, representing only some 17 percent of the South African population (including the homelands), are nearly 90 percent urbanized. And whites are now approaching a zero population growth rate.
The majority black population is growing at a rapid 2.5 percent annual rate and is only 38 percent urbanized.
According to the Human Sciences Research Council, that means the urban black population may increase by about 1 million per year for the next two decades. By the year 2000 South African cities will have at least 20 million blacks and perhaps 4.8 million whites.
That raises the thorny question of how the government will deal with the growing political aspirations of urban blacks. They have no vote now, and the blueprint for separate development has envisaged them having a political voice only in their ''homelands.''
The government has indicated it no longer considers black townships like Soweto ''temporary,'' and it speaks of the need for some ''accommodation'' for urban blacks. But the ruling National Party still seems divided over whether blacks should be granted some local or metropolitan political rights, or whether the government should pursue the idea of linking urban rights with the homelands.
For the most part, urban blacks reject the legitimacy of the homelands as an outlet for political representation.
The economic consequences of urbanization, particularly as it focuses on the northeast region, are considerable. It is not in South Africa's interest to overexploit the resources of one region, while development potential is ignored in other areas.
The lure to the northeast is jobs, relatively good wages, and the amenities that come with a well-developed urban environment.
The options for the government are limited. A more heavy-handed system of influx control to keep blacks out of the cities could create its own unrest and frustration among blacks. The opposite extreme -- allowing unhindered access to the cities - appears out of the question for the government.
The government has a plan, using tax concessions and cash incentives, to spur regional development and industrial decentralization. But that will not in itself stall the expansion of the urban population, most analyses agree.
With more blacks in the cities, the South African government will face rapidly rising costs if it sticks to its commitment to equal, but separate, services such as education. Already some 30,000 new homes are needed.
Given the housing shortage, the demand, and economic constraints, Dr. Smit says ''new thinking'' is needed about building standards for blacks. He maintains that existing housing is over-built and that more homes can be built faster with less stringent standards.
South Africa's Building Industries Federation disagrees. It urges that blacks be allowed to have freehold title to land as a means of encouraging more private capital investment in black townships. Currently, blacks can have only a 99-year lease on land.