Johannesburg — As South Africa prepares to ''go nuclear,'' hopes and fears about the implications of the move are rising. The start-up of South Africa's first nuclear power station, expected within the next few months, is a worrisome development for those concerned about the spread of nuclear weapons around the world.
But United States officials are expressing optimism that South Africa will soon issue at least partial assurances that it has only peaceful intentions in the nuclear field. These US sources say talks with South Africa on nuclear issues have made ''substantial progress.''
South Africa's movement into nuclear power production is by itself a peaceful step. But in going nuclear South Africa will demonstrate - as it has in a number of other fields - an impressive yet worrisome ability to defy outside pressure.
In this case the pressure has been aimed at ensuring that South Africa does not develop nuclear weapons. So far, however, the development of such weapons remains a very real possibility.
The United States has been the key actor in trying to get South Africa to sign the Treaty on the Non-Proliferation of Nuclear Weapons and to accept outside inspection of its nuclear facilities to ensure there is no weapons development.
So far, South Africa has refused to do either.
The facility that most concerns those worried about South Africa's nuclear capacity is the Valindaba uranium enrichment plant concealed in the hills near Pretoria, the nation's administrative capital. Although South Africa has agreed to put its new Koeberg nuclear power station near Cape Town under international inspections, it has refused outside access to Valindaba. South Africa claims it shields Valindaba from outside eyes for proprietary purposes. A knowledgeable source says Valindaba is highly efficient and economical.
Another sticking point on the inspections issue is South Africa's relationship with the United Nations International Atomic Energy Agency. The IAEA is the body that carries out inspections. It is considering expelling South Africa from its membership.
South Africa remains a member at this point, but it was voted off the IAEA board of governors in 1977. And at a meeting last September, the IAEA decided to investigate South Africa's future role in the body.
Close observers have always suspected that political motives also play a role in South Africa's stance regarding inspections and the Non-Proliferation Treaty. These analysts are convinced that South Africa was preparing for a nuclear test at a site in the Kalahari Desert in 1977.
Although Western pressure forced South Africa to discontinue whatever it was doing in the desert, many analysts say it has continued to benefit from the uncertainty about its nuclear program.
While South Africa denies any intention to make nuclear weapons, some analysts feel it has the know-how to initiate a weapons program if pressed. By not agreeing to inspections and not signing the Non-Proliferation Treaty, South Africa keeps black Africa and other potential enemies guessing, some analysts say.
The development of Koeberg was initially seen as an opportunity for outside pressure on South Africa. Pretoria conceded it would need enriched uranium from the outside initially to fuel the nuclear plant. By 1987 Valindaba is expected to be able to provide all the fuel Koeberg will need. South Africa signed a contract with the US Energy Resources Development Agency in 1974 to have uranium enriched in the US and then returned to South Africa.
But the US has refused to supply the enriched uranium since President Gerald R. Ford suspended such exports in 1975. US restrictions were strengthened with the passage in 1978 of the US Nuclear Non-Proliferation Act, which calls for states to accept full inspection of their facilities before they can receive uranium enriched in the US.
It also is US policy that South Africa sign the earlier Non-Proliferation Treaty before receiving enriched uranium.
But whatever leverage the development of Koeberg offered the US quietly slipped away in 1981, when South Africa was able to obtain enriched uranium without US cooperation.
Reportedly, the uranium supplies came from private sources in Switzerland and Belgium. So from the South African side, there has been no urgency to come to an agreement with the US.
South Africa points out that it is not alone in not accepting inspection of its enrichment facilities. The US itself has not accepted inspection. But of course, the US is already openly a nuclear weapons producer.
One thing Washington has faced in negotiations with Pretoria is South Africa's considerable iBditation over the US's restrictive actions in the nuclear field after years of close cooperation. South Africa provided the US with uranium in the 1950s for America's nuclear weapons program.
Also, the United States provided South Africa with the fuel and hardware for its Safari-1 research reactor, which began operation in 1965.
Koeberg consists of two units. And when both are producing at full capacity (they are expected to do so by early 1985), the faciiity will produce close to 2 ,000 megawatts of power. That will supply about 6 percent of South Africa's total electricity requirement.
Koeberg was originally expected to be functioning in 1982. But there was a sabotage attack against the plant late that year. African National Congress rebels claimed responsibility for the series of four explosions that ripped through the facility.
But South Africa is undeterred. Its nuclear industry is expanding.
The Atomic Energy Corporation has announced that its activities have outgrown the present site, which holds both Valindaba uranium enrichment plant and the adjacent Safari-1 research reactor at Pelindaba. A separate ''nuclear research center'' will be built along South Africa's south coast, just west of Mossel Bay.
South Africa has no official plans to expand its nuclear power industry beyond the construction of Koeberg. But close observers believe an expansion is highly likely.
There are strong economic reasons for nuclear power. South Africa has an abundance of coal, now used for generating the country's electricity. But it would like to conserve coal for the production of synthetic liquid fuels and for exports that would earn foreign exchange.
Although there are no plans to expand Valindaba so as to meet the enriched uranium requirements of an expanding nuclear power industry, a spokesman for the Valindaba plant says it would be ''fairly simple'' to the site's activities, should the need arise.