Waging a war of sabotage in South Africa. The African National Congress dazed South Africa's white rulers when it hit high-security police and power installations in 1982 and '83. The outlawed movement, which went underground in 1960, claims it is forced to resort to sabotage because all nonviolent channels of protest have been closed by the government

The atmosphere was electric. Thousands of blacks were marching on Johannesburg. Tens of thousands were marching on Cape Town. The police and Army roared into action. Roadblocks shot up. Tanks rolled into position. Jet fighters buzzed African crowds at rooftop level.

The time: March 1960. It was the month of mass passive resistance demonstrations against the South African race laws. It was also the time of Sharpeville, when 69 Africans protesting the carrying of passes were shot dead by the South African police.

The South African government was facing its sternest test. There was an alarming flight of capital out of the country. Either the government would regain control through a massive crackdown, or the resistance movement would seize this opportunity to change the existing apartheid order.

Reports of nationwide unrest snowballed on the day of Sharpeville. A prominent professor on the small campus of the University of Natal in Pietermaritzburg then gathered his white students together, and in the hushed tones of one who believes history is in the making, said flatly: ''I think the government will fall tonight.''

''We thought exactly the same thing at the time,'' says Mfanafuthi Makatini, who heads the observer mission to the United Nations of the outlawed African National Congress (ANC).

The government didn't fall. It prevailed through batons and banning orders, through sweeping pre-dawn raids on the houses of suspected revolutionaries and through a flurry of legislation that tightened the screws on political dissent. African (black), Indian, and white opponents of the government were scooped up in the detention net.

Organizations such as the ANC and its rival, the Pan African Congress (PAC), were banned shortly after Sharpeville. Hundreds of activists like Mr. Makatini and the ANC's current president, Oliver Tambo, escaped through neighboring African countries and regrouped to fight another day.

The dawning of that day has apparently come. For within the last two years the underground resistance movement, which has become virtually synonymous with the ANC, has carried out over a hundred highly selected acts of sabotage that have put South Africa's security forces on edge and left whites uneasy about what might follow next.

Ruth Mompati, chief executive of the ANC's branch in the United Kingdom, says that what agitates the South African authorities is that the ANC has been able to carry out daring acts of sabotage under the noses of South African security forces. In a recent interview in London, she said:

''We hit Sasol (the oil-from-coal refinery near Johannesburg), which is high security. And then we hit Koeberg (a nuclear power station near Cape Town), which is also high security, twice in a month. First they said it was an electrical fault that would take six weeks to correct. We didn't worry. We went back again. We hit it four times at regular intervals with limpet mines. They couldn't say it was an electrical fault after that. They couldn't believe it could happen in the heart of their Afrikanerdom. This is what is making South Africa so angry, and their followers are starting to see their weaknesses.''

By all accounts, including reports from South African intelligence, Pretoria has seen the enemy and the enemy is the ANC.

How vulnerable, then, is the South African government? Who belongs to the ANC , and what is its strategy? To what extent will strife in South Africa drag in South Africa's closest black neighbors - Angola, Zambia, Botswana, Lesotho, Zimbabwe, Swaziland, Mozambique, and Tanzania - to which South African political opponents have fled?

These questions are uppermost in the minds of Africa watchers. They have become more pressing since the ANC claimed responsibility for the May 20, 1983, bomb attack outside Air Force Headquarters, Pretoria. As many as 17 people were killed, eight of them black, and more than 200 injured in South Africa's worst incident of sabotage.

The blast was carried out in broad daylight, a departure from the past, and killed civilian bystanders. The attack immediately raised questions as to whether the ANC, in escalating its campaign, was moving away from buildings and installations toward indiscriminate civilian killings.

ANC official Ruth Mompati denies that the ANC is shifting tactics:

''It's been our policy, and still is, to hit hard targets - military and economic targets. Even in Pretoria we chose military targets. One was the South African Air Force; the other, security intelligence headquarters. These were two places we hit. We killed Air Force personnel. They were military men. We didn't hit a supermarket or concert hall where there were lots of civilians.''

The latest ANC attack, together with earlier bombings of the Sasol and Koeberg plants and rocket attacks on the center of the South African military establishment, point to an efficient and sophisticated operation.

The sudden resurgence of ANC activity is traced to the 1976 Soweto riots when African schoolchildren resisted learning the -Afri- kaans language as a compulsory subject in school. Press reports at the time estimated the number of fatalities, including children, at between 172 and 600. Thousands of politicized students fled the country and took up arms in ANC camps. They apparently pushed the leadership to take more drastic action.

Until then, the ANC was belittled in the eyes of other world revolutionaries as too comfortable and too cozy; an organization of largely middle-class coat-and-tie professionals that had little to show for the 70-odd years it had been around.

That image now has changed so dramatically that the whole destabilizing of southern Africa - triggered by sabotage within the white-ruled republic and by retaliatory raids and explosions in neighboring African states carried out by South Africa or sympathetic groups - is directly linked to ANC activity. This is because South African retaliatory attacks are directed at countries that Pretoria suspects are launching pads for guerrilla attacks into South Africa.

While the ANC has several times exposed the vulnerability of the South African security system by penetrating high-security installations like the Koeberg nuclear plant, it still faces a formidable foe.

South Africa enjoys the position of a regional superpower. Its gross national product is 10 times that of its southern African neighbors. Its Army is one of the strongest and best trained on the African continent. Living side by side with white-ruled South Africa are economically and militarily weak black African states that now know that, given a pretext, the giant next door will not hesitate to blast countries it suspects of harboring ANC groups.

On Dec. 9, 1982, South Africa struck in a lightning commando raid against suspected ANC guerrillas in Maseru, the capital of Lesotho. At least 40 people were killed. On May 23 this year South African jets attacked what turned out to be a jam factory in Maputo, Mozambique's capital. Six people were killed and more than 20 were wounded.

Both attacks, whose severity shocked neighboring African states, were regarded by many Western diplomats as overkill, particularly since South Africa has failed to provide convincing evidence of ANC military bases.

But the political lesson that South Africa intended to deliver was apparently taken to heart for most of its neighbors are showing much greater wariness now about supporting the ANC. And Mozambique, despite the Marxist character of its government, is dependent for its economic survival on South Africa.

A recent diplomatic visitor to South Africa who has closely monitored that government's political strategy suggests the following scenario on how South Africa attacked the Mozambican capital:

Word goes out from approaching South African pilots to the Maputo airport that ''We're going after specific targets not Mozambican. We're not engaging Mozambican security forces.'' After warning Mozambique to stand clear, South African jets move in. Mozambican military installations are left intact and Maputo is signaled that the raid is over. According to the diplomat, the Maputo control tower doesn't exactly come on the air and say ''thank you,'' but that, essentially, is the response.

Despite growing African reluctance to provoke South Africa, Western diplomats doubt whether African states would ever turn their backs completely on fraternal ties with the ANC. The ANC, for instance, has its headquarters in Lusaka, the capital of Zambia. It maintains a school for some 900 students in Morogoro, Tanzania. ANC refugees have been present in all the neighboring states. But South African pressure has been so evident in the last few months that it has neutralized the countries of Botswana and Swaziland, which have virtually given the ANC its marching orders to leave. Angola and Mozambique, two Marxist neighbors of South Africa, are also restraining ANC activity. Zambia's position is described as a country that accepts the political presence of the ANC, but for hard-nosed economic reasons discourages any ANC military activity.

Zambia's southern neighbor, Zimbabwe, although a Marxist state, also takes a pragmatic line and tries to keep its hands clean of military involvement with the ANC. There is an ideological reason for Zimbabwe's stand: Prime Minister Robert Mugabe is pro-Peking and until recently shunned Moscow. He has not warmed to the ANC because of its relationship with the Soviets and its close identification with Mugabe's arch rival, Joshua Nkomo, whose faction enjoyed Moscow's backing in the pre-independence struggle.

Only tiny Lesotho, to the amazement of Western diplomats, seems to refuse to get the message that it mustn't mix coexistence with South Africa and shelter for ANC guerrillas - although here, too, there are signs that Lesotho is looking for a way out.

From time to time the ANC has had training camps in many southern African states and has held mock battles in anticipation of possible encounters with South African forces. The most conspicuous training grounds have been in northern Angola, with small commando units popping up in South Africa from across several national borders.

The South African Embassy also insists there are bases in Zambia and Mozambique, but for security reasons declines to elaborate. An embassy official claims evidence was found in Beirut after the Israeli invasion of Lebanon of ANC officials given PLO military training. The ANC insists that it has no bases in neighboring countries nor does it allow its members to carry guns in these countries. The ANC has conceded that in March 1979 South African jets tried to knock out a military training school in Angola.

The heat that South Africa is applying to its northern neighbors is apparently forcing the ANC to move its camps further north. According to Thomas Karis, a professor at the Graduate School of the City University in New York City and an acknowledged expert on the ANC: ''Training goes on continually in a number of countries, but they're not in the front-line states. They're very careful about that.''

According to Professor Karis and other ANC experts, much of the training is carried out by East Germans. South African sources agree that East Germans are involved, adding that the Soviet Union, Libya, and the United Nations are prominent among those funding the ANC. The UN, which provides development and support programs, is known to fund several world liberation movements such as the ANC.

Yet preoccupation with the ANC outside the borders of South Africa begs the question of how much the ANC is a direct threat to South Africa from within South Africa.

There is some suggestion that South Africa's much publicized attacks north of its borders are calculated not only to cow the neighboring or so-called front-line states, but also to create an illusion to quiet agitated whites that the threat to their lives comes from beyond the country's borders.

The quandary as to how far South African authorities wish to admit either the number of ANC fighters who might have crossed the borders back into South Africa or the groundswell of support within the resident black population is revealed by the conflicting evidence emanating from South Africa.

In February last year the Rabie Commission for Security dismissed the threat of the ANC by saying that only a small minority of Africans belonged to the ANC. An official of the South African Embassy in Washington said the number of ANC within the country is ''very, very small indeed.'' South African military spokesmen, however, have spoken of ''guerrillas everywhere.''

How well some ANC members have been able to penetrate South Africa, avoiding detection, is provided by Tom Lodge of the University of Witwatersrand in Johannesburg. who has made a thorough study of the ANC.

According to South African press accounts, Professor Lodge cites the example of one insurgent who entered the country in 1979 and was captured only 21 months later after he was involved in attacks on police stations - at Moroka, Orlando, and Wonderboom in the Pretoria-Johannesburg area - and in the limpet mining of a power plant in Pretoria.

According to a purported classified US intelligence document, dated April 15, 1982, which came into the hands of Trans-Africa, a black American lobby group on African affairs, the ANC has 1,000 to 2,000 persons taking military training outside South Africa. The document also says there are perhaps 2,000 to 3,000 persons inside South Africa who secretly belong to the banned organization.

A number of African experts pressed on this point say that nobody is sure about ANC numbers, but a general consensus is that with 1976 riots in Soweto some 4,000 to 6,000 young Africans fled South Africa and enlisted with the military wing of the ANC outside the country's borders. Estimates put the number of ANC guerrillas outside South Africa at upward of 5,000.

Despite these acts of sabotage, Gwendolen M. Carter of Indiana University, a longtime observer of the southern African scene, believes that the ANC is more concerned with ''winning the hearts and minds'' of the black population than scoring military victories.

Says William J. Foltz, professor of political science at Yale University: ''What is of interest is not the number of armed people they have. It is the number of people building networks and building cell structures in South Africa.''

What acts of sabotage achieve, these experts say, is to publicize to blacks within South Africa that the ANC is the one organization that is fighting the government.

To Professor Foltz, ''The ANC almost certainly represents in an aspirational sense the feeling of a large proportion of the black population.''

In 1981, an opinion poll carried out by the Johannesburg Star indicated that 40 percent of urban blacks would vote for ANC candidates in free elections. In that poll, Nelson Mandela - a charismatic ANC leader who has developed into something of a folk hero among many blacks - turns up as easily the most respected black leader.

Mandela, who eluded police for a long time and is now regarded as South Africa's No. 1 political prisoner, received a 76 percent popularity rating. He has spent the last 19 years in a maximum security cell. He receives occasional visits from his activist wife, Winnie Mandela, who has been exiled to a remote area.

Dr. Carter who was in Soweto, the large exclusively black city outside Johannesburg in February, says she saw ''ANC slogans and Mandela pictures in back alleys, which I thought was pretty daring.''

Thousands have turned out recently for funerals of ANC activists inside South Africa. On such occasions ANC adherents and supporters have blatantly waved the black, yellow, and green ANC flag and sung ANC songs even though the organization is banned.

The ANC has gradually been winning more adherents of the Black Consciousness movement. Among them is Barney Pityana, one of the founders of the consciousness movement.

In the eyes of the South African government, the ANC is denounced as a communist front that kills innocent victims. Professor Karis says he sees the organization as essentially ''nondoctrinaire. There is room for Marxists and non-Marxists and there is room for Christians.''

Although an overwhelmingly black organization, the ANC neverthless contains a small group of dedicated white communists. One such communist is Joe Slovo, who operates out of Mozambique. South African authorities believe he has masterminded numerous sabotage attacks. The ANC has an alliance with the banned largely white South African Communist Party and the South African Congress of Trade Unions.

White membership was the issue that led to the 1958 split in the ANC and the formation the following year of the rival and now largely ineffective PAC. The founders of the PAC believed pro-Moscow whites were diluting African nationalism. The role of whites, however, remains a sensitive issue in the organization. When pressed on it, Ruth Mompati of London's ANC office says: ''There is no way we can say to the whites, 'Now that we have got rid of the regime you can get out.' Some are fighting in the trenches now.''

Mr. Makatini of the ANC's UN office says the black Soweto youths who crossed the borders in 1976 ''still had a lot of reactive racism. They were anti-white.'' It took some time to change this, but it came, he said, when black youths saw there were Indians and whites fighting with them.''

So far, many analysts believe that despite obvious gaps in South Africa's security system, South Africa is a long way off from being another Northern Ireland or a Lebanon. And thus far South Africa has limited its reprisals to targets outside of South Africa.

But one American analyst of the ANC is concerned about the future if bombings become more frequent and the government is forced to take stronger measures. ''What happens if the government decides to seal off half of Soweto and make a thousand arrests every time a bomb goes off.''

That, he implied, would present the ANC with a moral dilemma in which retribution could far outweigh the crime.