Johannesburg — The past week's violence in southern Africa is only the latest symptom of the sharpening polarization here between black nationalism and the white South African government.
With most black political activity carefully controlled or stifled, a growing number of blacks in South Africa are beginning to see violence as perhaps the only way to achieve their nationalist aspirations.
Strongest evidence of this is the ascendant support in this country among blacks for the banned African National Congress (ANC) - the group that took responsibility for the car bomb that exploded in Pretoria last week, killing 18 people and wounding about 200 others.
Some avenues of black dissent remain open in the trade unions, churches, press, community organizations, and homeland structures. And the government has also permitted a number of black political groups to operate that align themselves with the tradition of the ANC, if not the organization itself.
But most of these avenues are strictly limited. Many blacks feel politically impotent. And political analysts here believe this explains the deepening support for the ANC. The government's military rather than political response to the Pretoria bombing - an air attack on alleged ANC bases in the suburbs of Mozambique's capital, Maputo - does not encourage such analysts.
Another factor is the apparent lack of success of black ''moderates'' - or those still willing to work above ground - in gaining significant concessions from the government. Zulu homeland leader Gatsha Buthelezi's Inkatha movement, for instance, is criticized by some other blacks for getting nothing but the back hand of the government, even though it boasts a membership of over 750,000.
The South African government's main task in its own words is ''the synchronization of black and white aspirations within the country.'' But the credibility of the ANC among many blacks suggests the government's efforts to encourage blacks to work ''within the system'' are failing.
There remains a glimmer of hope, often expressed most passionately by blacks who continue to eschew violence. One such person is Bishop Desmond Tutu of the South African Council of Churches.
''Many now think the only language the government understands is force. But if there were a genuine inclination of wanting change by the government there would be a willingness of blacks to participate,'' he says.
The root of the problem, suggests Tom Lodge, a political scientist whose speciality is black politics, may be that ''the government basically sees all black groups as subversive.'' This leads to excessive hostility and repression, he adds.
''The government has cleared the middle ground'' in South African politics, perhaps unwittingly encouraging the polarization that seems to have made violence the only answer for a growing number of blacks, says Lodge.
Can the growing black nationalist challenge to white rule be channeled, nonetheless, into dissent that would be ''legal'' and nonviolent - and yet, from the black point of view, effective?
Or is the line of dissent drawn so rigidly by Pretoria that black grievances can only find expression through bombs?
Much of South African society today seems to accept that the rising tide of violence has reached the point of no return. The government says it will meet force with force. South Africans were told this week by the government-controlled television service that ''Northern Ireland has come to South Africa.'' The message: Hunker down and get ready for the onslaught.
The nub of the problem and one reason the conflict has spread beyond the bounds of conventional political dissent appears to be the diametrically opposed starting points of those involved. Black activists seek enfranchisement in a unitary South Africa, which implies majority rule. The white Afrikaner government rules that out as ''non-negotiable.''
Still, history shows that the spirit of the black nationalism in South Africa is sensitive to the policies of the government. In the view of some analysts, that spirit has hardened over the years with what blacks see as continuing efforts to exclude them from any meaningful political role.
The founding of the Union of South Africa in 1910 did not include enfranchising blacks nationally. Two years later the ANC was founded. In the 1950s, after the National Party came to power and introduced a number of apartheid laws, civil disobedience campaigns were started by blacks.
South Africa became a republic in 1961, but its new Constitution continued the exclusion of blacks. Shortly thereafter the ANC, banned a little earlier, explicitly embraced violence as a tactic. (The ANC maintained that it had promoted peaceful change since its founding, but that approach had not worked and therefore it decided violence was its only option.)
South Africa is again on the verge of adopting a constitution that would continue to exclude blacks, even though it gives a new political role to Indians and Coloreds (people of mixed race). Some analysts feel the dramatic new turn in violence may be in part a response to the new constitution.
The limits of dissent in South Africa fluctuate, depending on circumstances. Advocating violence or supporting it, and promoting communism are outlawed.
But beyond that, the government is inconsistent in what it tolerates as legitimate criticism and pressure for change.
In general, it appears the government is less hostile to black political dissent that comes from individuals or organizations operating within its apartheid framework. Homeland leader Buthelezi is a prime example (even though he has rejected the ''homeland'' structure).
''At times Buthelezi's rhetoric is indistinguishable from the ANC, but he has a freedom of speech not accorded to blacks without his (homeland) base,'' says one informed political observer.
Also, it appears that while the laws used by the government to control dissent apply to everyone, they are most vigorously enforced against the black community. In the view of many analysts, this is because the main standard of whether dissent is tolerated or not is its effectiveness, and white dissent always has a fairly limited audience.
Says Bishop Tutu: ''The government will allow any opposition they know is going to be ineffective. It is when you have a lever that will change rhetoric into action that they step in.''
One of the first things visitors to South Africa notice is the often sharp criticism of the government in the English-language press. South Africa has a freer press than one finds in much of Africa.
Prof. John Dugard, a legal expert at the University of the Witwatersrand, says criticism in the white press is acceptable because it is not seen as threatening. However, ''any black paper operates in a very delicate situation.'' Since 1977, security laws have led to the closing of two black newspapers.
Black political organizations per se are not outlawed. But they are virtually nonexistant on a national, broadly based, nonethnic scale, due in part to many government-imposed restrictions.
Structurally, there is no place for such a party in the legal framework of South Africa. Blacks have no representation in Parliament. And the government has done everything in its power to foster the segmentation of blacks into ethnic groupings.
Multiracial political parties are outlawed in South Africa, meaning blacks cannot look to some white political group for expression of grievances in Parliament.
Absent any normal political vehicle for expressing their views, blacks in the 1950s launched a passive resistance campaign. But in 1953 the government passed a law providing for stiff penalties for those who break even minor laws as part of a campaign of protest, or who incite others to participate. Passive resistance has since disappeared as a protest vehicle.
Other inhibitions against black political activity are contained in security laws that give the government wide latitude in shutting off dissent. South Africa's newly consolidated internal security act permits prosecution for acts ''calculated to endanger the security of the state.''
Beginning in the 1960s, the government responded to more overt black resistance with tougher restrictions on individual freedoms. Persons can be detained indefinitely beyond the reach of the courts. They can be banned - meaning they cannot meet people except one at a time and cannot be quoted in the press - for reasons never explained by the government.
A prohibition on all outdoor meetings imposed in 1976 hits blacks particularly hard since they have less access to indoor facilities.
The mounting restrictions on dissent over the years is explained by the government as being provoked by the subversive activities of the Communist Party. Communism was outlawed in 1950. But some adherents later infiltrated the ANC, formed the Pan Africanist Congress, and instigated riots leading to the banning of both groups in 1960, according to the government.
In the political vacuum left, the ''black consciousness movement'' took root in the late 1960s. Its leaders and main organizations were banned in 1977. (Principal black consciousness leader Steve Biko died in police custody.) The government says its action was provoked by the violence the movement triggered in 1976.
The two most significant political developments for blacks in recent years have been attempts in black townships to organize community-based groups, concerned primarily with local issues, and the gathering strength of black trade unions.
Developments in the trade-union field are considered progressive, even by government critics. Tom Lodge says black unions have been discouraged by the government from any political affiliation. Still, he says the government's allowing blacks to form unions ''does involve a significant concession of power.''
While black unions are gaining in strength, the better organized ones seem eager to avoid overt activity in politics and to focus more on traditional labor issues.
Churches also have been given some latitude to sharply disagree with the government. A number of churches have declined to obey the government law prohibiting multiracial marriages. The South African Council of Churches (SACC) has declared apartheid heresy. Government tolerance of dissent within the churches could be affected by the present investigations of the so-called Eloff Commission into the SACC.