JOHANNESBURG, AUG. 18 -- The carnage in black townships around Johannesburg, which have experienced one of the bloodiest weeks in South Africa's history, is a sudden extension from Natal province of the civil strife between supporters of Zulu Chief Mangosuthu Buthelezi's Inkatha Movement and Nelson Mandela's African National Congress, political analysts here say.

A decision by Inkatha three weeks ago to expand beyond its regional base in Natal and become a national political party caused the three-year conflict to expand also, say the analysts. The violence has set fire to the social fiber of Johannesburg's black townships, which have one of the world's fastest urban growth rates.

Fighting continued for the third straight day in Soweto today, sending the death toll in the largest of Johannesburg's black townships to 63, with 314 people injured. Another seven were killed in Thokoza township, southeast of the city, where severe fighting took place Wednesday and Thursday.

For the second time in three days, troops were moved in to reinforce police units in an attempt to quell the fighting.

Meanwhile, in another development today, 600 heavily armed white extremists took up positions along the route of a black political march through the Orange Free State mining town of Welkom.

The extremists had vowed to react with violence if any whites were harmed during the march, but a heavy contingent of troops and police kept the two groups apart. Police said the only incident occurred when a white extremist with a crossbow fired an arrow that struck a black marcher in the arm.

The arrow's feathers were yellow, green and black, the colors of the ANC, police said.

As the civil strife fans through the packed migrant-worker hostels and teeming squatter camps where newcomers to the Johannesburg metropolitan area live in swelling numbers and deepening poverty, it poses a new and unexpected threat to President Frederik W. de Klerk's delicately balanced process of negotiating with black leaders an end to the apartheid system of racial separation.

Already voices are being raised in the security establishment for a return to the state of emergency that de Klerk lifted last month. If that happens, some observers fear that the ANC might rescind its suspension of armed struggle, and the negotiating process could begin to unravel.

Amid the charges and countercharges about who is at fault, one thing stands out: The extension of the conflict between Inkatha and the ANC beyond Natal's borders dates from Inkatha's transformation from a Zulu "cultural and liberation movement" into a conventional political party seeking nationwide support. With that change, Inkatha began a recruitment drive beyond its home base of Natal.

The relaunching began July 14. Eight days later, violence erupted in Transvaal province where 29 people were killed in fighting between Inkatha and ANC supporters in Sebokeng township, south of Johannesburg.

Fighting broke out in Soweto on July 25; in Kagiso township, west of Johannesburg, Aug. 5; and in the eastern Transvaal town of Ermelo, Aug 11.

Two days later, this week's huge eruption began, first in Thokoza township, 15 miles southeast of Johannesburg. From there it spread to neighboring Kathlehong and Vosloorus before leapfrogging over the city to Soweto once again. At week's end, 234 people were dead and about 1,500 injured.

What is also evident from a tour of the troubled areas is that the violence has centered on large migrant-workers' hostels and sprawling squatter settlements, where thousands of newcomers to the city live. Those areas present scenes of devastation, while the more established sectors of the black townships are almost untouched.

Such scenes indicate that the conflict is primarily among the newcomers -- ill-educated, rural people still close to their tribal roots.

South Africa is in the midst of sweeping urbanization, proceeding at one of the fastest rates in the world as the combination of black population growth and the collapse of apartheid's restrictions sends thousands of people streaming to the cities from the poverty-stricken tribal "homelands." The homelands are areas set aside by the ruling white government as nominally independent regions for the country's majority blacks.

When the blacks arrive in the city, they have nowhere to live because the provision of black urban housing was limited under the apartheid system, which was based on the fantasy that all blacks eventually would return to the homelands. So they have put up their own rudimentary shelters of cardboard, corrugated iron and plastic sheeting, forming crowded squatter camps where living conditions are primitive and stressful.

The hostels, meanwhile, are large, barrack-like quarters that accommodate men who have come from the tribal homelands on short-term work contracts and have left their families behind.

Tensions within the single-sex hostels, which are often compartmentalized on tribal lines, and between hostel-dwellers and the squatters, often run high. The squatters, many of whom are unemployed, regard the temporary migrants as usurpers of jobs that should be theirs.

Into this social tinder came sparks from the Natal conflagration when Inkatha began its recruitment drive a month ago.

Lloyd Vogelman, director of the Project for the Study of Violence at Johannesburg's Witwatersrand University, notes that a large proportion of migrant workers are Zulus from Natal, and that they bring the fears and hatreds of that province's long civil violence into the Transvaal hostels.

Those feelings become hardened in the hostels, according to Vogelman. "The shared living experience and strong conformity pressures there produce an extreme sense of group identity and grievance," he said in an interview.

The hostels are also places that lend themselves to easy political organization and manipulation. "There are a lot of people living in one place, so it is much easier to organize meetings and make plans for collective action than it is out in the community," Vogelman said.

He added that because there is virtually no privacy in a hostel, there is no place for a dissenter to hide. Instead, there is every chance that breaking ranks will lead to reprisals.

The ANC and its allies, pointing to a recent opinion poll showing that Inkatha had only 2 percent support among blacks outside of Natal compared with 84 percent within the province, allege that Inkatha began a campaign of enforced recruitment in the hostels after its July 14 relaunching. They claim that recruiters threatened dissidents with reprisals if they did not join Inkatha.

Inkatha spokesmen deny those allegations, charging in return that the ANC initiated the violence against Inkatha supporters because it is unwilling to tolerate political competition.

Independent verification of either claim is impossible in the present climate of pervasive fear. What is clear to observers is that the hostels have been the central points in the battles that followed. Zulu supporters of Inkatha have held councils of war in them. Then, wearing red headbands to identify themselves and carrying a crude array of weapons -- from butcher's knives, axes and sharpened iron bars to homemade shotguns with barrels cut from iron piping -- they have marched out to attack their perceived enemies.

The worst of those attacks, last Wednesday and Thursday, were directed at two squatter settlements called Phola Park and Crossroads, in the Thokoza-Katlehong-Vosloorus complex. Refugees from those settlements say the attacks occurred because dissidents from the hostels had fled there to escape reprisals from the Inkatha Zulus, who pursued them.

As the settlements were plundered and set on fire, thousands of people fled into the surrounding countryside to escape the carnage. Some stumbled into a nearby swamp and drowned.

Pro-ANC youths then mounted revenge attacks on the hostels, hurling gasoline bombs and hand grenades into them. For the next two days, gangs from both sides roamed the streets attacking one another and anyone who got in their way.

ANC sources claim that the hostel dwellers were driven by more than just recruitment zeal. They say they have evidence of an orchestrated campaign to spread a "psychosis of fear" among the Zulus living there.

According to those sources, men claiming to be Inkatha leaders went from hostel to hostel warning Zulus that they were about to be attacked and that they should join Inkatha as the only way to protect themselves.

Pallo Jordan, the ANC's information chief, showed reporters what he said were counterfeit ANC pamphlets calling for the destruction of Zulus and their exclusion from work in the Johannesburg area. He said the pamphlets were distributed in a Soweto hostel last Thursday.

The effect, Jordan contended, was to provoke the Zulus into launching preemptive attacks on the non-Zulus they thought were about to attack them.

Jordan said he suspected that "elements of the state's security services" opposed to de Klerk's reforms were behind the campaign to destabilize the negotiation process.

The ANC also accused the police of siding with Inkatha in the fighting. It has statements in writing from witnesses saying they saw the police stand by and allow heavily armed Inkatha groups to attack, then intervene only to fire tear gas at the defenders when they gathered to counterattack.

The ANC and its allies issued statements Friday bluntly accusing the police and Inkatha of jointly launching "an orchestrated campaign of terror" in the region.

Their aims, the statements said, were to destabilize an ANC stronghold area, give the impression that Inkatha had significant support outside Natal and provoke a backlash among whites and blacks who would support tough repressive measures that would undermine the negotiation process.

The police deny those charges,insisting that they are striving to be impartial in a difficult situation.

Zulu Chief Buthelezi issued a statement today from his headquarters at the Natal provincial town of Ulundi Natal, blaming the violence on the ANC and its allies, whom he accused of creating an atmosphere of tension by repeatedly insulting and attacking political opponents.

"Active attempts to isolate Inkatha and {me}, by calling for stayaways {strikes} and marches which target us, have resulted in increased tension and unnecessary conflict," he said.

"Clearly such action is provocative, and until respect for one another is observed, it will be difficult to obtain peace," Buthelezi said.