EVEN AS Nelson Mandela has been touring the world and raising hopes for a negotiated end to apartheid, South Africa is experiencing its worst year of political violence ever. In the first six months of 1990, more than 1,600 people were killed, compared with 700 deaths in the 1976 Soweto uprising. Indeed, from 1987 to 1990 the number of deaths in the so-called "Valley of Death" around Pietermaritzburg, the epicenter of the violence, was twice the number killed in Beirut.

Stopping this violence is the most important issue on the agenda that Mandela and South African President Frederik W. de Klerk will address in their meetings next month, since it is a precondition for progress on all the other sticky constitutional and economic issues. At the core of this problem is the need to make the South Africa police do their job impartially, a need that, many suspect, has been neglected by a white power structure that sees advantage in the specter of inter-black fighting.

The worst recent incident occurred last Thursday when fighting between rival black political factions culminated in a bloody bus crash near Durban and left 26 dead and 56 injured. The incident led South African Church leaders to demand immediate action from de Klerk to stop the cycle of violence in Natal and prompted the ANC to warn it might have to turn to its own army for protection from the Inkatha forces led by Zulu Chief Mangosuthu Buthelezi.

Of course violence has long been endemic to South Africa. In a country with just 35 million people, each year there are about 10,000 ordinary murders and 15,000 rapes in addition to the hundreds shot by the police and the army or executed by the judicial system. However, the recent upsurge in political violence has different roots. It first took off in late 1983, slowed temporarily in early 1987, and then soared again. More than half of it is concentrated in the "Valley of Death" and Durban townships, and almost all of it is not interracial or intertribal, but "Zulu on Zulu."

To understand the roots of this violence I recently made several visits to Pietermaritzburg, a quaint Sleepy Hollow-style city of 150,000, 45 miles north of Durban. It borders on the beautiful red-and-green hills of Kwazulu, the homeland in Natal province designated by South Africa for the country's 7 million Zulus. It is presided over by Buthelezi, still the second most powerful black leader in South Africa. On July 14, Buthelezi announced he was converting his Inkatha organization into a multi-racial political party that would seek to block "the ANC's attempt to monopolize political power."

As I arrived in Pietermaritzburg early one Saturday in May, its white population appeared to be preoccupied mainly with the question of whether to attend a local dog show or a classic car exhibition. It is part of apartheid's perverse charm that white people can live a few miles from Beirut-scale violence and still not have it interfere with their dog shows. Just 10 miles to the north, however, on a hill in the Vulindlela region of Kwazulu, a huge all-day funeral was in progress for the eighth son of David Ntombela, the region's tribal subchief.

Ntombela, a short black man in his late fifties who wears a bullet-proof vest, is one of the five most powerful regional bosses in the 1.7 million-strong Inkatha organization and a member of the Kwazulu Legislative Assembly. He also commands a large contingent of Zulu warriors, about 2,000 of whom had turned out for his son's funeral, hoisting spears, shields, clubs, and rifles, chanting war songs, and wearing Buthelezi T-shirts marked "Victory Through Peace."

Ntombela says he is committed to peace, but not everyone believes him -- for example, a Jesuit priest was run out of town last Easter weekend because he accused Ntombela of commanding goon squads, forcing townspeople to make contributions to Inkatha, and even murdering his own brother. In 1989 an official Inquest Court found probable cause to hold Ntombela responsible for the deaths of an 11-year-old girl and her mother. The week of my arrival, his son Drake had been shot by an unidentified assassin. Ntombela says he has no idea who was responsible. But the day after Drake died, in a nearby township another unidentified gunman blasted Reverend Victor Afrikander, an executive member of the South African Council of Churches and a sympathizer with the United Democratic Front, Inkatha's arch-enemy.

For blacks in this region such funerals have become as common as thatched huts. Two weeks before the Ntombela funeral I attended another one in nearby Edendale for 15 victims killed, according to press accounts and several eyewitnesses, when Ntombela had helped to organize a massive dawn raid on UDF-leaning villages by Inkatha warriors. They broke down doors, torched and looted hundreds of houses, forced about 11,000 refugees to flee, and, over four days, killed at least 100 people. The South African Riot Police were called, but did nothing to stop the violence.

According to Ntombela, the precipitating cause of this assault was the fact that UDF supporters had stoned Inkatha buses on their way to a Durban rally. The stoning is denied by the UDF and a member of Parliament who was present. But even if it took place, it did not justify the harsh reprisal.

The epidemic of violence is rooted in a power struggle between Inkatha and the ANC that dates back at least to 1979, and, equally important, in the South African police's systematic failure to discipline warlords like Ntombela.

To many conservatives Buthelezi has always been apartheid's perfect opponent, a nonradical alternative to the ANC -- handsome and well-spoken, critical of the system, yet also opposed to sanctions and an outspoken advocate of "democracy," "non-violence," and "capitalism." In fact there is almost nothing democratic about Inkatha or Kwazulu: Buthelezi's "capitalistic" homeland is almost completely dependent on South African funding; his police are notoriously anti-democratic; and the actual size of Inkatha's "voluntary" membership has never been clear. But such ambiguities are easy to ignore, and over the years Buthelezi has attracted a crop of enthusiastic admirers in high places, including former South African President P.W. Botha, Ronald Reagan, Pat Buchanan, Alexander Haig, Jeane Kirkpatrick and Tony Bloom, the owner of a huge South African conglomerate that employs one of Buthelezi's sons.

Now in his early 60s, Buthelezi is the cousin of a former Zulu king and the son of the 10th wife of a Zulu chief. A radical in his college days, by 1951 he had become a clerk in Durban's Native Affairs Department and, after a probationary period, was confirmed in 1957 as a chief by the conservative Native Administration. Buthelezi opposed creation of the Kwazulu homeland but in 1972 became its Chief Minister Counselor.

Inkatha itself was actually founded in the 1920s as an ethic organization for Zulus, but it folded in the 1930s after an embezzlement scandal. In 1974, Buthelezi revived it, and when South Africa transferred schools, police and hospitals to the Kwazulu Government, public jobs fell under Inkatha's control.

On the basis of support from local warlords such as Ntombela, and the jobs and housing they controlled, Inkatha's claimed membership reached 400,000 by 1979 and 1.2 million by 1983.

In late 1979, several key leaders of the then-banned ANC met Buthelezi in London to discuss an alliance. According to Oscar Dhlomo, who resigned as Inkatha's General Secretary on June 1, Buthelezi refused to follow orders as the ANC expected. At this point Dhlomo thinks the ANC started to view Inkatha as a rival and look elsewhere for an internal proxy -- as of 1983 to the UDF, and later to the Congress of South African Trade Unions.

So when young UDF "comrades" began organizing school boycotts and job stay-aways in Durban in late 1983, Buthelezi perceived a challenge to his authority. One of the first violent incidents took place in 1983, when five student activists were killed by Inkatha warriors after protesting a Buthelezi speech. The incident established a pattern: young "comrades" show "disrespect," Inkatha responds with disproportionate force, and South African and Kwazulu police look the other way.

Especially after 1988, when violence in Natal escalated, many observers in the press threw up their hands and concluded that the violence was basically tit-for-tat. But a more careful study by an independent monitoring group at the University of Natal shows that the UDF got by far the worst of it -- their indentifiable dead outnumbered those of Inkatha by at least three to one -- and recently 10 to one -- and there were very few refugees or lost homes in Inkatha areas. Most of the victims had no political affiliation at all, their random deaths attributable to Inkatha's mass raiding tactics.

The other crucial fact about Natal's violence is that until recently the police have done very little to prevent it. As Mike Tarr, a white Pietermaritzburg MP, observed in April, "This whole problem could be solved if the police arrested just five people" -- i.e., the Inkatha warlords.

Instead, according to numerous sources, the police have never tried to intercept Inkatha attacks in advance. As the departing U.S. consul in Durban pointed out only two weeks ago, out of 3,300 political killings, less than a dozen have been successfully prosecuted. For example, Ntombela himself has yet to be tried on the murder charge noted earlier. Nor have two other warlords, including Inkatha's deputy minister of the interior who was charged on five counts of murder. Indeed, lawyers complain that witnesses who have filed complaints with the police are often been harassed. So some non-Inkatha people have simply lost confidence in the judicial system and turned to self-help.

There are also credible reports that the authorities have given Inkatha direct aid. For example, according to a local Catholic priest, the township Ntuzuma was attacked last December by 300 Inkatha Zulus. After three days of fighting, 25 to 30 people lay dead. Finally the South African Army arrived and picked off seven snipers. When the snipers' bodies were examined some turned out to be members of the Kwazulu police. Since 1987 the head of Kwazulu's police force, who reports directly to Buthelezi, has been Jack Buchner, a white who was the South African Security Police's leading expert on counter-revolution and the ANC.

In 1987 the mayor of Pietermaritzburg, Mark Cornell, arranged a meeting with Adriaan Vlok, South Africa's minister of law and order. According to Cornell, when he complained to Vlok about Inkatha warlords roaming the streets without being arrested, Vlok brought him up short: "Mr. Cornell, do you honestly not want Inkatha to win in Pietermaritzburg?" An MP from Pietermaritzburg got a similar response from the minister. And Vlok has also been one-sided at other times: He met privately with Buthelezi in March 1987, but refused to see the UDF; he publicly attributed most of the problem to the UDF; and he supported a UDF banning order in February 1988 that made it difficult for the two sides to meet.

More generally, this year's Harms Commission inquiry, begun in February by de Klerk, has already produced evidence that the South African police have for years been involved in systematic terrorism. For example, at least 100 mysterious deaths occurred among "above-ground" activists in the 1980s, and there is evidence that at least several were due to the Security Police. Clearly de Klerk has to walk a tightrope -- there is concern that diehard "bittereinders" in the police might try to destabilize the situation.

Meanwhile, the main parties to the Natal dispute have tried to mediate it themselves, so far with little success. Buthelezi has expressed willingness to hold peace talks with the UDF and ANC, but only if its leaders negotiate with him directly. They say he is more worried about securing a role for himself in the constitutional negotiations than about containing violence. The ANC also remains divided about peace talks -- in April 1990, Mandela agreed to hold a joint peace rally with Buthelezi in Durban, but Mandela's Natal supporters were outraged. They pointed out that Buthelezi had broken several earlier agreements to curtail violence. In early July the UDF and COSATU also held successful job stayaways in Pietermaritzburg to protest the police's one-sided conduct. Right now the ANC is planning a peace conference in Durban that excludes Inkatha.

As for de Klerk, he appears to recognize that Natal has become an obstacle to progress on other basic issues, and that his police can no longer be trusted. In April he assigned about 300 crack troops to Natal, added to 2,000 regular Army already there, and he has maintained the state of emergency while suspending it elsewhere. This month Minister Vlok also assigned several hundred more police to the region. Within a month de Klerk will meet with a high-level delegation from the ANC and the UDF to deal with the role of the police.

In the meantime violence in Natal continues. And violence, including the first important instances of white terrorism, has also been spreading to other parts of the country; for example, in July there have been two anti-black bombings and a grenade attack in Johannesburg. Surely apartheid's most bitter fruit of all would be a post-apartheid society that turned out to be even more violent than its predecessor.

James Henry, a journalist who writes frequently about developing countries, recently returned from a six-week trip to South Africa.