To the junior partners in the law firm of Mxenge, Ngxingweni and Shezi, 43-year-old Victoria Mxenge was, as they put it, "more of a mother than a senior colleague."

So warmly did they feel about her that they decided she should not travel alone to and from work when they were alerted by the civil rights organization to which they all belonged, the United Democratic Front, that it had been told of an assassination squad with a hit list of black activists.

There was good reason for their concern. Four years ago Mxenge's husband, Griffiths Mxenge, the founder of the law firm, was stabbed to death by assassins on his way home from the office. The men in the firm decided someone should drive Victoria home each evening.

That is how there came to be a witness to her brutal slaying as she stepped from a car outside her hilltop home in Durban's Umlazi township on Aug. 1.

The man who accompanied her that night, Mcebisi Xundu, is a minister and a friend of the young lawyers. He said that four burly black men brushed past his car as Mxenge stepped out with an armful of parcels. Xundu remembers how she screamed and ran before they shot her down and then split her skull open.

"Whoever did this, we are satisfied they are operating with the protection of the system," Xundu said.

It is a view that is widely held in the black community, although bitter and violent confrontation has occurred between black groups in the Durban area during the past few years. Some people think Mxenge could have been a victim of political infighting among blacks, while others insist that the government is involved.

A wave of anger at the Mxenge slaying has sparked rioting in the townships around Durban, which had been relatively free of the unrest spreading through much of South Africa.

The white authorities angrily deny any complicity or cover-up. "I don't protect murderers, and if I find this one, I'll lock him up even if it's President Reagan or my own mother," said Brigadier John F. van der Westhuizen, chief divisional detective officer for the Port Natal Region.

Black activists nevertheless point out that there have been a string of mysterious killings of radicals, both black and white, during the past eight years, together with a number of lesser acts of intimidating violence.

To date, no related arrest has been made by a police force that has a high success rate in capturing guerrillas of the black underground.

The Detained Persons Support Committee, an organization monitoring police actions under the stringent security laws, reported last month that six persons had been found mysteriously killed and another 27 had disappeared since the unrest began in September.

The dead include Matthew Goniwe, one of the country's most effective political organizers. The charred and mutilated bodies of Goniwe and three companions were found at a roadside near Port Elizabeth on June 27.

No arrest has been made in that case, nor in two other similar cases near Graaff-Reinet in eastern Cape Province and Duduza township, east of Johannesburg.

The government has denied complicity in the death of Goniwe. His friends have implied that they might have been victims of rivalry between black groups in eastern Cape Province.

Violent clashes have occurred between members of the multiracial Democratic Front and those of the Azanian People's Organization, which eschews white involvement in its campaign against apartheid.

The killing of Victoria Mxenge also has taken place against a backdrop of infighting between rival groups in Durban townships, blurring the activists' accusations of official complicity.

Trouble flared between black radicals and members of Chief Gatsha Buthelezi's more moderate Inkatha movement five years ago, when Buthelezi welcomed a government announcement that it intended to incorporate some of the townships in his KwaZulu tribal homeland.

The radicals, to whom the tribal homeland system is anathema, protested.

A few years ago, they formed a Joint Rent Action Committee to fight a rent increase. An opinion taken in one of the townships, Lamontville, showed that a majority supported Jorac, as the action committee is called, against the position taken by Inkatha.

This incensed Buthelezi, who has his power base among the Zulu tribe of the area. He accused the township Zulus of disloyalty. Jorac and Inkatha supporters have engaged in periodic bloody clashes ever since, and when the action committee became an affiliate of the umbrella United Democratic Front last year, the conflict widened.

Victoria Mxenge and Xundu were at the center of this conflict. Just two weeks before Mxenge's death, a group of Inkatha supporters attacked Xundu's church in Lamontville, which Democratic Front groups use as a meeting place.

"It could have been Inkatha supporters who killed Victoria," Xundu conceded, but he added that if it was, "they must have known that they had the protection of the system."

Xundu is not the only one who thinks the system is responsible, and so Victoria Mxenge takes her place beside Goniwe in the pantheon of black martyrs honored as victims of apartheid.

Ironically, just two weeks before her own death, Mxenge hung a poster of Goniwe above her bed. Distributed at Goniwe's funeral, the poster says: "Stop apartheid killing."

Mxenge, a nurse, was working in an Umlazi clinic when she met her husband, then a law student at Natal University. They married in 1964.

Soon afterward, Griffiths Mxenge was sentenced to nine years in prison on Robben Island, South Africa's Alcatraz for political prisoners, for supporting the outlawed African National Congress.

He completed his law studies in prison, and upon release, he set up his practice in Durban, where he soon established himself as a specialist in defending black activists.

Victoria Mxenge quit nursing and joined her husband as a clerk. She began studying law and, when she qualified in 1981, became a junior partner in the firm.

Just 10 months later, the Mxenges left the office together but drove home in separate cars. He never arrived. The next morning his mutilated body was found dumped in a cycling stadium with 45 stab wounds.

Victoria Mxenge took over the practice, modeling herself on her husband and quickly establishing an equal reputation as a vigorous defender of prisoners held on political charges.

She was working to defend 22 United Democratic Front leaders charged with treason the night she was slain.

Xundu, who witnessed the killing, said he decided to race for the police station a mile away. On the way he met a police patrol van with three men in it. "I stopped them and told them what was happening," Xundu said. "They replied that they were not equipped to handle the situation and that I should go on to the police station.

"When I got to the station, it took six or seven minutes before some armed detectives got in a car and headed for the house. I followed them. By the time we got there Victoria's body had already been taken to the hospital."