JOHANNESBURG, DEC. 27 -- Despite an impassioned appeal by Anglican Archbishop Desmond Tutu for a suspension of violence, eight people were reported killed today in factional fighting in black townships in Natal Province, bringing to 13 the total dead over the Christmas weekend in internecine clashes.

It was one of the most violent weekends this year in Natal, where street warfare between rival black groups has resulted in the deaths of more than 200 people in the past two months alone, most of them in townships around the provincial capital, Pietermaritzburg.

Tutu, winner of the 1984 Nobel Peace Prize, today called the latest wave of violence "a ghastly spiral of unending revenge killings."

In his first public statement on the fighting since unsuccessfully trying to mediate between rival factions on Dec. 6, Tutu said, "The shocking carnage in Pietermaritzburg has to stop. The absolute minimum condition necessary as we enter 1988 is an immediate cease-fire -- a complete suspension of all violence while the peace talks are under way."

Tutu was sharply critical of leaders of the conservative Inkatha movement, headed by Zulu Chief Mangosuthu Gatsha Buthelezi, and the militant United Democratic Front, a coalition of 700 antiapartheid groups, which is loosely allied with the outlawed African National Congress.

The archbishop said that instead of ordering their followers to implement an immediate suspension of vengeance attacks, the rival groups' leaders continue to engage in "aggressive verbal political attacks" that fuel fighting in the streets.

"Political organizations appear to envisage the violence ceasing only after and not before they have achieved a settlement of their political differences. This creates the clear impression that they regard violence as an instrument to achieve political objectives," he said.

The South African Police Department's daily report said four blacks were killed today in clashes around Pietermaritzburg, the scene of the most intense factional fighting, which began two years ago in Natal Province and has increased in recent months.

Authorities reported that two blacks were killed and seven injured at the Molweni township, near Durban, when fighting erupted between families and friends of a murder victim and those of his alleged assailant.

Police officials said 22 houses were set on fire during the Molweni incident and that security forces dispersed crowds with rubber bullets, tear gas and shotgun fire. They said 43 people were arrested.

The authorities said two other men were killed in a clash at Taylor's Halt, near Pietermaritzburg, and security forces there had to disperse a mob with tear gas. In the same area, police found the body of a black man with stab wounds.

Officials said a black man was burned to death at Magwanyani, near Pietermaritzburg, and that another black man was shot to death when he attacked a policeman in Kwamashu, near Durban.

Yesterday, the police reported five persons killed in factional fighting in Natal, four of them around Pietermaritzburg.

The fighting is part of a two-year struggle for dominance in the townships that turned violent most recently after an Inkatha recruitment campaign in which UDF leaders charged that Inkatha zealots were press-ganging people into joining the movement.

Inkatha leaders charged that the UDF, allied with the black labor union umbrella, the Congress of South African Trade Unions, tried to disrupt its membership drive.

Both sides say they resort to violence only in self-defense, although some Inkatha leaders have endorsed vengeance killings. Buthelezi recently said he could not be held responsible for the actions of every one of more than one million members of his predominantly Zulu movement.

Repeated attempts to hold peace talks between the two groups have collapsed, partly, UDF leaders charge, because security police have detained without trial scores of UDF local leaders who were to take part in the meetings.

Although both groups oppose South Africa's apartheid policy of racial separation, they differ widely in political philosophy and tactics. Inkatha opposes economic sanctions against South Africa and advocates negotiations with white leaders in Pretoria under certain conditions, while the UDF is more militant.

Since the resurgence of black violence in South Africa in September 1984, more than 2,500 people have been killed nationwide, a majority of them in black-against-black violence.

The fighting has wide implications for the future of power-sharing in South Africa, because it appears to reinforce assertions by many white conservatives that tribal and political rivalries among blacks would make a unitary system of one-man, one-vote untenable and lead to a breakup of the country.

Tutu said the Natal violence was generated by the maintenance of "hard-core apartheid," which he defined as the exclusion of blacks from political power.

Apartheid "denies black political groups the logical and peaceful way to test their political support, through the ballot box, and transfers conflict to the streets," he said.