A young man stood on a bench outside a cluster of simple but fastidiously neat buildings in this tribal reserve today and blew a series of quavering notes on an antelope horn.

It was the traditional call to arms for the men of the local Pedi tribe, and this was the second day in a row it was sounded across Moutse's crowded villages. The men were being summoned to defend the chief's kraal in bitter fighting that has broken out between the Pedi and armed groups from a neighboring tribe, the Ndebele.

At least 20 persons were killed in the fighting yesterday, and the atmosphere today was tense as both sides were on alert again.

Burned-out vehicles litter the roadside in Moutse's main settlement of Kwarilaagte. Several stores have been gutted. Dark bloodstains on the roadway leading to the chief's Great Place mark the spot where two Ndebele invaders were stoned to death.

Local people predicted there would be more trouble over the weekend when workers return from their jobs in nearby towns and cities. Some observers fear the conflict could result in the most bloodshed South Africa has seen in its 16 months of racial violence.

The conflict reflects complex intergroup tensions generated by South Africa's apartheid system of segregation. Until recently Moutse was one of the most placid regions in the country. It did not figure in the widespread unrest of 1976, nor in that which racked many parts of South Africa last year.

But last August, the government announced that Moutse was to be transferred from the Lebowa tribal "homeland," which opposes independence, to the newly created KwaNdebele "homeland," which has agreed to become nominally independent of the Pretoria government this year.

Most of Moutse's 120,000 people oppose the transfer, but the white minority government in Pretoria insisted that it take effect from Jan. 1.

This is what has triggered the fighting. According to people interviewed in Moutse today, hundreds of armed Ndebele tribesmen who support the KwaNdebele government of Chief Minister Simon Skosana raided the Pedi reserve yesterday in an apparent attempt to crush its resistance to incorporation.

They say the invaders, calling themselves the Imbokhoto organization -- an Ndebele word meaning a millstone used for crushing corn -- attacked homes in Moutse, killing one man, wounding several and capturing 60 people who are now being held in a community hall in the Siyabuswa, the KwaNdebele capital.

This led to the summoning of Moutse menfolk to defend their villages, and widespread fighting broke out.

According to Maredi Cheue, who has represented Moutse in the Lebowa legislative assembly, at least 17 members of the Imbokhoto groups died in the fighting.

Two policemen were also killed and two others are missing after Moutse youths set fire to a police car. Many people here accuse the police of having aided the Ndebele in the fighting.

Groups of Ndebele men carrying knives, machetes, axes and guns patrolled the streets of Siyabuswa today and several reporters who entered the "homeland" capital were threatened.

A CBS Television crew who began photographing some of the people imprisoned in the community hall was menaced by a large group of armed men, headed by the homeland's interior minister, Piet Ntuli. The television crew was forced to leave the sprawling makeshift town.

One of the crew said later that some of the prisoners appeared to have been beaten.

Cheue said in an interview that the Imbokhoto groups had gone on a rampage of beating and looting starting at 4 a.m. yesterday.

He said they chopped down the doors of villagers' houses with axes, beat people up, smashed furniture and stole money, radios, clothing and jewelry.

"Women and children fled into the hills," Cheue said.

Chief T. G. Mathebe, traditional leader of the Moutse community, told a group of reporters he had visited the local police chief recently to tell him he feared attacks by Ndebele groups. According to the tribal leader, the police chief replied that his job was to protect white civil servants in the area.

Speaking through an interpreter, Chief Mathebe added: "Our relations with Pretoria are so bedeviled that since yesterday we feel we have reached the point of no return."

Another local community leader, Godfrey Mathebe, who also represented Moutse in the Lebowa legislative assembly, accused the homeland's leader, Cedric Pathudi, of "selling us out."

"I used to support him, but not anymore," Mathebe added, revealing another dimension to the tensions of the incorporation issue.

Mathebe, who runs a bar, was holding a meeting with other community leaders in his establishment when reporters called. Armored personnel carriers full of police patrolled past the bar as he spoke, but the police did not come in.

Conversation in the bar reflected the anger of the once placid local community. "People here would rather die than be incorporated," said Abraham Nkudi, who runs a general store in the reserve.

Lazarus Shaku, headmaster of the local high school, said the entire staff of his school had refused to sign documents transferring from the Lebowa to the KwaNdebele education department.

"If they try to force us, we'll burn our salary checks," he said defiantly. "And the students certainly won't accept it. If they try to force them, there'll be another 45,000 black youths out on the streets demonstrating."

"Why are they doing it?" asked Godfrey Methebe, referring to the Pretoria government. "Botha says he is abolishing apartheid, so why is he pushing for another independent homeland? He says he has ended forced removals, so why is he forcing us to join KwaNdebele?"