Clemens Kapuuo, chief of the Herero people and president of a multiracial political party in Southwest Africa (Namibia) was assassinated last night as he stood talking to friends outside his general store.

His death has raised fears of an outburst of fierce intertribal fighting in the South African administered territory. It is also expected to have serious repercussions on current negotiations between South Africa and the black guerrilla movement, the Southwest Africa Peoples' Organization SWAPO leader Sam Nujoma in to independence by the end of this year.

Under the proposed settlement, Kapuuo, who was 55, would have been the Principal Political rival of exiled SWAPO leader Sam Nujoma in United Nations-supervised elections to set up an independent government.

South Africa, which has administered Namibia since the end of World War II, has accused SWAPO of wanting to set up a "Marxist dictatorship" in the territory and is hoping that Kapuuo's moderate Democratic Turnhalle Alliance party will win the elections. Kapuuo then would have become Namibia's first black president.

Only six weeks ago another Turnhalle leader, Ovambo Health Minister Tiovo Shiyagaya, was killed at a political rally. The gunman was shot dead at the scene by police.

Kapuuo was shot in the courtyard of his store in the black township of Katutura just outside Windhock, capital of Namibia. He died about 45 minutes later in a nearby hospital, according to Brig. Gen. Victor Verster, divisional commissioner of police for Namibia.

A manhunt is underway for the two assailants, who were hiding behind the wall surrounding Kapuuo's store and who ran after the shooting, Verster said.

South African Foreign Minister Pik Botha said:

"The South African prime minister and his government are deeply shocked by this latest cowardly murder of a prominent leader of Southwest Africa . . . [who] gave his life for his country and his people. He was a true leader of Africa."

Police Commissioner Verster said there were signs of tension in Katutura and authorities were anticipating an outbreak of fighting between the Hereros and the Ovambos, the largest tribal group in the country and traditional supporters of SWAPO.

The black community of Katutura was gripped by fighting between the two tribal groups earlier this month in which 14 people were killed and more than a hundred were wounded.

Negotiations between South Africa and SWAPO, mediated by the United States, France, Britain, Canada and West Germany, are nearing an end. Few differences remain, although there are suspicions on both sides.

One of the reasons for the weekend visit to Zambia by Andrew Young, the U.S. Ambassador to the United Nations, was to seek a successful conclusion to the talks on Namibia. Young spoke with Nujoma in the Zambian capital.

South Africa has been warning for several weeks that the political and military situation in Namibia was "deteriorating" as the talks dragged on. Two weeks ago the government gave widespread publicity to a document it said was acquired from a SWAPO base in Angola which included plans to assassinate non-SWAPO black leaders inside Namibia.

There is no indication, however, that SWAPO is responsible for Kapuuo's death.

Dirk Mudge, a former member of South Africa's ruling National Party and now the chairman of the Turnhalle Alliance, said he did not wish to blame any political group for the killing.

Nevertheless, political observers believe that Kapuuo's killing will be exploited by those within the South African government who do not want any settlement that includes SWAPO. They can be expected to call for breaking off the talks.

Prime Minister John Vorster and Foreign Minister Botha have come under increasing pressure from whites in Namibia and from members of their own party to go ahead with a so-called internal solution by holding elections without SWAPO.

South Africa has not done this until now because of threats that it would trigger U.N.-imposed trade sanctions.