Namibia's militant black nationalists pledged yesterday to escalate their guerrillas war in the south-west African territory and "Liquidate" any black African government elected there under South African auspices.

Reacting to Prime Minister John Vorster's statement Wednesday that South Africa would go ahead with its own elections in November, the vice president of the Southwest African People's Organization (SWAPO) Mishake Muyongo, said his group would "never" participate in them. "Instead, we will intensity the armed struggle and liquidate whichever puppet regime Pretoria is going to install in Namibia," he declared.

At the same time, Muyongo said SWAPO would assert its right to call upon friends," especially the socialist countries," to provide it with "wll-out military assistance" so it could "effectively wage the war to its logical conclusion."

The Namibian nationalist group already has several thousand guerrillas being trained and armed by the Soviet Union and Cuba at bases in Angola. It now seems a certainty that the two communist powers will step up their aid to SWAPO, possibly including the defense of its Angolan bases. This would greatly increase the risk of a confrontation between them and South African forces. The South Africans already have raided a number of times into Angola to retaliate for guerrilla attacks on the territory.

Muyongo said he was speaking on behalf of SWAPO President Sam Nujoma and read a prepared statement indicating that what he said was official policy. He spoke at a press conference at the Namibia Institute here accompanied by a dozen members of the SWAPO Central Committee and a hundred students singing freedom songs and demanding to be sent to the warfront.

Pictures of Fidel Castro, Samora Machel of Mozambique and Aghostinho Neto of Angola were hanging on the wall behind him.

In pledging to carry out a "protracted war of national liberation" in Namibia, the SWAPO vice president said he was fully aware of the regional and international implications of such a confrontation with South Africa.

He called upon all friendly countries to render "concrete and effective support" to Angola and Zambia to help defend them against South African attacks on their territory if the war escalates.

He also asked the United Nations and the Organization of African Unity not to recognize any African government that comes to power as a result of the South African-sponsored elections in Namibia, scheduled for Nov. 23.

Muyongo said South Africa had now closed all doors to a peaceful settlement to the Namibian dispute and had itself "closen the warpath" against SWAPO.

Pretoria has administered the lightly populated but minerally rich territory, which it calls Southwest Africa, since the end of World War I under an old League of Nations mandate. Its only territorial claim there is to the port, Walvis Bay, which SWAPO and the United Nations regard as part of Namibia.

In April 1977, South Africa began negotiations with five Western powers - the United States, France, Britain, West Germany and Canada - for an elections that would be supervised and therefore recognized by the United Nations. Pretoria finally agreed last April to the plan, but after the U.N. Security Council amended it, South Africa on Wednesday announced it would no longer go along.

Muyongo accused South Africa of having followed "a double strategy" all along. He said that while it had engaged in talks with the five Western powers, South Africa had done so to buy time "to completely militarize the country by building additional bases and also by bringing in more troops into Namibia."

He said SWAPO had always expresssed serious doubts about the chances of the Western-sponsored negotiations, but had gone along after close consultations with the five front-line African states and the African organization.

Muyongo said SWAPO had repeatedly made it clear that it was only prepared to participate in elections against its South African-backed political enemies if they were supervised and controlled by the United Nations.

"For us, United Nations supervision and control meant the capacity to neutralize, demobilize, control and supervise the withdrawal of the South African trigger-happy troops," he said, "and to also monitor the activities of the police force in order to create conditions conducive to fair elections."

Meanwhile, at the United Nations yesterday, the OAU called for tough economic sanctions, including an oil embargo, against South Africa because of its rejection of the U.N. proposals for Namibia, Reuter reported.

Security Council members are to resume consultations on Monday on the question with the five Western states.