ARUSHA, TANZANIA, DEC. 1 -- African National Congress President Oliver Tambo said today there can be no peace negotiations with South Africa's white minority government until Pretoria commits itself unequivocally to black majority rule.

Tambo also said the ANC would not abandon its "armed struggle" for liberation until the South African government is ready to open real negotiations for a transfer of power to the country's 26 million blacks.

Responding to recent moves by the government of President Pieter W. Botha to remove obstacles to power-sharing talks with black leaders, Tambo said, "We are not interested in talking merely for the sake of dialogue."

At the same time, Tambo called for intensified economic sanctions to isolate South Africa further in the world community and force it to "abandon the tyranny of apartheid."

Tambo gave the opening address at a four-day conference attended by about 500 antiapartheid campaigners and government officials from 41 countries.

It is the first time the 75-year-old ANC, the dominant liberation movement in South Africa, has organized an international conference in a bid to broaden its recognition as a government in exile and to raise funds for its activities.

The theme of the conference is "Peoples of the World Against Apartheid for a Democratic South Africa," and the purpose, Tambo said, was to "shape the future" of the antiapartheid movement's strategies, particularly on sanctions.

Unlike last July's conference in Dakar, Senegal, which was organized by white opposition South African liberals, the meeting here so far has not included any black or white delegates still living in South Africa.

Speakers from South Africa were to have taken up the morning session on Wednesday. But apparently they have stayed away out of fear that their presence at a meeting run by the ANC would be regarded by South African security police as a prima facie case of furthering the aims of a banned organization.

Noting that Botha's government has repeatedly raised the question of opening talks, Tambo said, "This regime has no intention whatsoever of entering negotiations. Rather, it wants to protect and perpetuate white domination by co-opting blacks."

Tambo said there can be no political solution in South Africa until the political system is "transformed to a nonracial, one-person, one-vote, unitary state.

"Without acceptance of this perspective, there can be no negotiations. All negotiations would have to be about how to transform South Africa along these perspectives," Tambo said.

His remarks reflected longstanding ANC positions, but were significant because they were reiterated so soon after numerous signals by Botha's government that it may be willing to open talks even with black leaders it considers to be "radicals."

Among those signals was the release of imprisoned ANC leader Govan Mbeki on Nov. 6. The freeing of Mbeki has been seen as a possible prelude to the release of ANC leader Nelson Mandela and the opening of talks with the black nationalist organization.

On the sensitive question of abandoning violence as a strategy for unseating the Pretoria government, Tambo said the ANC never wanted to pursue a "path of war" against such a strong military foe.

But, he said, "Any suspension of hostilities is something that can be negotiated and agreed upon as part of negotiations to create a democratic South Africa."

An even harder line was presented in an address by former Tanzanian president Julius Nyerere, who said Pretoria's recent reform measures were designed solely to dupe blacks into abandoning armed opposition.

"We are told there are moderates who have to be supported. We are told by the Ronald Reagans and the Margaret Thatchers of the world that we should abandon the armed struggle. We are told we should negotiate with the apartheid government to get more reform," Nyerere said.

But, he added, "All these reforms are merely an attempt to confuse the people and delay the inevitable . . . All that the so-called reforms amount to is an amelioration of the prison house called apartheid."

Unfortunately, the need for the armed struggle is not over with yet, Nyerere said.

A number of public figures invited to the conference failed to show up, including Yasser Arafat, chairman of the Palestine Liberation Organization; entertainers Stevie Wonder and Harry Belafonte, and presidential aspirant Jesse Jackson.