ARUSHA, TANZANIA -- The African National Congress, the main guerrilla force battling white-minority rule in South Africa, is preparing to launch a major campaign for international recognition as the "sole, legitimate representative" of South Africa's black-majority population.

Propelled by growing signs that negotiations with the Pretoria government for power sharing could become a reality in the not-too-distant future, the campaign will be aimed at obtaining some level of diplomatic recognition by a number of countries and a seat in the United Nations, senior ANC sources said during a four-day international conference held here last week.

Such recognition would place the ANC at the forefront of any future negotiations, ahead of the rival Pan Africanist Congress (PAC) and the moderate Inkatha movement of Zulu Chief Mangosuthu Gatsha Buthelezi.

It also would give the ANC an edge in knowing the positions of countries that might participate in efforts to reach a solution to the South African problem if a peaceful transfer of power ever becomes the object of an international negotiating forum.

"Those countries will be applying pressure on both sides, and we need to know ahead of time what they stand for," a senior ANC source said.

But the primary objective of the campaign, the ANC source said, is to press as many countries as possible to acknowledge the "illegitimacy" of the government of President Pieter W. Botha because it denies any participation by the 26-million-strong black majority of South Africa.

"There is at the moment dual power in South Africa -- the Botha regime and the ANC. If the Botha power is declared illegitimate, then you therefore have to confer recognition to whatever power is legitimate," said the ANC official, a member of the exiled group's executive committee.

The ANC leadership has been encouraged by a debate within the Canadian government on whether diplomatic recognition of South Africa's white-led government is justifiable in the face of Ottawa's condemnation of the apartheid system of racial separation as immoral.

Canadian Prime Minister Brian Mulroney has said his government is considering imposing broader sanctions on South Africa, including withdrawal of diplomatic recognition.

If that happened, ANC officials said, they would seek Canada's recognition of the black nationalist organization in place of the Pretoria government.

Currently, only the Soviet Union, Romania and East Germany have granted diplomatic recognition to the ANC, although Kenya plans to upgrade the ANC's office in Nairobi to include limited diplomatic status later this month.

Initially, the ANC is seeking only partial diplomatic status for its offices in 26 capitals, mostly in West Europe, including London, Paris and Bonn. (The ANC's U.S. office is in New York.)

This type of recognition would enable the organization to be listed in diplomatic directories, participate in national-day celebrations and gain some of the privileges accorded to embassies.

Approaches also are being made to India and to the six "front-line" black African states -- Zimbabwe, Angola, Mozambique, Botswana, Zambia and Tanzania -- for some form of diplomatic recognition, ANC officials said.

However, the officials acknowledged that Zimbabwe is problematical because of the ruling ZANU Party's historical links with the Pan Africanist Congress.

The PAC broke with the ANC in 1959.

The senior ANC source, speaking with the understanding that he would not be identified, denied that the ANC's campaign for recognition as the "sole, legitimate representative" of South Africa's blacks was intended to isolate the rival PAC.

He acknowledged that the Palestine Liberation Organization (PLO) and the South West People's Organization (SWAPO), both of which gained U.N. recognition as "sole, legitimate representatives" of, respectively, Palestinians and Namibians, subsequently had splintering problems.

The ANC official said the diplomatic campaign was the result of a strategy that evolved over two years, but that the impetus came with increasing signs in recent months by Botha's government that it is willing to talk not only with moderate blacks but also with those it regards as "radicals."

The official noted that this raised the question of who would negotiate on behalf of South Africa's blacks.

The ANC's public stance -- reaffirmed by the delegates to the conference here in a closing declaration -- is that it is too early for negotiations, because Pretoria is not interested in entering into genuine talks, and that any discussions would have to address the central question of political power and not reform of apartheid.

However, ANC members unofficially acknowledged that negotiations inevitably will occur and that the prenegotiating process should compel more countries to condemn apartheid and declared their belief in a nonracial, democratic government for South Africa.

By doing so, such countries would recognize as illegitimate Botha's government, which has said it will never agree to a unitary system of one-man, one-vote, the ANC officials said.

Citing a Sept. 29 speech by Secretary of State George P. Shultz, in which he called for universal voting rights for all South Africans, one ANC source said, "Shultz not only said what he was against, but what he was for. That's what we're asking everybody else to do."

In the conference here, ANC executive committee member Johnstone Makatini urged that South Africa, whose credentials to the U.N. General Assembly were lifted in 1974, be permanently expelled and that its seat be given to the ANC.

As the oldest black nationalist movement in South Africa -- 75 years -- the ANC should at least enjoy status in the United Nations equal to that of the PLO and SWAPO, Makatini said.