PRETORIA, SOUTH AFRICA, MAY 26 -- South African proponents of apartheid held the largest gathering of whites in nearly three decades today and heard Conservative Party leader Andries Treurnicht call for the ouster of President Frederik W. de Klerk and the establishment of an all-white state.

Treurnicht warned de Klerk that South African conservatives are not about to accept black majority rule "without bitter struggle" and demanded recognition for "our right to our own territory and the right to rule ourselves."

The rally, held beneath the imposing Afrikaner Voortrekker Monument on a knoll outside Pretoria, drew an estimated 60,000 right-wing and conservative whites strongly opposed to de Klerk's policies of legalizing the African National Congress and other anti-apartheid groups and opening negotiations with them for an end to the apartheid policies of racial segregation and white domination.

While the all-white crowd was smaller than the 100,000 people the Conservative Party had hoped to attract, it was reportedly the largest since the late prime minister Hendrik F. Verwoerd addressed a gathering here in 1961 after whites voted to make South Africa a republic and withdraw from the British Commonwealth.

Massed below the Voortrekker Monument, which marks the Boer trek northward from the British-ruled Cape Colony in the 1830s, the demonstrators were asked by one speaker whether they wanted de Klerk to negotiate on their behalf. "No, no, no, no," they shouted back.

The gathering, attended by many extended white families, from grandparents to small babies in carriages, was a measure of the considerable white resistance de Klerk is certain to face as he presses forward with his announced plans to phase out apartheid legislation and pursue talks with black leaders.

But the South African leader today signaled his determination not to veer from his reform course. "The new South Africa is already in the process of being born," de Klerk declared at Johannesburg airport on his return from an 18-day tour of nine West European capitals. "Nobody can stop it. Through no mustering of large meetings can anybody stop the process. We will not allow ourselves to be frightened, threatened or intimidated off this path."

De Klerk reported that he was promised that the question of lifting at least some of the economic sanctions imposed on South Africa now will be considered seriously by the European Community. It is expected to discuss the sanction issues at its next summit, June 25 in Dublin.

But de Klerk warned his followers not to expect immediate, dramatic changes in European policies. While "sanctions are crumbling" in some Western European nations, he said, others wanted to follow a joint European Community policy toward South Africa.

At another large rally in Pretoria's black township of Attridgeville, ANC leader Nelson Mandela called upon whites to support de Klerk's reform policies and accused Treurnicht of fomenting white fears and opposition to them.

Today's pro-apartheid rally came on the 42nd anniversary of the assumption of power by the National Party, which de Klerk now heads. The rally started with a procession of the colorful flags from the three short-lived 19th century Boer republics of Natal, Orange Free State and Transvaal and the singing of old nationalist songs.

Famous lines from the speeches of past Afrikaner presidents and prime ministers since the National Party came to power in 1948 were rebroadcast in their orignal voices. The voice of the immediate past president, Pieter W. Botha, was omitted, apparently because he is blamed by the Conservative Party for the start of the negotiating process de Klerk is following, having been the first to meet with Mandela while he was still in jail.

Treurnicht told the crowd that what South African whites wanted was no more than what the Soviet Baltic states of Lithuania and Estonia are seeking or the neighboring black states of Botswana and Swaziland already have -- their own independent state.

The Conservative Party leader rejected de Klerk's proposal for "power-sharing" between whites and blacks, saying: "You either rule or you are ruled. You are either politically free or you are in chains."

"The ANC hates the Boer people and the white nation," he said. They demand our land. They reject our right to exist. But the government still sees its way clear to reach a negotiated consensus agreement with them."

He drew long applause when he said: "Do you think that the move to a black majority rule government is irreversible? It will just have to be stopped."

Announcing that the Afrikaner "third freedom struggle" against oppression had begun, Treurnicht spelled out a 10-point program to defeat de Klerk's National Party "as long as there is a constitutional path open whereby we can regain political control." This would be done, he said, by competing in by-elections, enrolling 1 million voters in the Conservative Party, holding conferences and seeking to "successfully market" the idea of a white state.

Afrikaner nationalists, or Boers as they were earlier known, fought two wars against the British to maintain their own republics, and Treurnicht's reference to the "third freedom struggle" was apparently meant to signal yet another attempt to establish a Boer republic. Afrikaners, descendants of Dutch and French Huguenot settlers, make up about 60 percent of South Africa's 5 million whites.

In the 1989 general election, the National Party won 102 seats in parliament with about 48 percent of the vote, the Conservatives captured 41 seats with 31 percent, and the liberal Democratic Party took 34 seats with 20 percent.

"It is time that we gave serious attention to the acknowledgment and control of our own territory and started to turn it into a definite national possession, a home for our descendants," Treurnicht told the crowd.

Treurnicht said that it was "generally accepted" that such a white state had to be smaller than all of South Africa but said he thought it would be "unwise" to draw its final borders at this stage. His party's highest priority now is to win majority support among whites "for our claim to {our} own land under {our} own government."