President Pieter W. Botha warned today that South Africa's raids Monday on what it said were African National Congress guerrilla bases in neighboring black countries were only a "first installment" in a campaign to crush the outlawed black nationalist movement.

In his second hard-line speech to Parliament since the raids, Botha told foreign critics who have raised a storm of protest over the attacks that "we will not be deterred by fanciful arguments that are being advanced here and abroad."

"South Africa has the capacity and the will to break the ANC," he declared.

Botha made his defiant speech amid stirrings of criticism within South Africa that the raids were a military failure carried out at huge cost to the country's economy and international relations.

The attacks into Zambia, Zimbabwe and Botswana reportedly resulted in only two casualties -- a Botswana soccer player and a Namibian refugee -- and damage to buildings.

The editor of the country's leading financial newspaper, Business Day, expressed the sentiments of these critics when he wrote in a personal column today: "Militarily, the gains are piffling or irrelevant. Politically and economically, the cost may well be ruinous."

The government's chief spokesman, Louis Nel, stressed at a press briefing here today that the administration regarded the raids as successful.

"This was a warning shot," Nel said. "We sent them [the ANC] a clear message that we can reach them wherever they are."

Nel said the raids had disrupted the infiltration routes used by ANC guerrillas, which were vital to the insurgent organization. "We are satisfied that the ANC is weaker now than it was before the raids," he added.

In Lusaka, Zambia, ANC President Oliver Tambo urged black South Africans to arm themselves and mount a new campaign to "bring the ruling class to its knees," United Press International reported.

["Let us intensify our armed activities at all levels," Tambo said. "More and more of our people must be armed. Efforts must be redoubled to obtain arms from the enemy and from any other source." Tambo urged participation in a national strike called for June 16. "Let us spread the mood of total civil disobedience," he said.]

Nel also said that while military authorities could not verify exact casualty figures, they were sure more people had been killed than have been admitted by the neighboring black governments.

South Africa has said the raids were carefully planned and precisely executed on the basis of detailed intelligence information.

Neither Nel nor two top security officers who appeared at the briefing were able to confirm or rebut official Zambian and United Nations claims that the target attacked there was a refugee camp run by the U.N. High Commission for Refugees and contained no South Africans.

Pressed on the point, Nel replied: "Until we have seen proof that it is a U.N. camp, we deny it."

An ANC spokesman in Lusaka has said that the organization has facilities in the vicinity of the U.N. camp but that these were not attacked.

Violence continued in black townships throughout South Africa today with another five reported deaths in 23 incidents. The death toll since the current wave of racial violence began 21 months ago is now more than 1,500.

Nel said ANC guerrilla activity had inflicted a total of 78 deaths over the past 10 years.

The huge Crossroads squatter camp outside Cape Town is currently the scene of the bloodiest violence, with 22 people reported killed since Sunday in fighting between conservative and radical black groups for control of the settlement.

More than 80 people have been injured and an estimated 3,000 of the flimsy shacks have been burned. Thousands have fled the shantytown into the surrounding bush and welfare agencies have set up relief stations.

U.S. Ambassador Herman W. Nickel gave $35,000 to the Red Cross today to aid refugees from the fighting. "It is quite obvious that what is happening in Crossroads is a human disaster of major proportions," Nickel said.

In another development, the outspoken editor of an Afrikaans newspaper resigned his job after the paper's progovernment directors reportedly ordered him to change his increasingly liberal editorial policy.

The editor, Harald Pakendorf of Die Vaderland, an afternoon paper in Johannesburg, had urged the government to begin negotiating with the outlawed ANC and told Afrikaners they should adjust to the idea of eventually living under a black government.