JOHANNESBURG -- Government evidence that the African National Congress and Communist Party are engaged in a secret military buildup while negotiating with the government on the nation's future has served to highlight how difficult the road to a "new South Africa" is likely to be.

The buildup, which the ANC and Communists have confirmed, raises fundamental questions about whether the negotiating process can proceed in South Africa if these two closely allied organizations continue to prepare for armed struggle and the government continues to arrest their leaders.

The government and the ANC have begun preliminary talks aimed at bringing about formal constitutional negotiations on ending South Africa's system of apartheid, or racial separation, and giving political rights to the 30 million blacks who constitute the vast majority of the nation's population. But there are still no agreed-upon rules of conduct in the unprecedented negotiating process, and unanswered questions abound.

For example, can the government of President Frederik W. de Klerk be expected to grant immunity to ANC negotiators if they are simultaneously engaged in clandestine military preparations? And how does the government deal with the ANC-Communist Party alliance in which commitments undertaken by the ANC may not be binding on the Communists?

On the other hand, why should the ANC and Communist Party lay down arms and formally end their commitment to the armed struggle before they have any tangible results from a negotiating process that has not even really begun? What concrete assurances do they have at this point that de Klerk will keep his promises of ending apartheid and white majority rule?

These are the conflicting questions facing both de Klerk's government and the ANC in what William Zartman, head of the Johns Hopkins University School of Advanced International Studies' Africa program, called a unique case in the annals of the transfer of power from whites to black majorities.

"It's a case where the white colonists are not going to leave and may even become partners in the new government," he said.

He was referring to the 4.5 million whites here, 3 million of them Afrikaners, or descendants of Dutch, German and French Protestant settlers who came here in the 17th century. Unlike the British, French and Portuguese who gave up African colonies, today's Afrikaners have no European homeland to which to flee.

Zartman also said he could think of no other example of negotiations taking place inside an African country between a white minority government and black nationalist leaders who were also conducting a guerrilla war. Usually talks took place in a European city or a neutral African capital.

The world has recognized South Africa as an independent state for 80 years, and neither the de Klerk government nor the ANC has suggested that negotiations should take place outside the country or under the mediation of an outside power.

But central -- and also unique -- to the South African situation is the decision of the ANC-Communist alliance to embark upon a military buildup.

Communist Party and ANC leaders have publicly stated here that their organizations are indeed strengthening their underground and slipping arms and guerrillas into the country. They argue that there has been no agreement yet to suspend hostilities and that even with such an agreement they have no intention of formally renouncing their commitment to "armed struggle" in the absence of a final settlement. Therefore, they argue, continued military preparations must be accepted as parallel to negotiations.

This fight-and-talk strategy is typical of other African independence movements of the past four decades. But in South Africa's situation, Zartman said in an interview here, this military push "puts a lot of pressure on the negotiating proceess. You don't bring in tons of arms if you expect negotiations to succeed, and it's prima facie evidence you don't expect them to succeed."

Yet another problem, namely how to build mutual trust between the two negotiating partners, became clear last week with the close ANC-Communist Party alliance at the center of controversy within the de Klerk government.

The government alleged that the Communist Party was involved in a secret meeting outside Durban May 19 in which some of its leaders said an eventual cease-fire agreement or "suspension of hostilites" would not necessarily be binding on the party.

According to government leaks to the local press last week, Communist Party officials said at a secret meeting in May at Tongaat, outside Durban, that the party would not be signatory to any cease-fire agreement and therefore would not be bound by it.

One speaker is reported to have said: "While the cease-fire happens nationally, the people on the ground have to continue to be on the attack and eliminate warlords and the councilors" of South Africa's black townships. This was an apparent reference to the fighting underway in the Natal between ANC supporters and the "warlords" of an opposing faction, Inkatha, led by Chief Mangosuthu Buthelezi.

One of the Communist leaders was allegedly the party's secretary general, Joe Slovo, who is emerging as a top ANC negotiator and is part of the five-man ANC delegation scheduled to hold a second round of talks Aug. 6 with the government. He also participated in a round of talks in early May in which the two sides committed themselves to "a peaceful process of negotiations."

Slovo categorically denied at a rally Sunday that he was at the alleged secret meeting or ever said that his party did not consider itself bound by any ANC-government agreements. He also formally committed the Communist Party to the early May ANC-government accord.

The government has told the diplomatic corps -- and leaked to the local press -- that its information about Communist plans was taken from a computer disk seized in one of the Communist Party's "safe houses" in Natal.

De Klerk was reportedly particularly upset because the alleged meeting was held after the ANC agreed in May during talks with the government in Cape Town to work to end the existing climate of violence and to foster "a peaceful process of negotiations."

Both ANC and Communist Party leaders have heatedly denied the existence of a "Red plot" or any detailed plan to launch an armed insurrection. But they have confirmed that they are continuing, even accelerating, a military buildup, calling it an "insurance policy" in case negotiations do break down and they feel obliged to resume hostilies.

The government campaign against the Communist Party -- and Slovo in particular -- has placed ANC leader Nelson Mandela in a delicate spot. He is unlikely to repudiate the ANC's alliance with the Communist Party under government pressure; rather, he has rushed to reaffirm it. Furthermore, so many top ANC officials are also Communist Party members that to remove them from the negotiating team would seriously weaken the ANC's position.