JOHANNESBURG, JULY 25 -- African National Congress leader Nelson Mandela today denied that there is a Communist revolt within his organization against peaceful negotiations with the South African government.

He described police allegations that there was such opposition as "totally unfounded."

"Members of the National Executive Committee of the ANC as well as the entire membership is unanimous on the question of working with the government to bring about a democratic transformation of this country," Mandela said. "The method we have selected is that of peaceful negotiations between the ANC and the government."

Mandela's comments came a day after the South African Foreign Ministry called in the diplomatic corps to discuss the recent discovery by police of arms caches and computer files allegedly found in the homes of members affiliated with both the ANC's military wing, Spear of the Nation, and the South African Communist Party.

The African nationalists and Communist Party historically have been close allies and many Spear of the Nation officials and National Executive Committee members are also members of the party.

Foreign Minister Roelof F. Botha read the ambassadors some of the information allegedly found on one computer disk, which detailed Communist Party plans to continue preparations for armed insurrection in the event negotiations with the government falter, according to Western diplomatic sources.

The computer disks also allegedly contained the names of Communist Party members in the Spear of the Nation who are involved in plans for an uprising, according to these sources.

Botha was questioned extensively by a number of ambassadors about the validity of government evidence and how it points to a separate Communist plot for an armed insurrection, the sources said.

The issue is complicated by the fact that the ANC is still committed to armed struggle and infiltrating guerrillas and weapons into the country. Mandela defended comments made by his military chief of staff, Chris Hani, who threatened last week to "seize power" by force if peace talks fail.

"What Chris Hani said was that if the government pulls out of the negotiations then we will be forced to continue with the armed struggle," Mandela said. "Everybody knows that we are conducting an armed struggle in this country."

The police reportedly have arrested 10 people in connection with the alleged Communist insurrection plot. Since April, security forces have apprehended about 40 Spear of the Nation members.

The South African government and the ANC have gone out of their way in the past few days to reassure the international community that they intend to continue with the peace talks and hold to their scheduled meeting Aug. 6. The delegates are expected then to announce a joint agreement for the release of all political prisoners and return of political exiles -- the two main obstacles delaying the start of formal constitutional talks on ending apartheid and granting political rights to the black majority.

The ANC's National Executive Committee issued a statement today after a two-day meeting reaffirming its commitment to move forward "as speedily as possible" toward a settlement with the government.

Mandela said he had told President Frederik W. de Klerk that it had not been easy for the ANC to contact all the Spear of the Nation guerrillas infiltrated before the May 4 agreement with the government, which committed the African nationalists to a peaceful process of negotiations.

Mandela said some guerrillas were still operating under "old instructions" and seemed to suggest this might be why police were still discovering stockpiles of arms.

"It is not easy for an organization which has been operating as an illegal organization to take decisions and make sure that those decisions reach every member who is affected," Mandela said. "I asked Mr. de Klerk to give us time in this regard."