Describing in detail for the first time how it sees the black unrest sweeping South Africa, the Botha administration said today the trouble was the result of a Soviet-directed campaign to destroy the government's initiatives toward peaceful reform.

Black radicals who were puppets of Moscow were trying to prevent the emergence of a moderate black leadership that was willing to negotiate a new constitutional deal with the government, Deputy Foreign Minister D. J. Louis Nel told foreign correspondents and diplomats at a briefing in Pretoria.

Nel, the government's official spokesman, said the aim of the communist-backed radicals was to make South Africa ungovernable as a first stage in bringing about a socialist revolution.

He referred to President Pieter W. Botha's statement yesterday that the president had ordered "appropriate steps" to end the unrest, but he refused to answer questions on what these steps were. "I don't think it would be wise to give details about the government's strategy because it could lead to certain reactions to prevent it from succeeding," was all Nel would say.

Botha's statement before a specially summoned joint session of the country's tricameral Parliament has led to widespread speculation that a major crackdown on antiapartheid activists is imminent, but by late tonight the security police still had made no move.

Speaking against a backdrop of continuing unrest in a number of segregated black townships in which four more people died today, Nel described a scene not of racial conflict between black and white but of black civil war, with black radicals seeking to eliminate black moderates.

The radicals were killing and intimidating the moderates, Nel said, compelling the police to intervene. This police action was all that appeared on foreign television screens, he complained.

Arguing that his government was committed to expanding democratic institutions for blacks, Nel said it had established 32 local government councils for blacks since 1977 and was transferring administrative powers to these councils.

The "moderate blacks" serving on these councils were willing to negotiate with the government for the constitutional advancement of their people, and this was why they had become targets of the black radicals who saw them as a threat to the revolutionary objectives.

Since last September four black councillors had been killed and 109 assaulted. Another 147 had been intimidated into resigning. In addition four black policemen had been killed and 54 injured in the township unrest, Nel said.

Within hours of Nel's briefing, it was announced that another four councillors had resigned in Kirkwood township in troubled eastern Cape Province.

A common explanation heard in the black townships is that the councillors and policemen are targets for mob attacks because they are seen as collaborators in the system of apartheid, as the policy of ethnic compartmentalization is called. A "system black" is the pejorative term used for anyone holding office in the administrative structure.

Nel brushed aside suggestions that they were being attacked because they were seen as quislings, however, insisting that it was because they were moderates who posed a threat to the aims of the radicals.

"It has become clear that the strategy of the rioters and the people inciting the riots is to destroy any potentially successful democratic structure," Nel said.