Senior envoys from Angola, Cuba and South Africa, concluding four days of U.S.-mediated negotiations, announced agreement Friday on an unspecified "sequence of steps to achieve peace" in southern Africa.

The negotiators, in a joint communique, said the substance of the agreement would be revealed only next Monday after final approval by their governments in Luanda, Havana and Pretoria.Following that, more peace talks mediated by Chester A. Crocker, the U.S. assistant secretary of state for Africa, will be held during the week of Aug. 22 at a site to be determined, they added.

The communique appeared designed as a lowest common denominator of agreement to convey an impression of accomplishment at the end of this round of talks. This was seen as an important goal for Crocker after an angry Angolan and Cuban outcry Wednesday over South Africa's disclosure of its negotiating position in violation of a confidentiality accord.

(In Washington, U.S. officials said the Geneva announcement was intended as a signal that the negotiations are making what one official called "rapid and significant progress" toward resolving many of the obstacles impeding an agreement, Washington Post staff writer John M. Goshko reported.

(They said the progress has been so good that the negotiators decided that their tentative agreements should be referred back to their respective governments for approval and instructions on what to do next.)

Although it spoke of agreement on "a sequence of steps," the communique gave no indication whether those steps involved movement on the ground to resolve the bloody conflict or only gestures connected with further talks on the longstanding dispute.

Foreign Minister Roelof F. "Pik" Botha of South Africa, who also announced the agreement in Pretoria Friday, described it in less concrete language than the communique here. He said the accord covered only "steps considered necessary to further the search for peace in southwestern Africa," indicating that what was agreed would not solve the conflict itself but instead would facilitate further negotiations.

In that context, press reports in South Africa, quoting diplomatic sources there, said a provisional cease-fire in Angola could be announced for next week. This would improve the atmosphere for what the reports suggested are likely to be more protracted negotiations over the future of Cuban troops in Angola and South African control in the territory of South-West Africa, or Namibia.

The foreign minister said President Pieter W. Botha will consult Monday with Louis Pienaar, the administrator of Namibia, and then inform Cuba, Angola and the United States whether South Africa formally accepts the agreement reached here. It was unclear what the consultations would cover since Pienaar is appointed by the South African government, which has administered the territory since World War I.

Officials from all four countries involved in the negotiations here declined to comment on the talks or explain their ambiguous communique. A senior South African official noted earlier, however, that the government in Pretoria faced right-wing opposition to its willingness to accept a cease-fire and agree, even in principle, to eventual withdrawal from Namibia.

The thorniest issue confronting Crocker as he shepherds the parties through the negotiations revolves around synchronization of Cuban troop withdrawal from Angola and South African departure from Namibia.