South Africa said yesterday that its forces are attacking Namibian guerrillas in a "limited" offensive inside Angola.

The announcement followed a report from the official Angolan news agency (Angop) that South African troops attacked the mining town of Cacinga, 155 miles inside Angola after bombing it intensively.

Although South African troops have staged "hot-pursuit" raids against Southwest African People's Organization (SWAPO) guerrillas in Angola in the past, this was the first time since South Africa invaded Angola during the 1975-76 civil war that this country's Defense Ministry officially has announced such an operation.

The ministry gave no indication of the size of military force that it developed how long it would remain in Angola, or where the offense was being carried out.

Defense Minister Pieter Botha, who released the South African statement, said South African troops entered Angola after large numbers of guerrillas from SWAPO based in Angola repeatedly attacked targets in Namibia, which South Africa governs as the territory of Southwest Africa despite U.N. demands for its withdrawal.

The South African offensive comes at a crucial time in the complex negotiations over independence for Namibia. South Africa, which has been repeatedly condemned at the United Nations for continuing at the United Nations for continuing to control Namibia, just last week accepted a Western plan to lead to independence by the end of the year.

SWAPO, with the support of the Soviet Union, has so far failed to accept the plan. A new round of negotiations is scheduled to he held at the United Nations today involving South Africa and SWAPO, with five Western nations, including the United States, acting as intermediaries.

Western officials have been optimistic that progress could be made at the new talks but the South African attack could deal a blow to those hopes. It would be difficult for SWAPO to show signs of making concessions to South Africa at a time when its forces are under serious attack in Angola.

Botha said: "As a result of the ominous buildup of SWAPO forces in southern Angola and the extensive campaign of intimidation of local inhabitants and the murders of political leaders in Southwest Africa, as well as a large number of border violations during the past few weeks, a limited military operation against SWAPO forces has been carried out over the border."

"The limited operation was embarked on after large numbers of heavily armed SWAPO terrorists recently crossed the border, attacked our forces in Ovambo and fled back to safety in Angola," he added.

Botha said the Ruacana power station on the Namibian-Angola border also was attacked and ex-station on the Namibiane-Angola.

So far this year, 14 South African soldiers have died, and one has been taken prisoner in clashes with the Namibian guerrillas, who have lost 70 of their number since Jan. 1. Twelve civilians have died in this period. South Africa has also accused SWAPO of murdering many civilians, including tribal leaders.