Delegations from South Africa and Angola met for cease-fire talks today amid speculation that prospects for agreement have deteriorated because of reports that anti-South African guerrillas have infiltrated a large group of insurgents into Namibia.

In an obvious reference to the infiltration Sunday, Foreign Minister Pik Botha said "recent events" had greatly diminished the prospects of a truce.

Last week South African officials were privately expressing confidence that a cease-fire deal would be signed and said hostilities in the 16-year bush war along the Angolan-Namibian border had been scaled down to the point of a de facto cease-fire in anticipation of this.

The optimism evaporated during the weekend with news that the South-West Africa People's Organization (SWAPO), which South Africa is fighting in the war, had infiltrated a large group of insurgents into Namibia, also known as South-West Africa.

Defense headquarters in Pretoria said today that 129 of the insurgents and two South African policemen had been killed in numerous exchanges.

A South African delegation that met with Angolan officials in December on the Cape Verde Islands was headed by Botha. The delegation for today's meeting--also on the Cape Verde island Ilha do Sal--is made up of lower-level officials, led by Johannes van Dalsen, director-general of the Department of Foreign Affairs. With him is the ambassador to Washington, Brand Fourie, and the former ambassador to the United Nations, Riaan Eksteen.

According to news agency reports from Ilha do Sal, the Angolan delegation is led by Interior Minister Alexandre Rodrigues and includes Deputy Foreign Minister Venancio de Moura and top Defense Ministry and military figures.

According to western diplomats here who are acting as mediators in the drawn-out Namibian negotiations, South Africa regards the infiltration of the insurgents as a breach of trust, contending that SWAPO took advantage of the deescalation to step up its activities. South Africa sees this as a sign that SWAPO might also take advantage of a cease-fire, the diplomats said.

Five western nations--the United States, France, Canada, Britain and West Germany--have been trying to reach a settlement to end South Africa's occupation of Angola.

Three weeks ago Botha told foreign reporters here that he believed the purpose of a cease-fire was to help build trust between the two sides.

"We don't trust each other now. It may help to have a period during which we can prove to each other that we are serious," Botha said.

South Africa first proposed the cease-fire at the meeting on Ilha do Sal last Dec. 7. That was the first official meeting between the two countries, although there had been several secret meetings before that.

Both Botha and South African Defense Minister Magnus Malan were in the first delegation that went to the island, together with the deputy minister of information, Barend du Plessis.

According to diplomatic sources here, the proposal that South Africa put forward was for a two-stage cease-fire.

The first stage would be simply to stop hostilities with all forces remaining in place, which would mean South African troops, who have been in more or less continuous occupation of large areas of southern Angola, would remain there.

After two months the second stage would begin, with the South African troops withdrawing to the Namibian border, and Angolan troops, with Cuban troops who are supporting them, to a line about 175 miles north of the border. The SWAPO guerrillas would have to withdraw to a second line farther north.

After the Angolans had pondered the South African proposal for more than a month, the U.S. ambassador in Zambia, Nicholas Platt, flew to Luanda to urge them to reply. According to sources here, he received an encouraging response.

This led to the setting up of today's meeting, amid growing speculation that agreement was imminent.