The belief is growing here that the South African commando unit that clashed with Angolan troops in that country's northernmost province of Cabinda this week entered Angola through Zaire.

Angola says the commandos, two of whom were killed and one captured late Tuesday, were attempting to sabotage an American Gulf Oil installation in Cabinda, while South Africa says they were seeking intelligence information about guerrilla training bases.

The Johannesburg Star today quoted Angolan sources as saying that a map of Zaire and Zairian money were found on one of the South African soldiers. The newspaper also suggested that survivors of the battle, possibly as many as 10 men, might now be trying to make their way back to South Africa through Zaire.

It speculated that there might be an attempt by the South African Defense Force to rescue them. A statement by the Defense Force later today said that "everything humanly possible is being done to ensure the return to South Africa of those who were involved."

The suggestion that Zaire might have played a supportive role in the infiltration adds a further dimension to the widening diplomatic implications of the South African incursion, which was in violation of a U.S.-brokered disengagement treaty that South Africa and Angola signed in Lusaka, Zambia, in February 1984.

Zaire is ruled by President Mobutu Sese Seko, who has close ties with the United States.

Mobutu is known to be favorably disposed toward Jonas Savimbi's National Union for the Total Independence of Angola rebels, who are waging a guerrilla war with South African support against Angola's Marxist MPLA government. He frequently has allowed foreign journalists to travel from Zaire to see Savimbi, who has his headquarters in remote southeastern Angola.

Zaire, which has territorial claims on the oil-rich Cabinda enclave, also has supported other rebel groups operating against Angolan government forces in the north.

In interviews last fall, Angolan officials expressed fear that even if South Africa withdrew its troops from southern Angola, as it agreed to do under the Lusaka agreement, their country still might face a threat from the north.

This seemed at the time to mean that President Jose Eduardo dos Santos feared UNITA troops might enter his northern provinces through Zaire. Now it appears that South Africans may be doing that, perhaps together with UNITA guerrillas, who have become increasingly active around the capital of Luanda during the past year.

There has been some speculation in South African newspapers since the Cabinda clash that the South African commandos may have been operating with the UNITA guerrillas, as part of a double strategy by the Pretoria government of publicly talking peace with the Angolan government while secretly helping Savimbi's rebels to undermine it.

South Africa today named the two soldiers killed as Louis Pieter van Breda and Ridgard Liebenberg, and the captured commando as Wynand Petrus Johannes du Toit. It did not disclose the men's ranks or units.

In a message to the Luanda government yesterday, South Africa asked for an urgent meeting to discuss the return of the captured commando, who is in a Luanda hospital, and the bodies of the other two.

Angola rejected Pretoria's request Saturday and instead demanded an explanation, The Associated Press reported from Luanda.

"The Angolan government has no intention of discussing this question with the South Africans within the next few days," said Raimundo Sottomayor, head of the official news agency Angop.

Sottomayor, at a meeting with foreign reporters, said he was told by high-level Angolan officials that Angola has not been officially notified of South Africa's request. He quoted the officials, whom he did not identify, as saying Angola "demands an explanation from South Africa for this criminal act."