South Africans are cautiously hoping that the American-approved intervention of French and Belgian troops in Zaire last week will lead to a more active western role in confronting Soviet and Cuban-backed operations in Africa an effort they have repeatedly urgued on the West.

The Western intervention "is good news" and could be "the beginning of a new era on the continent," read an editorial in the Afrikaans paper, Die Vaderland. Another progovernment paper wrote that the Western reaction "indicates that they fear the domino principle in Africa."

Government officials, however, were more circumspect.

"We are just watching to see what it means," a Foreign Ministry spokesman said. "I think you need to distinguish between what people would like to happen and what might happen. In this part of the world we have grown cynical and gotten round to the idea that nothing is going to make the West do anything about Soviet penetration."

Anxiety about Soviet activity on the African continent is the tiller of foreign policy in South Africa, where it is firmly believed that Moscow's foreign strategists concentrate on planning how to "cripple the West" by cutting off its African-supplied minerals. This is why the Soviet Union wants to topple white rule in South Africa, which controls most important mineral resources, government spokesman say.

The rebel invasion of Zaire from neighboring Angola therefore was watched closely here because, for the South African government, "it was yet another example of Communist agression," said David Willers, assistant director of the independent South African Institute of International Affairs.

Any Soviet-backed threat to President Mobutu Sese Seko of Zaire "revives the specter of a red link across Africa." said a Foreign Ministry official, because Zaire borders on Angola and Mozambique, both ruled by Marxist-oriented governments.

The Katangan invaders setout from camps in Angola and were equipped with Soviet weapons. Cuba has denied that any of its 20,000 troops stationed in Angola had anything to do with the operation.

Before French paratroopers were dropped on the mining town of Kolwezi last week to rescue white families trapped there by there rebel forces. Prime Minister John Vorster publicly advocated Western intervention.

The South African press and government have followed intently the opposing tugs at President Carter's sleeves by U.S. Ambassador to the United Nations Andrew Young and by national security adviser Zbigniew Brzezinski. Young favors a cool stance toward Cuban and Soviet involvement, saying that in the long run, African states will tire of the Soviet relationship and turn to the West for help with their economic advancement. Brzezinski wants to counteract Soviet and Cuban moves actively, supporting pro-Western groups.

South Africa's interest in the Zairian crisis also revolves around the fact that the huge central African country is an important ally.

But because most of black Africa condemns Pretoria for its domestic racial policies, this relationship is veiled.

Zaire quietly imports a vast amount of manufactured goods - and according to one trading organization's estimate, 50 percent of its food - from South Africa.

Zaire also acts as a "staging post through which South African contacts can be channeled to other blalck African countries," Millers noted. In the past, South Africa and Zaire have cooperated on major issues. South Africa said its intervention in the Angolan war against the Cuban-backed Popular Movement for the Liberation of Angola was approved by several black African countries. Zaire, which was supporting its own faction in Angola was one of those countries.

Last year, when rebels tried unsuccessfully to take Kolwezi, South Africa rushed extra supplies to Mobutu and reportedly also lent him some military advisers.

Facing problems of its own in Namibia (Southwest Africa), where Cuban backed guerrillas are operating. Pretoria no doubt takes solace in the lowered threshold of tolerance for any future Cuban-supported action in Africa.

Because of the danger to whites in Kolwezi, the West was forced into action and now the French-speaking countries of Africa are pressing for a stonger U.S. role in countering Cuban-Soviet activities - all of which is good news for South Africa.