Angolans begin to ask just what Cuban soldiers are doing for them

When the South African Army invaded Angola last August, Cuban troops kept carefully in the background. The Angolan authorities explained at the time that they wanted to avoid internationalizing the conflict and that, anyway, the Cubans were needed elsewhere in the country.

A month ago, Angola's only oil refinery - on the outskirts of Luanda - was blown up. It was not up to the Cubans to guard it, but the attack certainly had Angolans asking:

''If the Cubans are not here to fight the South Africans, and if they do not protect our most vital installations, what exactly are they here for?''

It seems to be a relevant question, especially as the thousands of Cuban soldiers and civilian advisers in Angola are charging hundreds of millions of dollars a year for staying on.

It is true that it was only thanks to an air bridge of Cuban troops and Soviet arms that the Popular Movement for the Liberation of Angola (MPLA) ever gained power when the Portuguese left in 1975. It is also true that it was only thanks to the Cubans that a coup attempt by a black power radical faction of the MPLA failed in May 1977.

But with the Cuban soldiers showing an increasing reluctance to get involved in any outright military actions, more and more questions are being asked about their role.

Are they a kind of Praetorian Guard that provides the Angolan leadership with its only reliable protection? Or are they the jailers who keep that leadership locked in the cage of Kremlin orthodoxy?

President Jose Eduardo dos Santos of Angola says the Cubans and the Soviet military advisers are needed to transform Angolans who learned to fight in a guerrilla war into the soldiers of a modern army.

The combined efforts of Cubans and Angolans have clearly failed in their mission of pacifying the country. The Angolans admit that they have lost control of a large part of their southern border with Namibia to the South Africans. What they do not admit so publicly is how much of the rest of the country they have lost to opposition guerrilla groups.

The National Union for the Total Independence of Angola (UNITA), whose leader , Dr. Jonas Savimbi, was received by US Secretary of State Alexander M. Haig Jr. earlier this month, keeps much of the center and southeast of the country in a permanent state of chaos.

The long-dormant National Front for the Liberation of Angola, which used to operate out of Zaire, is showing signs of life again in the north following a shakeup in its leadership.

But most worrying of all, because of the economic implications, the Front for the Liberation of the Enclave of Cabinda is reported to be increasingly active in Angola's main oil-producing province, although Gulf Oil's operations have not been affected so far.

All this means that the coffee plantations of the north are not producing; the timber in the forests of Cabinda is not being felled; and the Benguela railway that used to carry copper from Zaire and Zambia to the Atlantic port of Lobito is the constant target of sabotage.

In addition, farmers are no longer planting maize (corn) along the railway corridor. That means that Angola has to import its staple food. But the country has less and less money to spend on imports, partly because oil prices and production have dropped, partly because so many diamonds are being smuggled that what used to be Angola's other big export will only make a tiny profit this year , if that.

Meanwhile, the guerrilla war goes on and the South Africans stage deeper and more humiliating raids. The cost of buying arms goes up and there is less to spend on the people. And, after six years of independence, discontent rises. Even the most idealistic stop believing in the revolution.

Money could solve many things, but none is forthcoming from Angola's allies in the Soviet bloc, who have too many problems of their own.

Thus Angola has only one way to turn. It must look to the West for either money or the political solutions that could end the guerrilla war and allow the economy to recover.

This is one reason the Angolans have pinned so many hopes on the efforts of the Western ''contact group'' - the United States, Canada, Britain, France, and West Germany - to solve the problem of Namibia. But it is not just the independence of its southern neighbor that Angola is after.

More and more, Angolan officials speak of the need for a Namibian settlement that would guarantee Angola's security in the south, in other words, a settlement that would end the civil war with UNITA.

Against this background Angola's leaders, having run out of ways of solving the country's military, economic, and social problems, are seeking talks with the Reagan administration - although they know US recognition of their regime will come only after the Cuban troops have gone.

It now looks as though the Angolans are at least prepared to discuss a Cuban withdrawal. But will the Cubans be willing to go? And even if they are, what will happen to the regime once they have gone?

There is a large Cuban barracks just outside President Dos Santo's palace in Luanda. The entrance to Huambo, Dr. Savimbi's former headquarters, is guarded by a Cuban barracks. Who will protect President Dos Santos in Luanda or the MPLA in Huambo once those Cubans have gone?