When the going gets tough in Africa, the tough sometimes stage a coup

The occasion was a glittering diplomatic reception at the United States Embassy in a small West African country. Guests arrived either in smart Western business suits or in stately, flowing African robes.

But the decorum of the occasion evaporated soon after the food arrived. African guests seized as much of the food as they could and crammed it into carrier bags to take away with them. Hunger, not greed, was the motiving factor.

''It was the first time that I saw not just poor people, but well-educated professionals - lawyers, businessmen - in such desperate straits,'' an eyewitness to the scene commented afterward.

Hunger in Africa has become so pervasive that it is reaching right across the social spectrum. And the economic crisis facing African countries, mired in debts made worse by falling prices for their agricultural exports, carries with it serious implications for their political stability.

The bloodless coup in Nigeria on New Year's Eve, for instance, was not precipitated by tribal differences. A northerner, Maj. Gen. Mohammed Buhari, seized the political reins from another northerner, President Shehu Shagari, charging that ineptness and corruption had undermined the government and the economy.

But the timing of the coup, within 48 hours of former President Shagari's announcement of an austerity budget, is telling. The severity of the budget was impelled by Nigeria's financial crisis following the slump in world oil prices. Oil revenues account for more than 90 percent of the government's earnings.

As a giant in Africa, Nigeria's latest crisis is likely to reverberate well beyond its immediate borders. Both in population (about 90 million) and oil exports (sixth in selling to the United States), it dwarfs other African nations.

After 1979, when military rule gave way to a civilian democracy, Nigeria not only enhanced its reputation as a leader of black Africa, but also showed it could break out of the entrenched pattern of recurring military rule that has beset so many African countries.

That image has been dented by Nigeria's recent military takeover. At the same time, although the former President was respected for his probity, prominent Nigerian intellectuals at a Boston University African studies seminar only weeks before the takeover were pessimistic about Nigeria. They said a return to the military was becoming increasingly likely.

According to them, corruption had become ''a revolving door'' in which the problem remained unchanged. Only the faces changed.

The new military ruler has an impressive record both as soldier and former oil minister. This is reassuring to Western diplomats that Nigeria's government will remain in able hands for the time being.

But what the recent coup underscores for Africa, as much as for Nigeria itself, is the fragility of political systems when economic pressures become overwhelming.

Thus the year-end announcement of the Nigerian budget - cutting investment spending by 30 percent and imports by 40 percent - was a clear signal to the restless military for remedial action.

Similiar economic and budgetary pressures are weighing heavily on African leaders who feel both their prestige and leadership are at stake.

Africa-watchers share a growing conviction that economic pressures more than anything else will determine the longevity of political regimes. The more severe the economic hardships, the less likelihood there is of political stability.

Only leaders like Kenneth Kaunda of Zambia, who has an impressive popular following at home, are expected to ride out the political storm arising from severe economic problems that require even sterner action to correct them.

All over Africa - in Nigeria, Ghana, Zambia, Zaire, Kenya, Ivory Coast, to name just a few - hard-pressed countries have been forced to turn to the International Monetary Fund (IMF) for financial help. For all these countries seeking IMF rescue operations the price is stiff economic discipline which they don't like. But the alternatives are worse.

Unless they go along with the terms the IMF sets, the economic deterioration is likely to continue. But those terms are liable to spur social and political unrest.

So far some 17 countries in Africa have secured IMF loans. And negotiations or some kind of dialogue with the IMF that could lead to assistance are under way in other countries, such as Tanzania and Nigeria. Before the coup Nigeria was reported to be seeking a $2 billion loan from the IMF to offset an external debt estimated at $14 billion.

The purpose of these IMF loans is to help countries overcome balance-of-payments difficulties and to provide temporary economic relief. But these packages carry with them the assumption that the countries will recover.

The difficulty for countries such as Nigeria with oil or Ghana with cocoa or Zaire with cobalt and copper is that any early economic recovery depends largely on the improvement of commodity prices.

Zaire, for instance, has just concluded a $359.6 million arrangement with the IMF. The IMF said Zaire had experienced ''major problems'' in meeting payments on its external debts because of the drop in its commodity export earnings.

Not all the economic problems of African countries, however, are blamed on world economic cycles. Blame is also attached to economic mismanagement and corruption within the countries.