HENRY KYEMBA, the next-to-last civilian minister in the Amin cabinet in Uganda, defected in May 1977. In this brief, instant book which the author intends to present as testimony before the United Nations opening session on September 20, Kyemba reveals the chilling anatomy of the Idi Amin years.

He was remarkably well placed to undertake this task. Ever since independence in 1962, Kyemba has worked in the inner sanctum of power. He finished his university training just in time for independence, and moved at once onto the personal staff of former Prime Minister (later President) Milton Obote. By the time of the Amin coup in 1971, Kyemba had become principal private secretary to Obote. With a disconcerting agility, he was able to retain these functions under Amin, then became minister of health in 1972, where he remained until his defection. During much of this period, he was on intimate terms with Amin.

What then does this witness add to the macabre study of Aminology? Kyemba's book mainly reinforces the evidence of a tale whose main outlines are already well known. He provides certain details which clarify events that led to Amin's seizure of power in 1971, and illuminates the bizarre processes by which the regime carries out its daily business. New bits and pieces are added to our understanding of particular episodes, such as Amin's connections with the Zaire rebels in 1965, the September 1972 invasion by Ugandan exile units, the Israeli raid on Entebbe, and the Makerere University confrontation in 1976.

Those with the curiosity and the stomach to seek documentation on Idi Amin Dada's sanguinary tyranny can read accounts by academician Ali Mazrui, London Observer correspondant David Martin, and the newly published report of the International Commission of Jurists. Kyemba substantially confirms these earlier contributions.

What manner of man is Amin: too illiterate, Kyemba affirms, to ever be known to communicate in writing to anyone, yet crafty enough to out-maneuver and embarrass no less a politician than James E. Carter on the human rights issue? How can a man who has singlemindedly destroyed the economy of his country, killed - by Kyemba's estimate - 150,000 of his citizens, remain in power, and shrewdly foil so many conspiracies against his rule? At leasts 20,000 of the most educated Ugandans have fled his reign of terror. How can the country survive at all?

Kyemba does provide us many insights into this questions. The persistent rumors that Amin's behavior derives from a syphilitic condition are persuasively spiked. Far from a debilitated man, Amin has extraordinary energies, physical and sexual. He has crafted an apparatus of terror - antecedents of which date from the Obote period - of multiple security agencies. Their inner corps is composed of persons who, like Amin, come from Kakua, Nubian and Muslim backgrounds, augmented by southern Sudanese imports: all are socially marginal, and politically vulnerable if anythings should happen to the Amin system. Their loyalty is maintained by high rewards, and license to extort.

The career of Henry Kyemba helps us to understand another aspect of Uganda's survival. Although many members of the elite have defected, other remain; Kyemba continued to serve as minister for five years after he first became aware of the murderous nature of the regime in 1972. Indeed, he candidly states that the only left when there were unmistakable signals that his name was up for elimination. Uganda is endowed with one of Africa's most abundant educated class, and was equipped with and excellent civil service. Many talented Ugandans still try through improvisation and baling wire to hold the state together. Indeed, the very fact of defections has opened to many younger administrators promotions that would have been years away through normal processes. And for many, flight is simply not a feasible alternative: doctors and academicians have internationally transferable credentials, but administrators are unlikely easily to find employment in neighboring countries, much less in Europe. Relatives of exiles are potential victims of regime vengeance; those tempted by conspiracy must reckon with likely retaliation visited upon their entire community in the event of failure.

Kyemba concludes that only international action can bring an end to the agony of Uganda. If he is right, this is a depressing conclusion, as anything exceeding moral reprobation is unlikely. More depressing is the contemplation of what might follow even a successful internal conspiracy. Not only would Amin need to be removed, but the brutal and sinister entourage of senior army officers and agents of the state security bureau would have to be dispersed, Kyemba shows that Amin seized power in 1971 partly in self- defense, as he knew that Obote wished to eliminate him. So would Amin's henchmen have to seek power as the only means of self-protection from the furies of the populance. They have the guns, the planes, the tanks. Prospects for deliverance, in the these circumstances, are problematic.