AFRICA; The People and Politics Of an Emerging Continent. By Sanford J. Ungar. Simon and Schuster. 527 pp. $19.95.

SANFORD UNGAR's exceptionally informative survey of the Africa of the 1980s will become a standard reference, but it is much more. He approaches a difficult subject -- the political, social and economic problems of a generally non-understood continent -- in ways that are entertaining as well as thoughtful. It should be required reading for all would-be Africanists and will be a stimulating review for "old Africa hands."

Best known for his commentary on National Public Radio's All Things Considered, Ungar is also a serious student of Africa. Here he seems to be equal parts philosopher, historian, political-economist and journalist. The mixture works well.

He is obviously fascinated by the continent. But he is a realist, and his reading of Africa's prospects gives little comfort to those who are actively concerned with the drift of African institutions. One feels that Ungar would like to have been more generous than his professionalism would allow. The book could just as well have been subtitled "A Loving Look at Functional Chaos," or perhaps "Facing Disintegration Without Despair."

A major problem is that the book tries to cover too much, with sketches of 31 nations. After an abbreviated history of the "undistinguished" course of U.S. Africa policy through successive Democratic and Republican administrations, in various states of culpable innocence, Ungar wisely focuses our attention on the five countries -- Liberia, Nigeria, Kenya, South Africa and Zimbabwe -- that appropriately receive much attention from U.S. policymakers. Ethiopia could have been included, but was given only a few lines in the brief coverage of Somalia. Perhaps it is just as well, for Ethiopian issues are exceedingly complex and in some ways more Middle Eastern than African.

Inevitably, many African nationalists will find ample occasion to be somewhat chauvinistic when reading about their homelands, particularly in the book's shorter pieces which are grouped into such unflattering categories as "American Clients," "Fallen Stars" and "Desperate Cases." But most will admit that the overall analysis is correct, expecially with respect to everyone else's country.

THE BEST of the book, and the most timely, is the 90-page exposition on the realities of the politics -- specifically including the often misunderstood black politics -- of South Africa. This chapter alone is worth the price of the book, and should be read by anyone remotely connected with trying to find a solution to the problems of that suffering nation. Ungar ends with a terribly poignant and telling quote from a "distinguished elderly Afrikaaner woman journalist," who was asked, "Why can't the most realistic white people just sit down with some widely supported black leaders and agree on an agenda of 12 major problems that the country needs to solve?" She replied wearily: "Because if they solve those 12, then number 13 would be the sharing of power. And that is what we cannot do because that would be like signing our own death warrant."

Elsewhere on the continent, Liberia's head-of-state Samuel Doe will not be pleased with the analysis of the lack of political progress in his country since he overthrew President Tolbert in April 1980. It may be cold comfort that Tolbert and his Americo- Liberian elite receive equally bad reviews. This troubling chapter on "America's stepchild" ends with a few lines that say much. "Doe, like William Tolbert, seemed to have ever less doubt about the true source of his own authority. 'God is the one who chose me to be here,' he (Doe) said flatly in an inteview; 'God knows I ca better help the people.'"

Nigeria, the biggest and most influential nation in black Africa is covered less completely than many would wish, but the broad- brush analysis is informative and generally on target. Ungar summarizes well when he writes of "certain fundamental national problems: corruption in government and business; general economic decline; ethnic tensions; and grave inequities in society." He ends by saying, "For the country in Africa that has, in important respects, come the farthest, there is still far to go."

The section on Kenya is particularly insightful in three areas: on the stress induced by a 4 percent annual population growth in an already overpopulated land where the ideal family consists of eight children; on the wide-open politics within the Kenyan "single- party" system and on the dangers of overloading our democratic African friends with an excessive American presence.

Ungar's treatment of Zimbabwe, while fair and balanced, seems to take on the tone of the jilted lover. In fact, most Western observers expected too much from Mugabe. Conservatives expected a radical red monster. Liberals wanted a brilliant and efficient saint. Both were disappointed. We've got Mugabe, a living, breathing, dedicated African nationalist with a full complement of warts. And, after all, when compared to his neighbors, north and south, he's not doing too badly.

All things considered, Ungar has given us a first-rate guide to the political, economic and social realities of Africa. For those who are about to embark on any sort of journey into those turbulent climes, a word of advice: don't leave home without it.