The photograph of the author on the back of the dust jacket--a black dust jacket, with the title in shrieking white, "Salvador"--shows a wraith-like woman wearing enormous sunglasses and looking away, as though the world causes her to avert her gaze.

Joan Didion has written haunting novels and essays about marginal, disaffected people. Last June she spent two weeks in a country that she (or Joseph Conrad or Graham Greene) could have dreamt up for a novel about life in extreme situations. The result is a book that shows how hard it is going to be to do what we must do: think about El Salvador.

El Salvador's history is, she says, with nice understatement, "resistant to heroic interpretation." There is no revered liberator, and public statues tend toward representation of abstractions, such as Winged Liberty of the spirit of revolution. It is, she says, a history "devoid of shared public purpose or unifying event, a record of insensate ambitions and their accidental consequences."

The texture of life, with its endemic apprehension, is suggested by this fact: The word "desaparecer" (disappear) is in Spanish both transitive and intransitive, and persons speaking English in El Salvador are apt to say "Jones was disappeared at the hotel" or "the government disappeared the students." There is, Didion says, a local vocation for violence.

Some priests and nuns in the countryside tell Didion there are fewer bodies around since the spring elections. But then they begin reminding each other of various bodies, and the toll mounts. "They spoke of these bodies in the matter-of-fact way that they might have spoken, in another kind of parish, of confirmation candidates, or cases of croup." But things could be worse. They have been.

General Martinez, dictator between 1931 and 1944, conducted a cautionary massacre in 1932, killing between 6,000 and 30,000. (A scholar says of Salvadorans, "Statistics are not their strong point.") Reading a U.S. government "Area Handbook for El Salvador," prepared to give U.S. personnel what the government considers "basic facts," Didion found these thought-provoking sentences about Martinez:

"He kept bottles of colored water that he dispensed as cures for almost any disease, including cancer and heart trouble, and relied on complex magical formulas for the solution of national problems. During an epidemic of smallpox in the capital, he attempted to halt its spread by stringing the city with a web of colored lights." In a radio chat with his countrymen, he revealed: "It is good that children go barefoot. That way they can better receive the beneficial effluvia of the earth. Plants and animals don't use shoes."

His grandson told Didion: "It was sometimes strange"--sometimes?--"going to school with boys whose fathers my grandfather had ordered shot." But, he added, "When you've read Schopenhauer, Nietzche, what's happened here, what's happening here, well. . . ."

Well. Perhaps we should make Nietzche's "Beyond Good and Evil" the new "Area Handbook for El Salvador." But what else is to be done for (with? to? about? Choosing the right preposition is a problem) that country that would fit with room to spare in one-half of California's San Bernardino County?

Much of Didion's book appeared in the New York Review of Books, a forum suitable for Didion's laconic conclusion that no one could be "unequivocally convinced that American interests lay on one side or another." But the book is a report of an exotic sensibility's reaction to a shocking place; it is not a policy paper.

It will, I suspect, arouse in the normal reader an understandable impulse to avert one's gaze. The book comes from Didion as an almost aesthetic judgment. But such aesthetic judgments become political acts. This genre of writing--a hybrid of journalism and literature; call it literary impressionism--derives its force from its preoccupation with extremes (not even El Salvador is all extremes).

But such writing is a useful impediment to a certain kind of cheerfulness. Our amiable democracy is in constant danger of auto-intoxication as a result of the reiteration of phrases about "nation-building" and "nascent democracy." Delirium is encouraged by the required certification of El Salvador's human-rights progress every six months so that other American aims can be pursued.

But books such as Didion's--a reaction of revulsion, visceral yet controlled, in response to savagery on all sides--can weaken the tenuous hold Americans have on this truth: there are national needs-- such as the need to prevent the multiplication of Cubas--that are important regardless of the nature of the company we must keep when pursuing them. Fastidiousness is a virtue in literature and an impossibility in politics.