THE WAR which broke out in Spain in July 1936 and ended in March 1939 was not only a fratricidal struggle between Spaniards, it was also an international rehearsal for World War II. An Italian Army Corps under General Roatta and the Nazi Condor Legion on the Franco side tested the weapons and the tactics of the Axis against the Russian fighter planes and tanks of the Republic as well as against the left-wing volunteers from all over Europe and America who served in the International Brigades. It is from these foreign sources that the outside world has formed its impressions of the war: from the first hand accounts by returning (Esmond Romilly's Boadilla and George Orwell's Homage to Catalonia (for example) and from the images created by the poets (especially Auden - in "Spain, 1936," a poem he later excluded from his collected work) and the novelists (Hemingway and Malraux above all).

The Spaniards, who did most of the fighting and suffering, have, except for the defeated exles, written little; after Franco's victory in 1939 a silence fell on Spain."The civil war," says one of the speakers quotes in this remarkable book "was never discussed in my family. My father's brother was shot by the Franquistas; my mother's father . . . was shot by the reds. My father had a lot of medals which, on his death, we found; but he never told me on what fronts he had fought or any of his experiences. All I knew about his war is what I learned for myself. At home there was complete silence."

For nearly 40 years no Spanish voice was raised to talk about the war except the strident official voice of the regime. In this book the silence is broken; people who held their tongues in fear for decades here pour out their memories, their sorrows and hatreds, their judgments, fruit of long solitary meditation, on what went wrong.

Blood of Spain is an "oral history": an "intelligible 'mosaic' of more than 300 personal accounts" from interviews . . . recorded in the twilight of the Franquista era, between June 1973 and May 1975." The book is an attempt "to describe the major contours of the war through eyewitness narration," and it achieves a remarkable objectivity. "Personal accounts were deliberately sought in five regions: two on the republican side" (Madrid and Barcelona with their adjacent countryside), "two on the nationalist side" (the Seville-Cordoba area and the territory from Salamanca to Pamplona) and one area, the North, which began under the republic and was captured by the nationalists halfway through the war. Fraser has drawn on the enormous amount of material he recorded (2,750,000 words - of which he has used less than 10 percent) to produce a series of unforgettable pictures of the war at every stage of its long drawn-out agony.

For each period an opening section, utilizing details from the reminiscenes of many different contributors and also brilliantly chosen quotations from contemporary newspapers and public speeches, sketches the main events and their political background - the rising, first combats, the defense of Madrid. This is followed by sustained individual accounts, entitled "Militancies" and "Episodes" which, mostly in the participants' own words, recreate the action and suffering of typical men and women on both sides - a Falangist farmer, a anarchist textile worker, a Carlist peasant, a Socialist railwayman, a Madrid priest.

These accounts are in many cases passionately concerned with politics; indeed the author concedes that the book may seem "overly political." But this emphasis was unavoidable; the dictum that war is the continuation of politics by other means is doubly true of civil war. Fraser's book is "based on the conviction that the civil war was won as much in the rearguard as at the front" and that it was in the rear that "the social and political issues at stake had their clearest expression." These issues, prominent among them the crucial question facing the republicans, whether to make the revolution now (the anarchist position) or to win the war first (the communist strategy), are discussed from different angles as the voices Fraser has recorded probe the action of those three violent years for a fuller understanding.

The reader not familiar with the politics of what Gerald Brenan aptly called the Spanish labyrinth may at times find it hard to believe that so small a country had so many parties and even harder to remember the political identities of the CNT, POUM, UGT, ANV, CEDA and many another acronyms, but he should not lose heart - this is a book which deserves and rewards careful reading

In any case, the politics never become abstract; they were quite literally a matter of life and death for thoseconcerned. And in the many grim accounts of death, escaped by a hair'sbreadth or faced with legendary Spanish courage, of heroic self-sarifice and cold-blooded massacre, of unpredictable gestures of kindness and equally unpredictable acts of cruelty, Blood of Spain recreates the peculiar horror of war waged between brother and brother, father and son- that calamity from which a Roman poet, Lucan, born at Cordoba, prayedfor release so many centuries ago: "Make us enemies of the whole worldin arms, but spare us civil war." CAPTION: Picture, Defenders of the Spanish republic (1936). Photograph from the National Portrait Gallery, London