How an ill-considered pact brought war, dictatorship, and the bomb; The Fateful Alliance: France, Russia, and the Coming of the First World War, by George F. Kennan. New York: Pantheon Books. 300 pp. $18.95.

Unfortunately, the worn cliche that coming events cast their shadows ahead of them is all too often false. Or, at the least, such shadows are misinterpreted with tragic results.

So it was with what author Kennan views as one of the most fateful treaties of human history - the 1894 military alliance between republican France and czarist Russia. To the eventual effects of this treaty, he argues with considerable persuasiveness, can be traced World War I with its 35 million dead; the establishment of a Communist state in Russia; the diplomatic mistakes which would result in the triumph of Nazism in Germany and World War II; the Marxist engulfing of Eastern Europe; and, indeed, the first use of nuclear weapons.

If this seems like a fantastic array of consequences to attribute to a single scrap of paper, Kennan presents a strong rationale for this case.

Not only could no one in the last decade of the 19th century foresee the enormously tragic results of this alliance, but as Kennan shows us, the alliance was, at so many points, the result of gross stupidity, petty motives, small personal prejudices, the inexcusable failure of diplomatic wisdom, and misguided ambition. All of the major continental nations - Austria, France, Germany, Italy , and Russia - which would eventually be caught up in the drowning undertow from this single event, were in part responsible for it. Yet the major protagonists were France, Germany, and Russia.

In that last decade of the century, each of these three was in a mood ripe for mistakes. In 1870 the French government had foolishly fallen into a diplomatic trap laid by German Chancellor Bismarck and, trying to extricate itself, went to war, was badly beaten, and lost the provinces of Alsace and Lorraine. By 1890 French opinion was increasingly chauvinistic and revanchist.

Germany, meanwhile, had dropped the wise and, by then, cautious Bismarck and had incomprehensibly refused to renew the so-called Reinsurance Treaty with Russia, neutralizing the latter in case of a German war with France.

And in Russia, Czar Alexander III had become increasingly anti-German through dislike of his German cousin, Kaiser Wilhelm II, and his belief that Germany was frustrating Russian ambitions in the Balkans. Because of his Czarina, Princess Dagmar of Denmark, he bitterly resented the earlier loss of the Danish duchies of Schleswig and Holstein to Prussia.

France and Russia therefore grew increasingly convinced that their quite distinct national ambitions would best be served by an alliance.

Had, in fact, this treaty been wisely and carefully drawn, its terrible consequences might still have been avoided.

But its main clause was disastrous. It stated that, if there were even a partial military mobilization by any member of the Triple Alliance - Austria-Hungary, Germany, and Italy - France and Russia were to immediately and without further consultation or diplomatic effort begin hostilities against the Triple Alliance. In other words, if even weak Italy were to begin mobilizing or if Austria were to take up arms in the Balkans, France and Russia were obligated to attack Germany.

This is, in a sense, what happened in the summer of 1914, when Austria determined to punish Serbia for the assassination of Archduke Ferdinand. Although popular opinion still holds otherwise, the Germany of 1914, being ''a satiated power,'' had little reason to wish to go to war. (In fact, Berlin at first sought to restrain its Austrian ally.) By then, however, the author tells us, ''most influential people in France, as elsewhere, accepted another European war as ultimately inevitable.'' The terrible toll of consequences began.

For the historian, the strength of this book lies in the often extreme detail with which the author traces the evolution of the Franco-Russian treaty. To other readers this detail may seem excessive. It is written with Kennan's vast knowledge and some six decades of intimate familiarity with international diplomacy. It is a valuable and sobering reminder of how indescribably important it is that the official relations between and among nations be conducted with caution, with foresight, and, to the degree possible, with goodwill.