What caused the fall of Premier Khrushchev? The relevant factors are as obscure as they could be without becoming entirely mysterious. But there are indications of the constellation of events that brought his demise. Khrushchev seems to have been very securely in power by 1958; the years that followed brought an increasing burden of setbacks which shook his hold.

On the international scene, Berlin was a serious defeat. Khrushchev evidently thought he could force the Allies out of the city with a series of threats following hard on the Sputnik successes in space. He was forced to back down. The Cuba confrontation of October 1962 was an even more paralyzing setback. And within the Communist camp, the Premier's handling of relations with China had allowed a dispute to swell into uncomradely hostility. He had planned to stage a climactic meeting of the world's Communist parties in Moscow this December to condemn the Chinese, but the fraternal parties dragged their feet so that the meeting threatened to be a fiasco. Another terrible defeat was the disintegration of Soviet power over European Communism culminating in the Italian party's declaration of independence, the formerly abject French party's similar declaration, and the virtual revolt of the heretofore grovelling Rumanians.

Domestic affairs did not go much better. After 1958, agricultural output fell fairly steadily. In 1963 there was a catastrophically bad harvest, and the Soviet Union had to spend hoarded reserves of currency on the world market to buy millions of tons of grain. There were industrial difficulties in allocation of resources: the military pressed for its habitual lion's share while the technocrats demanded the same resources in order to meet Premier Khrushchev's exuberant promises of advances in consumer goods.

Then there were the less tangible causes of discontent. Russia's prestige has been suffering abroad. The revolutionaries are turning to the Chinese, the mixed-economy nations are on the whole sticking with the West, and the neutralists spurn the Russians as well as the Americans. Caught between the advances of a more revolutionary Communism and the responsibilities of nuclear power leadership, Premier Khrushchev was almost inevitably damned for what he did do, and damned for what he didn't.

Finally, of course, the Premier was getting old. He was spending less time with his hands on the controls and placing more faith in his lieutenants. Leonid I. Brezhnev owed his entire career to Khrushchev; Aleksei N. Kosygin owed him the second chance so rarely granted in Soviet political life. One day, they seem to have decided that they had sufficient support to oust the old man vacationing at his Black Sea resort. They did.

It is impossible to guess what will be the result of the succession in the coming years. The Soviet ambassador is reported to have assured President Johnson that the policy of detente will be continued and even strengthened. But it is possible that the leadership is only playing for time.

It would be logical for the new leaders to initiate exploratory talks with China to see if the ideological rift can be healed. Yet this brings up an obvious point--the new Soviet rulers face precisely the same problems that Khrushchev faced. Making up with Communist China while continuing a policy of detente with the West will not get any easier. But the alternative they face remains the same: that of nuclear disaster.

Beyond this, we must wait for the speeches and changes in personnel introduced by the new rulers to determine the regime's policies and to learn whether one of the two men must rise as the single master of the Soviet Union.

At Harvard, meanwhile, a great deal of rethinking has to be done. One of the strong assumptions of Soviet studies here has been that once a Soviet dictator is firmly entrenched in power he cannot be removed from within except as a result of grave mental disability or death. This unexpected succession throws the neatly drawn "characteristics of totalitarian dictatorship" out of order.

Yet the succession reaffirms the fundamental skepticism with which every student of Soviet affairs at Harvard should begin: no matter what rules you make for patterns of Soviet conduct, the Russians will eventually break them. Khrushchev's downfall renews the humility with which even the best scholars have learned to approach predictions about the gigantic power on the other side of the world.