Imagine that you are the representative of a weak East European country struggling to maintain its independence from the Kremlin. The Soviet defense minister casually mentions in a conversation that the Soviet Union's armed forces are extremely powerful and could subjugate your country in three days if necessary. How do you reply?

If you are Veljko Micunovic, Yugoslav ambassador in Moscow from 1956 to 1958, you tell him that even when the Germans were at the height of their power during the second World War, they were unable to conquer Yugoslavia in four years - let alone three days.

This is not a hypothetical case. According to the ambassador's diaries which have just been published here, this model report was delivered to Marshal of the Soviet Union Gheorgi Zhukov in June 1957.

Ambassador Micunovic's remarkably frank memories, which are rapidly becoming a best-seller in Yugoslavia, have already drawn angry protests from the Soviet Union. Soviet journalists in Belgrade privately describe "Moscow Years", which paints a picture of virtually continual pressure on Yugoslavia by Soviet leaders as " a dreadful book" and "anti-Soviet." it is also understood that complaints have been made to the Yugoslav Foreign Ministry, although has not been confirmed officially.

The chief interest of the diaries is that they reveal, in greater detail than ever before, the underlying premises to relations between the Soviet Union and Yugoslavia: the first country of socialism and the heretic which broke away from the Soviet bloc in 1948.

With refreshing candor, Micunovic provides a unique glimpse of what lies beneath the smiles of Soviet and Yugoslav leaders at diplomatic receptions and the reassuring formulas of their official communiques.

The events he describes took place two decades ago, a period marked by alternate honeymoons and crises in Sovet-Yugoslav relations. Much has happened since then, in both countries, but as Micunovic writes in his forward: "The basis of our relations has not changed."

The message of "Moscow Years" seems to be that, whatever is said in public Yugoslav leaders believe that the Kremlin's ultimate aim was, and remains, to bring Yugoslovia back to the Soviet bloc.

Micunovic cites three reasons why the Soviet leader should want to subjugate Yugoslovia. First, this would make the Soviet Union a Mediterranean power for the first time in its history. Second, it would create a monolithic socialist bloc in Europe under complete Soviet control. Third, it would put an end to talk about "independence and equality" in relations between Communist countries, an idea first raised by the Yugoslavs.

In the view of the Soviet leaders, Micunovic wrote in his diary on March 21, 1956 a socialist camp without Yugoslavia remains an unfinished creation, both politically and territorially, and is subject to erosion."

There seems little doubt that "Moscow Days" reflects the views of Yugoslav leaders who want to emphasize that Yugoslavia will not bow to external presure, even after the death of President Tito, 85.

Micunovic, now retired, was one of Yugoslavia's most distinguished diplomats. He served as ambassador to Washington from 1962 to 1967 and was for three years a member of Yugoslavia's collective federal presidency.

It is also widely believed in Belgrade that, in view of the predictable furor it would cause in the Kremlin, permission to write and publish the book must have been granted at a very high level, even though Yugoslav officials say it was a private matter between Micunovic and his publisher.

Among the many passages likely to infuriate the Russians is criticism of Mikhail Suslov, still a very influential member of the Soviet Politburo.

"When it is a question of talking to Suslov all possibility of agreement between Yugoslavia and Russian can be excluded," Micunovic writes.

He then describes a marvelous scene in which he is summoned to see Suslov to explain a new Yugoslav Communist Party program which the Russians consider dangerously revisionist. Standing behind a desk piled high with documents and papers, the chief Soviet ideologist receives him like a headmaster scolding a particularly disobedient child.

Recalls Micunovic: "Suslov looked so mad and furious that he seemed unable to restrain himself. He didn't even offer me a chair . . . He behaved so angrily that conversation was out of the question. I listened to his attacks on Yugoslavia, one after another. They were uttered as though I, or some other Yugoslav, had personally insulted him or his family and was being called to account for it.

"Still standing, I told Suslov that we were talking about a Yugoslav party program and not a Soviet one. I indicated my readiness to end the conversation and walk out. Suslov then offered me a seat and listened to me."

Foreign diplomats in Moscow today would envy Micunovic for his access to Soviet leaders. He saw Khrushchev every other week, sometimes for conversations lasting as long as six hours at which extra ordinary confidences were revealed. It was atime when the Soviet leadership was opening up to the outside world and wooing Yugoslavia was an essential part of the strategy.

Valuable historical material contained in the diaries includes the first detailed account of a top-secret meeting between Khrushchev and Tito the night before Soviet troops invaded Hungary in November 1956. The meeting took place on the Yugoslav leader's private island of Brioni. Only six people were present, including Micunovic, and no record of their 10-hour conversation was ever made.

Micunovic describes how Khrushchev, who by that time had already decided to go ahead with the invasion, arrived in Brioni airsick after a very bumpy flight in a twin-engined plane from Bulgaria. Discusing who should replace Imre Nagy as Hungarian leader, the Yugoslavs supported the claims of the present leader Janos Kadar on the grounds that he was likely to be more acceptable to public opinion because of the time he had spent in prison.

Many of the anti-Yugoslav trades Micunovic was subjected to by Russian leaders stemmed from essentially trivial incidents, which nevertheless hid a deeper Soviet irritation with Yugoslovia. When the Yugoslav press failed to carry the full text of a speech by Khrushchev in reply to Tito, it was depicted as a direct affront to the Soviet Union and Khrushchev personally.

The Soviet president, Klement Voroshilov, threateningly asked Micunovic after this incident: "Do you know what happens to the Poles, Czechs, or Hungarians, if they do that sort of thing to us? The answer was left to hsi imagination.

It makes one wonder what the present Yugoslav ambassador in Moscow is writing in his diary right now as the result of the publication of Micunovic's book.