THAT WAS A shocking report by The Post's Moscow correspondent, Dusko Doder, about a new, crudely anti-Semitic book published in the Soviet Union. The shocking part was not so much the content --gutter racism in pseudo-scholarly guise is, unfortunately, not the monopoly of any one country. It was to have such a book emerge and be hailed in a country where no book is published without state sanction. The book and the evident campaign of which it is a part indicate a readiness on the part of the Soviet authorities to use anti-Semitism as an instrument of official policy. This is being done notwithstanding the offense that publication was bound to give to decent people in the Soviet Union and abroad.

Precisely what official Kremlin purpose is served by a book like "The Class Essence of Zionism"? One possibility is to stir anti-Semitism and anti-Zionism--the book appears to make no practical distinction between the two--to keep Soviet Jews from trying to exercise their right to emigrate; no Jewish emigration is being permitted these days. A second is to flash an additional caution to would-be individual dissidents and members of other non-Russian ethnic groups in the Soviet Union. A third is to buy a little cheap popularity with certain vulnerable elements in Soviet society.

Or maybe it is simply a police game or an internal political ploy. One cannot know these things. In particular, one does not know how Yuri Andropov fits in. As head of the KGB for 15 years before he became the top Soviet leader, he was deeply identified with policy toward Jews.

The only good thing about this book is that some Soviets are among those repelled by it. Reporter Doder found it was too much even for one of the members of a committee the authorities recently organized to advance the official "anti-Zionist" campaign. At a press conference, one person on the committee evaded a question about the book, but another said: "This committee in the future will fight against wild and wrong accusations in books which have been written by a few authors and unfortunately have been permitted to be published."

Let there be no confusion about the complete control the Kremlin wields over an aspect of policy so domestically and internationally sensitive as the treatment of minorities. Just the other day Yuri Andropov won a nice little burst of Western applause for allowing the emigration of 15 Pentecostalists who had sought exit visas for 20-plus years; five of them had spent almost five years in the basement of the American Embassy in Moscow. He could end the Kremlin's latest sponsorship of anti-Semitism with one phone call.