Soviet leader ousts prominent critic. Toppling of powerful party boss could boost Gorbachev's reform

One of the last of the top Brezhnev-era party bosses has been replaced by a Gorbachev-style reformer. Dinmukhamed Kunayev, a friend and prot'eg'e of former Soviet leader Leonid Brezhnev, was relieved of his position as first secretary of the Kazakhstan Communist Party yesterday, the official Soviet news agency Tass announced.

His retirement means that he will soon lose his position on the nation's 12-man ruling Politburo - something that Soviet leader Mikhail Gorbachev has been trying to bring about since he came to power in March 1985.

The retirement of Mr. Kunayev, who is believed to have had little love for Mr. Gorbachev, comes at an important time for the Soviet leader: The repeated delays in the calling of a plenary session of the Communist Party Central Committee had led to speculation that Gorbachev's reform program was running into serious trouble. Tass said Kunayev was leaving at his own request. But there is little doubt that his departure is the climax of a long and carefully planned operation.

His replacement is Gennady Kolbin, who since December 1983 has been party secretary of the Ulyanovsk region, about 500 miles southeast of Moscow. During the June plenum of the Central Committee, the Ulyanovsk party organization was one of a handful singled out for praise for its energy and efficiency. Later the party newspaper Pravda described at length how Mr. Kolbin had cleaned up the Ulyanovsk party structure. Officials in his own area have pointedly described him to visitors as a leader ``in the Gorbachev mold.''

The appointment of Kolbin, an ethnic Russian, breaks the Kremlin's tradition of giving the party leadership of a republic to a representative of the local nationality.

Kunayev, 74, had been leader of the Kazakhstan party since 1964 and a candidate member of the Communist Party Politburo from 1966 until his appointment as a voting member in 1971. Kunayev and another regional leader, Ukrainian party chief Vladimir Shcherbitsky, have often been identified as Gorbachev's key opponents in the Politburo. But the two men are not the only source of opposition. More serious problems are caused by the tens of thousands of officials at all levels of the party structure who see Gorbachev's reforms as a threat to their comfortable life styles. Both men control large party machines - the Ukraine has 3 million members - and thus have considerable patronage at their disposal.

Gorbachev began to move in on Kunayev earlier this year. In February, two-thirds of the Kazakhstan party committee were replaced. Around the same time, some 500 officials were reportedly removed from their positions. Several months later, Kazakhstan's transport minister was arrested on corruption charges. Similar moves have been made against Shcherbitsky's supporters. But the Ukrainian leader has proved difficult to dislodge.