MOSCOW, MAY 28 -- Populist Soviet politician Boris Yeltsin today offered the Communist Party apparatus a share in a Russian coalition government if they agree to support his bid to become president of the Russian federation, the largest and most populous of the Soviet Union's 15 republics.

Following two inconclusive ballots, members of the Russian legislature are scheduled to take a third vote on the presidency Tuesday as Soviet leader Mikhail Gorbachev leaves Moscow for Canada and his meeting later in the week with President Bush.

Yeltsin's election to the post would mark a major setback for Gorbachev, who has accused the former Moscow Communist Party chief of wanting to turn Russia away from socialism and break up the Soviet Union.

In a last-ditch attempt to deny Yeltsin the office, Communist leaders resurrected the candidacy of Alexander Vlasov, a non-voting member of the Communist Party's ruling Politburo and a close Gorbachev ally. Vlasov withdrew from the race Friday when it appeared that he had no chance of winning.

Russian legislators said the odds were still stacked against Vlasov, who has made little public impression despite the fact that he held the post of Russian premier for the last two years. But the Kremlin leadership seems determined try any means to keep Yeltsin out of the post, which could make him the most influential politician in the country after Gorbachev.

Yeltsin, who resigned from the Soviet hierarchy in disgrace two years ago, has called for constitutional changes to guarantee the Russian federation political and economic autonomy. His political program calls for power to be devolved from the center to the republics, allowing the Russian government to develop its own domestic and foreign policies with little interference by the Kremlin.

If Yeltsin achieved his goal, the role of the Soviet government and of Gorbachev as president of the country would be diminished. The central authorities in effect would be reduced to coordinating relations among 15 powerful and assertive republics. As part of a governing coalition, however, Yeltsin would have to modify his program.

While resurrecting Vlasov's candidacy, the party abruptly dropped its support of Ivan Polozkov, a conservative apparatchik from the southern Russian city of Krasnodar who was the official candidate in the first two rounds of voting.

Yeltsin topped the ballot on Friday and Saturday, but was 28 votes short of the required 531-vote majority.

At the start of today's legislative session, acting chairman Vasili Kazakov provoked an uproar when he suggested that both Yeltsin and Polozkov had a moral duty to withdraw from the contest. Radical-reformist members stormed the podium to protest, denouncing Kazakov as a creature of the ruling apparatus.

Yeltsin then took the floor to offer his opponents a "mechanism" whereby he would take over the presidency while other senior posts were distributed to party conservatives. "Whether I win or lose, I'll be ready for contacts, so proposals for the composition of the leadership can be discussed," he declared.