Mikhail S. Gorbachev has won another political victory, gaining Communist Party approval to restructure the Politburo that once ruled the country. The Politburo now promises to play second fiddle to the separate government structure he also leads. The vote by the 28th Communist Party Congress on Monday also marks a new effort to reduce the ethnic unrest that is tearing the Soviet Union apart by including party leaders from the 15 Soviet republics on the Politburo, the party's ruling inner circle. The new body will have up to 23 members, nearly twice the 12 voting members on the old body, and many if not most of the faces should be new. The expansion and restructuring will accelerate the process that Gorbachev began after he was elected to a strengthened presidency in March, transferring power to a newly created Presidential Council _ a development that has angered such hard-line Politburo members as Yegor K. Ligachev and could squeeze them out of their jobs. Unlike the Politburo, whose members are elected by the party, members of the Presidential Council are appointed and dismissed by the president, along the lines of a Western-style cabinet. The Politburo, which formerly met once every Thursday, has been meeting only once a month since March, and has been concentrating on Communist Party rather than government issues. Since most of the Politburo members will reside in their home republics, the Politburo will continue to meet relatively infrequently and will not exercise as tight control over national affairs as the body has traditionally done. The duties of the government council have not been fully defined. The 16-man body consists of six voting members of the Politburo, including the prime minister, defense minister, foreign minister, the KGB chief, and Gorbachev's right-hand man, Alexander Yakovlev. Other members are the chief law enforcement official, a reform-minded economist, a crusading environmentalist and a workers' rights activist. Significantly, whereas nine of 12 men on the old Politburo were members of the ethnic Russian majority, the new Politburo will include a majority of non-Russians. And the Presidential Council contains five non-Russians. The new Politburo will include the heads of the party organizations in the 15 republics, most of whom are clamoring for greater control over political and economic decisions affecting their regions. Shortly after becoming general secretary of the Communist Party five years ago, Gorbachev sought to centralize his authority, but he has been driven to support greater regional autonomy by the independence drives of the three Baltic republics. Moreover, the largest Soviet republic, the Russian Federation, last month proclaimed its intent to seek greater control of its affairs under the leadership of its populist Communist president, Boris N. Yeltsin. Mostly recently, Gorbachev has embraced the idea of reconstituting the Soviet Union as a looser confederation of republics. The Politburo has had its ups and downs since it was created on the eve of the 1917 Bolshevik Revolution that swept the Communists to power. The first two Soviet leaders, Vladimir I. Lenin and Josef V. Stalin, exercised virtual one man rule, appointing aides and allies to the Politburo. Under Leonid Brezhnev, who ruled for 18 years until his death in 1982, the Politburo was a coalition that made all the key decisions. As Brezhnev and the other Politburo members weakened with age, the country lapsed into what Gorbachev has labeled the period of stagnation. The first Politburo consisted of seven Bolsheviks, among them Lenin, the founder of the Red Army Leon Trotsky, and the lesser-known Stalin. Following Lenin's death in 1924, Stalin eliminated Trotsky and other rivals from the ruling body. By the height of his power in 1952, he had expanded the membership to 25 voting members, all loyal aides. It also included 11 non-voting members. Nikita S. Khrushchev, who rose to power after Stalin's death in 1953, whittled the body to 15 voting and nine non-voting members. Although he instituted reforms, he tried to keep a tight personal grip on power, angering Politburo colleagues who tried unsuccessfully to oust him in 1957 and succeeded in 1964. Brezhnev, Khrushchev's successor, used the Politburo to forge a coalition among Soviet interest groups, such as the armed forces, the KGB, other government ministries and major industrial sectors, who held most of the dozen slots. He also included seven heads of republic parties as non-voting Politburo members, allowing them to run their regions in return for loyalty. Gorbachev and his allies argue that Brezhnev's system led to widescale corruption and blocked the transformation of the country into a modern industrial society.