The Communist Party Central Committee retired President Andrei Gromyko and three other members from the ruling Politburo in a major shakeup Friday that also weakened a key rival of Soviet leader Mikhail Gorbachev.

"The Soviet Communist Party Central Committee plenum today met the requests of a number of party leaders to be relieved of their posts in connection with their retirement on pensions," committee member Vadim Medvedev said.Gromyko, 79, asked to be retired from his position in the Politburo and his request was granted, Medvedev told reporters after the hastily called plenum of the policymaking body convened in Moscow.

He retains the largely ceremonial post of the presidency, at least until a meeting Saturday of the Supreme Soviet, the body responsible for the government position.

Yegor Ligachev, seen as Gorbachev's chief rival in the Politburo, was stripped of the prestigious ideology portfolio and assigned to the newly created position of chairman of the Agriculture Commission.

Gorbachev praised Gromyko, who faithfully served Kremlin leaders during a half-century-old career from Josef Stalin to Gorbachev but said the changes ordered by the Central Committee were necessary to streamline the party apparatus.

"Generally speaking it has been a rich political life," Gorbachev said of Gromyko. "I would like to thank him on behalf of my colleagues in the Politburo for the great work and faithful service for the party and the state."

Gromyko, the only other person permitted to address the plenum, said, "The only sensible decision was for me to retire."

Gromyko served as foreign minister for nearly three decades until 1985 when Gorbachev, less than four months in power, named him to the largely ceremonial position of president, in part to give a new face to Soviet foreign policy.

The Central Committee session was hastily called by Gorbachev in an apparent bid to revive momentum in his program of economic restructuring, called perestroika, and to make deep cuts in the party bureaucracy.

The suddenness of the meeting and the conspicuous one-month public absence of Ligachev had sparked expectation of major Politburo changes. Diplomats said Gorbachev was eager to rid the Politburo of leftovers from the conservative era of the late leader Leonid Brezhnev.

Mikhail Solomentsev, 70, a full member of the Politburo was relieved of his duties. Vladimir Dolgikh, 63, and Pyotr Demichev, 70, were removed from their positions as alternate, or non-voting members of the Politburo.

Anatoly Dobrynin, 68, Soviet ambassador to the United States for 24 years, was retired at his request from his position as a secretary of the Central Committee, Medvedev said.

Medvedev was made a full voting member of the Politburo and two other Central Committee secretaries, Alexandra Biryukova and Anatoly Lukyanov, were appointed alternate members of the ruling body.