Andrei Alexandrov-Agentov -- speechwriter, linguist and key Soviet foreign policy adviser under four Kremlin leaders -- has been retired, according to Soviet sources.

He has been replaced by Anatoly Cherniaev, one of the five deputies to Boris Ponomarev, chief of the international department of the Central Committee, Soviet sources said.

Western diplomats said that it is still not clear what effect the change will have on the Kremlin's foreign policy.

The switch, coming in the midst of an unusual level of activity in Soviet relations with the United States, Asia and Western Europe under Mikhail Gorbachev, signals the new Soviet leader's wish to handpick his own close foreign policy specialists, according to interpretations by various Soviet officials and western diplomatic sources.

Until now, Gorbachev's shake-up of Communist Party officials and senior bureaucrats in the Moscow-based ministries hardly has affected the field of Soviet foreign policy. Since Eduard Shevardnadze was named foreign minister in a surprise announcement last July, few changes among senior level foreign policy advisers or Foreign Ministry officials have taken place.

Cherniaev appeared in a picture with Gorbachev in the Soviet party newspaper Pravda last week. One Soviet official described him as an Americanist and English speaker, but little else is known of him in the Soviet capital's diplomatic community.

Alexandrov-Agentov served as a speechwriter and adviser to former Soviet leaders Leonid Brezhnev, Yuri Andropov and Konstantin Chernenko.

He has made countless appearances in interviews, speeches and meetings with Kremlin leaders, including one at the end of the U.S.-Soviet summit in Geneva, when he appeared on stage with the Soviet leader, wearing dark glasses. But in the Soviet Union, he is best remembered for another appearance: When Brezhnev, in a 1982 television broadcast from Baku, started reading a prepared text, Alexandrov-Agentov snatched the paper from him and handed him another, saying, "This is the right one."

Whenever Gorbachev met with foreigners, from his first major interview with Time magazine last August to his interview last Tuesday with the French Communist Party newspaper L'Humanite, Alexandrov-Agentov was constantly at his side.

But when Gorbachev met last Thursday with Sen. Edward M. Kennedy (D-Mass.), the veteran foreign policy expert was conspicuously absent. The senator had been told earlier that Alexandrov-Agentov had resigned, according to Kennedy aides who accompanied him here.

Alexandrov-Agentov speaks English, French and Swedish, western diplomatic sources here said. As a young diplomat in the 1940s, he served in the Soviet Embassy in Sweden. Since then, he has made a hobby of translating poems from Swedish to Russian.

After working in the Foreign Ministry's Scandinavia division, Alexandrov-Agentov served as a personal adviser to then-foreign minister Andrei Gromyko in the late 1950s. When Brezhnev came to power in the mid-1960s, Gromyko chose him to be the new Kremlin leader's principal foreign policy adviser.