Bulgaria Responds to Pressure for Change

THE winds of change in Eastern Europe have swept over Bulgaria, whose veteran Communist leader Todor Zhivkov resigned Friday. Mr. Zhivkov was replaced by a close colleague, who immediately promised reforms.

The change in Bulgaria leaves only two remaining Stalinist bastions in Eastern Europe, Nicolae Ceausescu's Romania and Milos Jakes'sCzechoslovakia. In neither country are there signs of quick change.

Petar Mladenov, Bulgaria's new party boss, is 53 years old. He has been a member of the ruling Politburo for almost 12 years and Bulgaria's foreign minister since 1971. A quick telegram from Moscow, in which Soviet leader Mikhail Gorbachev heartily congratulated his ``dear comrade'' Mr. Mladenov, created no doubt that the leadership change had Moscow's blessing.

Mladenov immediately stated that there was no alternative to reforms, but that they should take place within the socialist structure.

Observers could not immediately say how far these changes might go, but they did not exclude more resignations in the party leadership.

The 78-year-old Mr. Zhivkov had ruled his country for 35 years, longer than anybody else in the East bloc.

Bulgaria, with 9 million inhabitants and long considered the Soviet Union's most loyal ally in the Communist bloc, was last week the scene of rare political demonstrations by opposition groups, led by a group called Ecoglasnost. The demonstrators demanded a cleaner environment and also democracy, but they were harshly dealt with by Zhivkov's police.

Meanwhile, nobody seems to threaten Mr. Ceausescu's total grip on power in Romania. Romania has no social organizations to create an alternative to Ceausescu.

In Czechoslovakia, the hard-liners who took over after the country's 1968 uprising seem firmly in power, and they show no willingness for change or a dialogue with the opposition groups. However, many observers think change must soon come also to Czechoslovakia, particularly in wake of the radical transformations in neighboring East Germany, with which Czechoslovakia for so long has had close ties.