The Soviet Union's satellite regimes in Eastern Europe reacted swiftly today to President Leonid Brezhnev's death, praising his contribution to detente and preparing periods of mourning.

As in the Soviet Union, official commentaries seemed designed to create an impression of stability and continuity in Moscow's policies. In private, however, senior officials eagerly awaited the naming of Brezhnev's successor in the knowledge that they could be vitally affected.

There was subdued public reaction to the death of the man who sent Soviet tanks into Czechoslovakia in 1968 to suppress a reform movement and later formulated the doctrine of "limited sovereignty" whereby all communist countries have a duty to act against a threat to socialism in any one of them.

Brezhnev is remembered in Eastern Europe with mixed emotions for presiding over an unprecedented military buildup, but he also allowed greater contacts between East and West in the late '70s.

Even his role in the suppression of the independent Solidarity trade union in Poland is not clear-cut. Most Poles believe that intensive Soviet pressure was a vital factor in the military takeover last December, but also credit Brezhnev with avoiding direct intervention by the Red Army.

Several passers-by interviewed here commented that they hoped that Brezhnev's death would not make "matters any worse than they already are." As one elderly woman remarked: "Well, he has his assistants, doesn't he? In any case, he was only a symbol. Someone else will take over and pursue much the same kind of policies."

Polish attitudes toward Kremlin leaders are colored by centuries of anti-Russian hostility. By contrast, in Bulgaria, which has the strongest historical and cultural affinity to Russia, official reports said many workers "spontaneously" laid down their tools as a mark of respect for Brezhnev.

Past changes in Moscow have resulted in a delayed reaction in Eastern Europe. The death of Joseph Stalin in 1953, for example, led to a political process of de-Stalinization that helped create the atmosphere for the 1956 upheavals in Hungary and Poland.

The Czechoslovak reform movement of 1968, meanwhile, was made possible by Brezhnev's giving the green light for the replacement of the old Stalinist, Antonin Novotny, by Alexander Dubcek.

Few political analysts in Eastern Europe believe that Brezhnev's death will produce such dramatic consequences on account of his rule by consensus. It is worth noting, however, that, with the exception of Poland's 59-year-old Gen. Wojciech Jaruzelski, the Soviet Bloc leaders are about Brezhnev's age. In the event of a power struggle, Moscow could signal the choice of their successors.

Czechoslovakia's Gustav Husak and East Germany's Erich Honecker have perhaps the closest ties to Brezhnev of the bloc leaders. It will be particularly important for them to establish good relations with the next first secretary of the Soviet Communist Party.

Over the past year, politicians throughout the bloc began searching for clues to the succession. Their analysis appears to coincide broadly with that of Western experts who believe that a change of generations in a few years could be even more important than the immediate transfer of power.

"The Kremlin Wall is almost as much an Iron Curtain for us as it is for you," a senior Hungarian official remarked recently. He said that even from their relatively privileged position, it was impossible for Soviet Bloc leaders to divine the Kremlin's intentions.