PRAGUE, DEC. 19 -- Eight months after Soviet leader Mikhail Gorbachev challenged Eastern Europe to reform its economic and political affairs, the region is in a ferment of upheavals, reform plans, internal power struggles and public debates that are both a product of the Gorbachev era and yet are relatively free from Moscow's direct manipulation.

In the last four months, all six of Moscow's Warsaw Pact allies have experienced dramatic political events that seemed to mark a break with previous periods of stagnation. Although the developments and their causes have varied from country to country, the overall effect has been to propel this region toward the dynamic of change Gorbachev has sought to create around the communist world.

The latest shift came here this week as veteran Czechoslovak leader Gustav Husak, a symbol of orthodoxy throughout the Eastern Bloc, retired as party chief. Although his successor, Milos Jakes, pledged continuity, the retirement represents the first step for any real change in this tightly controlled country.

Husak's move added to a burst of activity in Eastern Europe unprecedented in its breadth since the years 1968 and 1956, when protests and reform movements erupted in several countries and eventually ended with Soviet invasions.

Last month, riots erupted in the Romanian city of Brasov, providing the first serious blow to the neo-Stalinist dictatorship of Nicolae Ceausescu. In Poland, communist authorities announced a major economic and political reform plan, held a referendum on it, then made the unprecedented announcement that they had failed to win.

In Hungary, the new prime minister, Karoly Grosz, an aggressive imitator of Gorbachev's style, announced a government reorganization and a policy shake-up that strengthened his image as the country's de facto manager, slowly edging the aged party leader Janos Kadar toward retirement.

Bulgarian party leader Todor Zhivkov announced his own radical and seemingly eccentric reform plans. And East German leader Erich Honecker, though resisting the Moscow-inspired policy trends, made the historic visit to West Germany that the Kremlin had so often blocked in the past.

Although Gorbachev may have had a role in some of these developments, not all of the political shifts have appeared favorable for Moscow. In the case of Romania, the riots and possible weakening of Ceausescu have had only a slight relation to Gorbachev's reform drive.

Much as Gorbachev has appeared to be slowly and with difficulty pushing the Soviet Union toward economic and political modernization, Eastern Europe is now being tugged in the same direction.

"There's no script, no monolithic movement," said one western diplomat in Warsaw. "But everywhere you look, something is happening. And that in itself is a real change."

The diverse character of the change seems close to what Gorbachev prescribed in a landmark speech here in April. Forswearing Moscow's role as a model for Eastern Europe, he urged the region's leaders to seek out their own new solutions for communism. The Soviet Union could tolerate diversity among its allies, he indicated, but not their further stagnation.

At the same time, most of the new policies under way in Poland, Hungary, Czechoslovakia and Bulgaria have been broadly linked with Gorbachev's themes of perestroika, or economic restructuring, and glasnost, or political openness. Differences among these countries to some extent reflect a healthy effort to adapt the dominant model for changing Stalinist socialism to national conditions.

Now that change has begun, the crucial question in Eastern Europe, as in the Soviet Union, is whether policies of liberalization and modernization will overcome the stiff initial resistance they have encountered and whether they will eventually lead to real improvements in living standards and human rights.

In that sense, recent events in Eastern Europe have been as ambivalent and cloudy as those in Moscow. While both Poland and Hungary launched aggressive new policy programs this fall, Grosz in Hungary and Gen. Wojciech Jaruzelski in Poland have since had to acknowledge strong public resistance to price rises and other austerity measures.

In Czechoslovakia, a program of reforms put together in the last year of Husak's administration has been unable to win the full support of party apparatchiks still traumatized by the 1968 "Prague Spring." And Zhivkov in Bulgaria seems stymied in pursuing his own new policy framework, recently postponing a party conference that was to consider it.

A major defeat for the new policies in Hungary or Poland could be a serious blow to Gorbachev as well. But the Soviet leader may have a key advantage in the region: the broad generational turnover of communist leadership that, inaugurated by Husak this week, can be expected to spread to five other East European countries within the next five years.

East Germany's Honecker, like Husak, is nearing his 75th birthday, while Hungary's Kadar and Bulgaria's Zhivkov have already passed that age. Ceausescu is 69 but may have health problems. Even Poland's Jaruzelski, only 64 and nominally Gorbachev's closest East European ally, may face a serious political threat if his new economic reform fails next year.

If Husak's retirement and the slow fading of Kadar in Hungary are any indication, the East European leadership transition will be orderly, bereft of overt Soviet intervention and yet clearly in line with Gorbachev's interests. As a potential successor to Kadar, Grosz has projected the image of a would-be political clone of the Soviet leader.

Even in Prague, where Jakes has initially pledged allegiance to Husak's conservative line, Czechoslovak observers said the new leader will probably align his policy closer to that of Gorbachev, if only to ensure his own political survival.

"Jakes is a man who has always been good at following a higher leader," said Jiri Dienstbier, a dissident. "And the only leader he has above him now is Gorbachev."