MOSCOW -- A few months ago, Phil Collins and his rock band Genesis gave an outdoor concert on the western side of the Berlin Wall. Hundreds of East Berliners gathered near the Brandenburg Gate, where they could overhear every note. And as they listened, the crowd chanted the name of the man who has come to represent reform in the communist world and has begun to change the relationship between the Soviet Union and their own country: "Gor-ba-chev! Gor-ba-chev!"

For East Germany, where dissent is rarely tolerated, that evening in June -- marked by mass arrests and violent clashes between police and protesters -- was a clear demonstration of impatience with the pace of reform in that country.

In the past year, Soviet leader Mikhail Gorbachev's calls for increased freedom of expression and economic reconstruction have provoked important shifts in the relationships among the Soviet Union and the countries of Eastern Europe. Where once the Soviet Union was the dominant force of conservatism, stamping out grass-roots activism in Hungary and Czechoslovakia, it is now regarded as an active crusader for change in the communist world.

At the same time, Gorbachev has tried to persuade rather than impose, allowing for differences among states, but also causing a mood of uncertainty among the various leaders. More liberal regimes, such as Hungary's, struggle to determine the outer limits of permissible reform, while more conservative ones, such as Czechoslovakia's, try to figure out if there are minimum requirements of change they must fulfill.

While the Hungarian-style quest for bolder political and economic reforms appears to pose serious risks for the Soviet leadership, experts in Moscow regard the push for radical change as the best hedge against the economic slump that persists in much of Eastern Europe. "In the end," said one western specialist in East Bloc affairs, "the whole region should be stronger and not weaker."

The ferment became evident last April when Gorbachev appeared at the site of the most recent armed conflict between Soviet troops and Central Europeans. In Prague, where 19 years ago Soviet tanks rolled through the streets and chilled the Czechoslovak "spring," the Kremlin leader called for a new era of glasnost, or "openness," across Central Europe. With that speech he seemed to loosen the ideological hammerlock Moscow has held over the region for 40 years. Part of glasnost, he suggested, was at least a degree of national autonomy.

"We do not think that we know the best answers to all questions," Gorbachev said in Prague. "We are far from asking anyone to copy us. Every socialist country is unique, and fraternal parties shape their policies proceeding from national specifics."

Gorbachev's speech has reverberated in recent months throughout most of the East Bloc, encouraging displays of independence rarely seen among Moscow's satellites.

East Germans, including communist party leader Erich Honecker, responded with the biggest rush of visits to West Germany since a fortified barbed-wire fence was erected between the two German states. The Poles reacted with a sudden and emotional outpouring of long-held resentments against the Soviet Union's treatment of Poland during World War II.

But last week, the Polish government followed Moscow's lead by unveiling the most far-reaching reform

Jackson Diehl, The Washington Post's correspondent for Eastern Europe based in Warsaw, spent a month recently in Moscow. During that time, Gary Lee, The Post's Moscow bureau chief, traveled through Poland, Romania, Yugoslavia and Hungary and earlier had visited East Germany. Their reporting, based on this exchange of assignments, produced a two-part series on the changing relationship between the Soviet Union and its Eastern European allies.

measures since the rise of the Solidarity trade union movement in 1980.

The Bulgarians and the Hungarians also have moved quickly to seize the opening provided by Gorbachev. In August and September, respectively, party leaders in Sofia and Budapest introduced extensive packages of economic and political changes.

Still, throughout much of Central Europe, memories of one Soviet crackdown or another haunt the spirit of glasnost.

"I was by chance in Prague when the Soviet tanks rolled in," a leading Yugoslav banker recalled recently. "It is something that you only want to see once."

Besides the daunting presence of a million Warsaw Pact troops scattered across Eastern Europe, other realities darken the mood of reform. Several of the ruling communist parties of the bloc, including those of East Germany and Czechoslovakia, are dominated by an aging generation of conservative leaders, and they barely disguise their distaste for Gorbachev's more progressive policies. Their response to his call has been modest.

But many Eastern Europeans, such as those at the Berlin Wall last June, seem inspired by Gorbachev and eager for a new wave of reform. Some Poles, for example, have practically canonized the Kremlin leader in a new popular Polish rock ballad. "Spring blows from the East," it goes, "Mikhail, the renewer. Truth more truer."

Moreover, the Kremlin's new leniency has sparked a debate over how far to take the new-found freedom that Moscow has given, according to interviews with intellectuals, party officials and dissidents in Poland, Hungary, Romania, Yugoslavia and East Germany.

The consensus among them is that Gorbachev's reform drive has captured the imagination of much of Eastern Europe. They believe that the very nature of government in several of the socialist countries will become subject to fundamental changes as the Kremlin leader pursues his campaign, despite considerable resistance from the entrenched bureaucracy.

The process could erode party rule throughout the region as well as the Soviet Union's own leadership role. In an interview in Budapest, Hungarian economist Martin Tardos predicted that the governing parties of the region will eventually go the way of the British monarchy. "They may not lose power altogether," he said, "but they are probably destined to concede more and more of it to parliaments."

Hungary and Poland have already taken the first steps in this direction.

In Hungary, a plan to strengthen the role of the more populist-minded parliamentary government already has begun and is expected to go much further, according to interviews with senior Hungarian officials.

In a fractious session of the Hungarian parliament in late September, legislators endorsed the socialist bloc's first comprehensive personal income and value-added tax code. They also passed a package of controversial austerity measures, including deep reductions in state subsidies on such basics as bread and milk.

Last Thursday, Poland's leadership introduced several new reforms, including a wage and price shake-up, along with major new incentives for private enterprise. The plan also calls for measures to buttress the role of the second chamber of the Polish parliament and to broaden the role of nonparty political associations and action groups.

In Poland, glasnost also has brought together local and Soviet historians in an effort to fill in blank spots in official Polish-Soviet history. The joint project, approved in a meeting between Gorbachev and Polish leader Wojciech Jaruzelski shortly after the Kremlin leader's speech in Prague, is expected to publicize the Polish bloodshed by Soviet troops during World War II and other subjects so embarrassing to Soviet rulers that they have been kept out of history books in both countries.

And yet activists and intellectuals in both Budapest and Warsaw are urging even bolder initiatives.

Polish intellectuals are trying to find ways to revive Solidarity, the union crushed and banned under Jaruzelski. The Polish leader still opposes Solidarity.

In opposing Solidarity, historian Bronislaw Geremek said in an interview in Warsaw, Jaruzelski is "ignoring the best opportunity for radical reform Poland has ever had. The wind is blowing from the East. We cannot afford to lose this opportunity."

The Polish leader also is risking early failure for his new reforms, Polish economist Jan Mujzel said recently, adding, "They can hardly work well without some kind of cooperation with labor organizations."

In Hungary, too, the atmosphere of renewal appears to be resuscitating the very reforms of 1968, initially introduced by the party, but quickly stymied by the violent Soviet crackdown in neighboring Czechoslovakia.

The Hungarian reforms, which offered a comprehensive package of work, investment and social options to the public, were designed to democratize political as well as economic life, Tardos, the economist, said. "The events in Prague in 1968 deformed our movement into a purely economic one. We are still suffering the consequences. Hopefully, we now have a chance to revive the political aspects."

While Warsaw and Budapest debate the pace and content of reforms, their neighboring conservative East Bloc states Czechoslovakia and Romania appear to be avoiding significant change altogether. "They are doing the barest minimum required to keep from being totally out of sync with Moscow," said Eberhardt Schneider, an analyst at the Federal Institute for Eastern Research and International Studies in Cologne, West Germany.

During a trip last May to Romania, the Soviet leader went into detailed public explanations of his new policies of glasnost and perestroika, or restructuring, as if to set an example for party leader Nicolae Ceausescu. Romanian party officials, in the midst of their own campaign of austerity and repression, bristled in response.

"Ceausescu told Gorbachev very clearly in public that we are a people who have gone through many changes," Andrian Ionescu, general director of the official Romanian news agency Agerpress, said in Bucharest. "And we are used to doing things our way."

In East Berlin, even the use of the term "new way of thinking" -- coined by Gorbachev to describe the philosophy behind his reforms -- has been banned from the state-controlled media, according to official East German sources. "To accept it would mean questioning the basis on which the party has governed for the last four decades," said Schneider, who is a specialist in East German affairs. "They can't afford that."

East German leader Honecker, instead, has taken advantage of Moscow's loosened grip to further his own foreign policy objectives. Last month he succeeded in making a long-planned visit to West Germany, a trip apparently barred due to objections in the Kremlin as recently as two years ago.

As a result, a skyrocketing number of East German tourists now are allowed to visit West Germany. Last month it hit the record level of 1 million, double last year's figure.

So far, most of the progressive initiatives made by East Bloc leaders are in close accord with relaxations in Soviet policy. Honecker's trip to West Germany, for example, falls in the context of a general thaw in relations between Moscow and Bonn.

With Moscow's controls over its allies loosened, however, some leaders seem prepared to take positions that are at once more progressive than the Kremlin's, yet potentially threatening to Soviet rule.

In the wake of Honecker's trip, for instance, behind-the-scenes efforts to bring the two Germanys closer together apparently have been revived. Moscow has traditionally opposed such moves.

Honecker's visit already has prompted flourishing rumors that the Berlin Wall will be coming down soon and that Moscow is considering a plan to reunite the two countries.

In a West German newspaper interview two weeks ago, senior Bonn official Ottfried Hennig said a commission of Soviet officials has been established to study the possibilities of a confederation between the Germanys. The report, according to diplomatic sources in Moscow, originated with East German officials. Soviet officials have denied it.

The emerging economic and political disparities across Eastern Europe and the debates about limiting party influence also are potentially threatening to Moscow. Even in the early debate stages, discussions in Budapest and Warsaw of political reform movements that Moscow has opposed recently raise questions about how much glasnost the Soviet Union will tolerate in Eastern Europe.

Some western Sovietologists conclude that while Gorbachev has rejected the so-called Brezhnev Doctrine on paper, his own, more flexible policies toward Eastern Europe have yet to withstand the tests of time and political challenges. The Brezhnev Doctrine, depicted by western specialists as the guiding foreign policy of former Kremlin leader Leonid Brezhnev, established intractable Soviet hegemony over the socialist course charted by the communist-ruled countries of the world, including Eastern Europe.

Gorbachev publicly advocates toleration of different paths to socialism in Eastern Europe and elsewhere.

The extent to which Moscow allows East Bloc countries to pursue their own policies will say a great deal about Gorbachev's credibility on foreign policy.

The Soviet Union has nonetheless helped create a mood of anxiety in Central and Eastern Europe by leaving vague the answers to some fundamental questions: In the place of a rule by diktat, what kind of leadership would it offer allies? How would it react to the kinds of crises that occurred in Prague in 1968 and Poland in the early 1980s?

Although the 56-year-old Soviet leader appears unable or unwilling to herd along his reformist path such aging, conservative leaders as Romania's 69-year-old Ceausescu, East Germany's 74-year-old Honecker or 74-year-old Czechoslovak leader Gustav Husak, Gorbachev nevertheless has at his disposal three means of preserving order and unity within the bloc, according to western specialists.Contacts with younger leaders. Kremlinologists say one way that Gorbachev has tried to ensure intra-bloc harmony is by maintaining close ties with younger East European leaders who are gradually assuming leadership.

For example, Hungary's Karoly Grosz, 57, who flew to Moscow shortly after his election as prime minister last June, maintains close ties with the Kremlin. With Kadar heading toward retirement, Grosz is widely viewed as the heir-apparent.

Succession crises loom in Romania, Czechoslavkia and East Germany, however, where the governments either have purged most progressive figures or have stifled their emergence. Intra-bloc squabbles. Although Moscow has sought to mediate disputes among various countries in the Soviet Bloc in the past, such differences also can be used as a means of distracting local activists and controlling some domestic tensions, according to western diplomats.

The ongoing spat between Budapest and Bucharest over the treatment of ethnic Hungarians in Romania has become a subject of public debate in the wake of Gorbachev's campaign for glasnost, for example. The Kremlin leader reportedly raised the subject during talks last May in Bucharest, effectively highlighting the Kremlin's role as a mediator of disputes rather than as a dictator of solutions.

"At the same time," said one Bucharest-based western diplomat, "Moscow, Bucharest and Budapest are all able to use the issue as a lightning rod to distract restless Romanian and Hungarian publics from other domestic difficulties." Warsaw Pact forces. The most daunting and omnipotent sentry of the East Bloc is the Warsaw Pact defense alliance, with its army of a million Soviet and East European troops spread out from the East German-West German border across five of the six East Bloc countries. Only Romania is without Soviet troop presence.

Far more than the other safeguards against sudden activism in Eastern Europe, the troops are Moscow's most severe deterrent to crisis in the region. Without them, Moscow would be hard put to render its extraordinary psychological control over Eastern Europe, even if it deployed more conventional weaponry there.

Following the latest meeting of pact leaders, in East Berlin last May, however, significant cutbacks in the Soviet military presence in Eastern Europe are inevitable, according to some western specialists. The publication of the alliance's doctrine at the meeting, stressing the defensive nature of the pact's agenda, paved the way for a possible across-the-board cutback of Soviet troops from Eastern Europe within two years, western analysts say.

Asked whether Gorbachev's "new way of thinking" has altered Moscow's method of handling political crises in Eastern Europe, one senior Soviet specialist in East Bloc affairs declined to answer directly.

"I have noticed a significant evolution in the way crises were handled in Hungary in '56, Czechoslovakia in '68 and Poland in '80 and '81," said Leonid Jagodovski, deputy director of the Moscow-based Institute of World Social Systems. "As for how we would cope with another one, I just hope we don't have to."

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