Old East Bloc Hostilities Surface as Threats to Infant Democracies : Europe: Poles fear Germans. Czechs are divided. Hungarians hold old grudges against Romanians. Reborn Europe faces severe growing pains.

Nationalism, ethnic identity and religion played crucial roles in shattering the communist domination of Eastern Europe. As the extraordinary forces of an extraordinary 1989, they were more powerful than the Moscow brand of Marxism-Leninism imposed four decades ago.

Identical forces rise in non-Russian republics of the Soviet Union and they erupt in communist Yugoslavia. The process seems to portend the end of a historical cycle begun with Russia’s 1917 Revolution.

Yet nationalism, ethnicity and religion may also create problems no less profound in post-communist Eastern Europe--antagonisms between countries and within them. Positive forces can become negative forces, undermining the effort to build democracies, reconstruct economies and assure reasonable social harmony.

The most difficult problems could involve relationships between Poland and the German Democratic Republic--East Germany.

In the immediate aftermath of World War II, Stalin annexed Poland’s easternmost territories, roughly one-third of the country, while awarding to Poland Germany’s eastern provinces up to the Oder and Neisse rivers. Millions of Germans were expelled in the process, losing homes and businesses, and being forced to flee to East or West Germany.

Long before the fall of communist regimes in Poland and East Germany this year, serious frictions had developed between the two governments despite mutual memberships in the Warsaw Pact and Comecon, the communist common market. Polish and East German warships fired at each other off the Baltic coast over fishing rights; East German organizations kept alive anti-Polish revanchism.

A territorial issue exploded only last month, with the collapse of the East German communist regime. The sudden possibility of German reunification reopened old sores on both sides of the Oder-Neisse border. Ethnic Germans who had stayed behind on the Polish side began organizing what Warsaw regarded as anti-Polish associations. The East German regime forbade Polish citizens to shop for goods on the German side of the frontier.

Earlier this month, Warsaw’s Gazeta Wyborcza, the new democratic newspaper with the largest circulation in Poland, charged that “explosions of anti-Polish phobia” among Germans were threatening the democratic order in Europe. The front-page editorial appeared just as the Polish government headed by Prime Minister Tadeusz Mazowiecki, a Solidarity leader, made clear that Poland would accept German reunification only after all Germans, East and West, formally recognized the Oder-Neisse line (as the Western Allies had done long ago).

Finally, West German Foreign Minister Hans-Dietrich Genscher felt the need to announce that “it is completely clear that Germans do not question the Polish western border--now or in the future.” But the issue remains. Chancellor Helmut Kohl made no such assurances to the Poles in his 10-point program for German unification and Genscher’s comment may have no impact on German public opinion, East or West.

The peril is not a new Balkanizing of sovereignties or frontiers but the threat of confrontations among former Soviet satellites and internal chaos. Throwbacks to oppression, if not neo-Fascism and anti-Semitism, could result.

Nationalistic or ethnic resentments were papered over during the decades of Soviet control, to present an image of communist unity to the outside world.

Problems in Czechoslovakia also date back to the 1940s. At the end of World War II, more than 2 million ethnic Germans were expelled from Czech lands by the Soviets. Those people are now agitating in Germany for what they regard as their right to return and regain their properties.

In Poland and Czechoslovakia, domestic public opinion angrily opposes such agitation, emphasizing that the Germans appear to forget that the existing state of affairs was a response to Hitler’s war and Nazi occupation.

To protect themselves from German demands, the Poles insist on a clear understanding with both Germanys on the inviolability of present borders “before it is too late,” as the Solidarity newspaper put it the other day.

Territorial problems also exist between Hungary, now moving toward parliamentary democracy, and Romania, still under a Stalin-style dictatorship, over Transylvania. Stalin had given almost half of the long-disputed Transylvanian territory to Romania as a reward, because her armies joined the Soviets in the closing days of the war after abandoning the Wehrmacht . Hungary did not switch sides. Now Budapest complains that ethnic Hungarians are ill-treated in Romanian Transylvania--and thousands try to flee.

Then come the internal problems, no less divisive, already developing in the nations barely out of communist control. In both Poland and Hungary, groups that until recently formed anti-communist opposition movements are now in power, especially in Warsaw where Mazowiecki is Eastern Europe’s first post-communist prime minister. Yet deep rivalries are already emerging within those groups.

New Polish and Hungarian political organizations are spawning right-wing factions that seem to be gaining strength. Renascent anti-Semitism is too often their common denominator, although Poland’s prewar Jewish population of 3 million has shrunk to about 12,000 as a result of the Holocaust. Hungary’s Jews number fewer than 85,000. In both countries, however, many key figures in the democratic leadership are of Jewish origin--as is East Germany’s latest Communist Party boss, Gregor Gysi--and the ancient prejudices boil to the surface.

In West Germany last week, the ultra-right Republican Party, headed by a former SS officer, announced plans to form a “sister” party in East Germany. In the Soviet Union, more than 70,000 Jews departed this year, a record exodus partly stimulated by relaxed emigration rules but also partly impelled by fear of nationalism and anti-Semitism within Russian, Ukrainian and Muslim republics.

Old tensions in Czechoslovakia, between Czechs and Slovaks, reappear. During the war, a Nazi puppet state was created in Slovakia, headed by Slovaks. Gustav Husak, who resigned last week as Czechoslovakia’s hard-line president, is a Slovak. As the new national leadership takes shape in Prague, one of the major issues will be balancing Czech and Slovak sensitivities to prevent a rekindling of inter-ethnic hatreds.

In Yugoslavia, still a communist state, the national unity enforced by Marshal Tito is crumbling. Since Tito’s death in 1980, ethnic and economic differences among the six republics and two autonomous regions that make up the Yugoslav federation have brought the nation to the brink of conflict and collapse. Serbia, the largest republic, is battling the more affluent republics of Croatia and Slovenia for political primacy. Croats and ethnic Albanians in the southeast have had physical confrontations. The economy is in shambles.

On the eve of the new decade, at the threshold of a free political and economic order, Europe’s infant democracies face severe growing pains.