BERLIN -- The hated Berlin Wall has come down, and unification of Germany is a fact. But ironically, a new wall is rising between Western Europe and the East, as millions of Easterners and Russians, desperate over deteriorating economic conditions, bang at Western doors trying to get in.

Hungarians, Poles, Yugoslavs, Romanians, Bulgarians and Czechs, for so long locked into the East bloc, fear that they are about to be locked out of the West: In post-Cold War Europe, a big divide is shaping up -- huge areas of great relative prosperity in the West side-by-side with areas of abject poverty in the East.

The same divide, of course, existed before. But during the Cold War, Easterners could look West only with envy, knowing that they could get no exit visas. Today, it's easier to leave Poland or Hungary than it is to get a permit to enter France or Germany.

Thus, warns David Anderson, director of the Aspen Institute of Berlin, a "Fortress Europe" is emerging in the West, designed not to exclude other nations' goods and services, but their people.

"Western Europe is on the edge of facing a migration of millions of human beings, perhaps beginning in three to four months, and officials won't talk about it. Their deep, secret hope is that if they don't talk about it, the problem will go away," Anderson says.

One estimate at an Aspen Institute conference here was that the 12 million emigrants now registered in Europe will double to around 25 million in this decade, and -- absent a stricter immigration policy -- zoom to a total of 50 million by the year 2000.

Taking it all together, the East-West division in Europe is now beginning to resemble the more traditional, if equally intractable, North-South division, says Daniel Hamilton of the Carnegie Endowment for International Peace.

Underlying the problem is the deterioration of economic prospects in Eastern Europe (far worse than anything imagined earlier this year) and a threatened breakup of the Soviet Union. The former Soviet satellite nations have been liberated only in a political sense: Neither democracy nor significant economic aid from the West has yet arrived in Eastern Europe.

West European officials estimate as many as 3 million Russians, facing starvation this winter, will try to get into Eastern Europe and thence into the countries of the European Community. European governments do not like having it stated so bluntly, but their official policy is to roll up the welcome carpet. The doors may not be fully closed, but for sure, they won't be left wide open.

When Mikhail Gorbachev loosened his hold on the satellites in 1989, the hope emerged in those countries that some of the enormous wealth of the West, so tantalizingly nearby, would trickle across the borders into Eastern Europe. But except for East Germany, it hasn't happened. With standards of living just as bad or even worse than they had been before, old hatreds and prejudices, including antisemitism, have risen to the surface.

Some Soviet Jews are even trying to emigrate to Germany. That in itself is a stunner. Bonn hasn't yet decided what to do about it: A quota limit is a possibility.

Western Europe's policy of exclusion applies not only to individual immigrants from impoverished Eastern European nations but to countries such as Turkey, Austria, Malta and Morocco that want to join their rich neighbors in the European Community. However, their bids to enter the community are being rejected by the politicians and the influential business-banking community, at least for now.

"Turkey," says Piet-Jochen Etzel, a member of the board of the Dresdner Bank in Frankfurt, "is not Europe." Etzel wants to help the poor countries, "but not at the expense of unification." He's content to see Europe proceed on what he calls "a two-tier level."

Exacerbating the problem is a likely flood of refugees into Western Europe from North Africa. The London Times cites a forthcoming EC study indicating that North Africa will account for 95 percent of the combined population growth of Europe and the Mediterranean over the next decade.

Long unguarded frontiers, such as Finland's with the Soviet Union and Italy's extensive coastline, coupled with the plan to abolish internal frontier checks within the EC, make illegal immigration difficult to track.

"Jack Kennedy used to say that rising tides lift all boats," Carnegie's Hamilton says. "But it doesn't help if all the boats are under water, and that's where the Eastern European countries are today." It won't be easy for Europe to survive with half its population enjoying a high standard of living, the other half scrounging for bread and housing.