THE political wonderland of post-communist Europe is about to produce another fantasticism: a German state in the heart of Russia. Germany and the Russian Republic agree that the autonomous Republic of the Volga Germans be recreated. In keeping with the surreal spirit of these times, the clock will be turned back to set it forward.The story begins in 1762 when Catherine the Great of Russia, born a German princess, needed settlers to colonize the land she was taking from the Turkish empire. None were available in her realm. The Russian peasants were serfs in bondage to the landowning nobility and not free to move. Catherine turned to Western Europe and especially to Germany for farmers and craftsmen. More than 25,000 accepted the invitation and the incentives that went with it - freedom of religion, no military service, tax concess ion, 70 acres of land, and local government. Over time, more followed and prospered. The largest colony, about the size of Estonia, lay in the Saratov area on the lower Volga river. It survived World War I and, under Lenin, was made an autonomous Soviet Socialist Republic. When Hitler invaded the Soviet Union in 1941, this Volga-German republic was dissolved. The people, including Germans, were deported to Siberia. After Stalin, repression was relaxed but German communities remained scattered. In 1989, the Supreme Soviet voted them - now numbering 2,250,000 - full political rehabilitation. But since the failure of the August coup all options are open. One is emigration. The German constitution gives all people of German ancestry the right to citizenship and a home in Germany. For decades, the Bonn government pleaded with Moscow to let its ethnic Germans leave. Only a trickle came out. Then, in 1990, nearly 150,000 went west and about as many are expected in 1991. Together with compatriots from Poland and other East European lands, more than 200,000 a year have moved. The German constitution also guarantees asylum to refugees from political persecution. They have received unusually generous support and services. These include painful anomalies like the 269 Soviet Jews in Berlin who fled Israel. Israel demands their return. Bonn would send them back, although forced repatriation is a sore point. But Berlin won't deport them. Non-Germans are coming by the hundreds of thousands, most of them as economic emigrants. Suddenly, polarity is reversed and the problem is differe nt. It is not to bring some people home and give others shelter, but to keep them both out. Germany has more than 5 million resident foreigners, 1 million of whom are asking for political asylum. With reunification last year, Germany inherited 200,000, mostly Vietnamese and Mozambicans, brought in as laborers by the former East German government. This should be no great problem for a country of 80 million. However, most European countries are not, like the United States, nations of immigrants. With their people aging, they fear demographic invasion. At a time of higher unemployment and shortage of housing, tempers are strained. Germans have been appalled to see violent racist outbursts against foreigners by skinheads and neo-Nazis. The ethnic Germans from the east - poor, alien, speaking broken German or none at all - feel lucky to be tolerated. If Bonn is agonizing over how legally to stem the flood of asylum seekers, it knows exactly what to do about ethnic Germans - give them the incentive to stay where they are. That means, above all, ensuring them a decent life of their own in their host country. Germany has used its considerable powers of persuasion and its economic clout to that end in agreements with all its Eastern neighbors. With Poland, Czechoslovakia, Hungary, and Romania, cultural and civic freedom, on a reciprocal basis, is the ans wer. In the USSR, the solution is seen in reestablishing the autonomous Volga-German Republic on roughly its original territory, gathering in all those still dispersed who choose to come. Bonn is pressing for quick action by the Russian authorities to build or restore villages, establish businesses, workshops, and farms, as well as to construct schools, hospitals, and German cultural centers. Germany will help. No cost estimate has been published, but it is likely to be a sizeable addition to the $35 billion or so in credits, loans, payments, and grants already earmarked for the Soviet Union to hasten the departure of Soviet troops from Germany and to keep the union on an even keel throug h its time of transition. Bringing this old drama to a happy end is not easy. Old-line communists, their minds on central control, opposed the idea. The KGB fomented demonstrations against it in Saratov. But the coup swept that away. Boris Yeltsin thinks differently. Still, Russian inhabitants of the area who remember the war and have misgivings about emigrants must be shown they will benefit. Bonn sees this restored symbiosis as a bridge of understanding. There will be some who say the ethnic Germans will be a fifth column. Hitler, helped by shortsighted allied policy after World War I, exploited them as a Trojan horse (though not in the USSR). Today, by some miracle of good sense, the democracy fostered in Germany by the same allies after World War II is solidly based and serves the idea of freedom.