Communist East Germany, carved out of the rubble that was the Soviet one-third of a conquered and divided Third Reich, celebrates its 30th anniversary in massive celebrations here this weekend.

Its official birth as the German Democratic Republic -- coming just a few months after the Western allies gave birth to the Federal Republic of Germany in the western two-thirds of the country -- marked the beginning of the postwar alignment of power between the Western alliance and the Soviet Bloc that is still intact today, marked by the German dividing line.

Giving birth to two new Germanys in those days was like bearing a sullen and battered child that was already aged. Since then, both have grown and changed dramatically. Yet the communist state, to many in the West, remains a puzzle.

For the first two decades of the postwar era, East Germany, despite its establishment as a state within the Soviet Bloc, remained relatively isolated from much of the rest of the world. The rest of the world not only did not recognize East Germany it had little interest in it.

Then, after the 1970 treaty of normalization between West Germany and the Soviet Union, things happened fast. In 1971, the breakthrough in four-power negotiations on Berlin led quickly to a 1972 treaty between the two Germanys and, in 1973, to admission to the United Nations, a major prize sought by the East German government of Erich Honecker.

Today, East Germany is no longer isolated or shy. It calls itself one of the 10 leading industrial nations of the world. Its athletes dominate Olympic Games and other international events with the help of a government that saw this as a way to gain the long sought-after respect and recognition. Its troops and technicians are to be found in a dozen countries of Africa, advising revolutionary governments.

Yet, the German Democratic Republic remains a complicated place of extraordinary contrasts.

Without the aid of anything like the American Marshall Plan that helped rebuild West Germany, East Germany has managed an impressive rebuilding job on its own.

Massive housing projects have gone up throughout the country, city centers have been rebuilt. Television sets, dishwashers and private automobiles are the rule rather than the exception. There are no real slums or poverty of the kind found in U.S. cities.

The apartments, city centers, and consumer goods are relatively poor by Western standards, but the standard of living, despite shortages and frustrations, has been increased greatly in the past 20 years.

These achievements -- given an imposed Soviet ideology, economic system and not much help from Moscow -- are not minor ones and are a source of pride to most East Germans, even the malcontents.

Yet, it is a gray kind of prosperity here. East Germany is a humorless place, still rigid and somehow sad in the forced restraint of the full range of human emotion.

The reason is well known. Overwhelming the pride is the fact that, with the exception of retirees over 65 and a handful of other people, the 17 million East Germans are sealed in behind fortified borders and the Berlin Wall. They cannot get out.They cannot travel to the West, even for a visit.

Between 1949 and 1961, when the Wall went up, about 2.5 million East Germans fled west. The Wall stopped what not only was a humiliation to the government but a massive hemorrhage of the fledgling communist state's skilled manpower.

Today, despite big official youth parades, the dominant depressant among the most energetic and free-thinking youth appears to be their awareness that the state will not let them see what is beyond the Wall.

If the Wall came down tomorrow, undoubtedly many East Germans would leave. However, many would also stay, or come back after leaving, because of the pride in their country and because the West, with its competitiveness, its image of violence, racial tensions and materialism, does in fact scare a lot of East Germans raised in the totally controlled postwar state.

Ironically, East Germany today is probably more traditionally "German" than West Germany.

Although the Kremlin controls the East, and has 400,000 troops there, Soviet culture has made no impact whatsoever on East Germany, while American culture has dramatically and probably permanently changed West German society.

That same "German-ness" adds to the complexities of the East in other ways. The traditional German orderliness and obedience to authority is reflected in many ways here, especially in the total official devotion to the Kremlin on all things.

Yet each year, several thousand East Germans risk their lives in sometimes ingenious efforts to escape.

Furthermore, while a handful of dissident intellectuals in Czechoslovakia, Poland, Romania and other Soviet Bloc states capture headlines in the West, more than 100,000 people showed up at the West German liaison office in East Berlin in 1976 to seek emigration to the West under the Helsinski agreements. It was, perhaps, the most widespread act of civic courage in the East and caused some East Germans to wonder what would have been the effect of similar courage 40 years ago.

Culturally, East Germany is also becoming poorer as its international role widens, with more than two dozen leading writers, poets, musicians and film directors either fleeing from the East or being exiled within the past three years.

Today, the German Democratic Republic remains a paradox. Despite the show of strength on the streets Sunday, the country faces very severe economic, and possible energy, problems.

The steady economic growth of the early 1970s not only has leveled off, but it also has been at a plateau for a few years, leading to relative economic stagnation and general malaise. The 1978 economic growth was less than planned and this year's apparently is worse because the government, for the first time, refused to publish the semiannual national income figures.

Despite the slogans of dedication on the walls, the country, more than ever before, seems bothered by its very special problem. West German television can be received in about 80 percent of East Germany, making it harder here than it is elsewhere in the Soviet Bloc to spread the ideological message. New laws forbidding contact with Western reporters reflect the new insecurity.

Oddly enough, those contacts with East Germany that can be pursued seem somehow to be overlooked in the West. Despite its growing industrial strength, its important military role and its crucial location in the heart of Europe, very few people seem interested in East Germany.

Not many Western journalists visit here, except on special occasions, and numerous U.S. diplomats stationed here over the years complain privately that nobody in Washington, including the State Department, seems to care much about this place. The German Democratic Republic may be dull, but it is not unimportant.