East Germany polishes architectural treasures in Berlin

East Berlin is getting spiffed up for its 35th and 750th birthdays. The old Royal Playhouse of 19th-century Berlin's master architect, Karl Friedrich Schinkel, was reopened Oct. 1, 40 years after it was destroyed in World War II.

The Schinkel statues that were finally returned from West Berlin a few years ago stand proudly on what is now the Marx-Engels Bridge. The St. Nicholas Church; the old law courts, the Gerichtslaube; and the 18th-century Ephraim Palace will shortly be restored or rebuilt on the banks of the Spree.

''This will be a large open square, the way Berlin used to be,'' explained a gray-haired woman on the steps of the playhouse as she surveyed the burst of last-minute activity on the plaza below.

Under the watchful eyes of trumpeting angels riding a lion and a panther at the theater's grand entrance, a worker hammered cobblestones into place shortly before the opening. Nearby a worker in a hard hat riveted a lamp.

The building's inauguration as a concert hall began a week of celebrations of the 35th anniversary of the founding of the (East) German Democratic Republic.

On one side of the playhouse the French Cathedral is in the last stage of a restoration being carried out with official permission and money largely donated by West German Lutherans. It is to house the Huguenot museum honoring the French Protestants who so enriched Berlin after they fled religious persecution at home.

On the third side of the plaza trees still grow on the roof of the blackened ruin of the French Cathedral's twin, the German Cathedral. This second cathedral is to be restored by 1987, the 750th anniversary of the first documented mention of the city of Berlin.

Together all this facelifting is gradually giving back to Berlin some of its old neoclassical grandeur. The government is spending millions on the various projects, as it spent millions last year restoring Martin Luther's landmarks for the 500th anniversary of the great reformer's birth.

This follows through on a Socialist Unity (Communist) Party Politburo decision of two years ago to ''develop still more strongly'' the country's ''cultural inheritance.''

East Germany's embrace of this historical heritage is fairly new. After the war the architectural heart of the onetime capital of the German Reich went to the Soviet occupation zone that later became East Germany. This center included not only the Schinkel playhouse, but also the opera house, Humboldt University, the Rathaus, and the Brandenburg Gate (as well as Hitler's bunker).

In its zeal to establish a new socialist state free of its capitalist past, East Germany left numerous famous buildings in disrepair.

The remains of the old Schinkel Hohenzollern Palace were demolished, and a glass-box Palace of the Republic was erected in its place. A modern Alexanderplatz was built as a showcase to rival the commercial glitter of West Berlin.

A few years back East Germany began rediscovering German (and not just socialist) history, however, and this is now having a distinct architectural impact on the capital.

Frederick the Great and Gen. Gerhard Johann David von Scharnhorst were rehabilitated, and the statues of these Prussian heroes were reinstalled on the boulevard Unter den Linden.

The freshly cleaned Schinkel statues on the Marx-Engels Bridge at one end of Unter den Linden close to Schinkel's Old Museum began to give back to this avenue something of its 19th-century tone - though the ensemble is broken by the high-rise Foreign Ministry and Palace of the Republic.

Behind the Palace of the Republic and cater-corner to it another block of buildings will be restored. This is the Nicholas district, containing not only the still standing St. Nicholas Church, but also reconstructions of the old law courts and Ephraim Palace and burghers' houses. Apartment bulidings and boutiques are to be mixed in here.

The target date for this section is also the 1987 anniversary.