It is now official: East Germany is sending 700 objects and pictures worth more than $80 million for the exhibit that will open the East Building of the National Gallery of Art in June.

The formal announcement of the loan show was made at a ceremony yesterday attended by businessmen, Communists, bureaucrats and curators, whose presence indicated that art now can bypass the boundaries between the public and the private, conflicting idologies and the Berlin Wall.

The show, which will survey the history of art collecting, is called "The Splendor of Dresden: Five Centuries of Art Collecting, an Exhibition from the German Democratic Republic."

The Electors of Saxony, who began collecting treasures centuries before there were such things as museums, bought - or took as booty - Rembrandts, Durers, suits of armor, captured Turkish jewelled swords, the largest set of rose-cut diamonds that has ever been assembled, as well as Meissen porcelains, ivory and gold. One striking object to be shown is an almost life-size figure carrying a tray of enormous uncut emeralds. This exhibit is the largest that the East German government has ever sent abroad.

Mounting it in Washington, New York and San Francisco will cost considerably more than $1 million, of which $750,000 is a grant from IBM. Taxpayers will contribute $350,000 through the Arts and Humanities Endowments. The Robert Wood Johnson Jr. Charitable Trust has also contributed $350,000.

Art exhibits of this sort, whose costs are shared by governments, big businesses and private individuals, are no longer rare in Washington. It has been learned, for instance that "Treasures of Mexico From the National Museums," the two-museum show that will open here this month at the Smithsonian Institution's Hirshorn and Natural History Museums, is being underwritten by the charitable foundation of Armand Hammer, oilman and art collector.

Foundations and big businesses also have supported international loan shows from the Peoples Republic of China, Egypt and the U.S.S.R. The Gallery's China show was partially funded with a $200,000 grant from IBM. Exxon and the Johnson Trust helped pay for the exhibit of King Tut's Egyptian treasures, and Hammer, in the past, has underwritten local shows of state-owned Russian art.

The Dresden show will survey not the history of German politics, but the history of German taste, though, of course, the two are not entirely unconnected. The Gallery's designers will install the ark works in groupings that evoke their Dresden installations. One section of the show, for instance, will evoke the "Kunstkammer," or Cabinet of Wonders, assembled by the Dukes of Saxony in the late Middle Ages.

A second section, given to the Armory, will display noble weapons. Dresden's "Grunes Gewolbe," or "Green Vaults," with their baroque mirrored walls, also will be recreated as a setting for 130 pieces of diamonds, silver and gold. In the section called "Court Festivities in Dresden under Augustus the Strong," two jousting knights, dressed, as are their horses, in full knights, dressed, as are their horses, in full suits of armor, will be among the exhibits on display.

Johann Joachim Winckelmann, the 18th-century art historian who helped fire the Germans with enthusiasm for ancient Greece and Rome, was employed by the Dresden court. The German Expressionist painters who, in 1905-1913 called themselves "Die Brucke," also worked in Dresden, and their contributions, too, will be reflected in the show.

Although the City of Dresden was largely destroyed by Allied bombers during World War II, many of its treasures had been removed for safety and escaped destruction. "Phoenix-like, these witnesses to the staying power of Western civilization re-emerged in reconstructed settings following the war," said Gallery director Carter Brown. The Dresden exhibition will visit New York's Metropolitan Museum of Art and San Francisco's Palace of the Legion of Honor following its four-month stay, from June 1 to Labor Day, at the National Gallery of Art.