There are three excellent reasons for including an exhibition of Piranesi prints in the opening of the National Gallery's East Building.

This year marks the 200th anniversary of Piranesi's death.

The East Building's masterful handling of space recalls some of Piranesi's soaring architectural fantasies.

And Andrew Robison, the National Gallery's curator of prints and drawings and a leading Piranesi specialist, has done exhaustive research on Piranesi's early work and a comprehensive catalogue will be published this fall.

This third reason permeates this exhibition.

"Giovanni Battista Piranesi: The Early Architectural Fantasies" gives the National Gallery an opportunity to demonstrate that its new East Building will be devoted to art historical scholarship as well as to artistic dazzle a la Dresden or hot-off-the-blow-torch up-to-dateness as represented by Anthony Caros scrap iron "Ledge Piece."

Giovanni Battista Piranesi was a Venetian-born archeologist, architect, engraver, decorator and designer who produced 1,300 engravings, most of them inspired by Roman ruins, which he sold to scholars, collectors and tourists. His prints were so popular that he often altered his old copperplates to print slightly different images and that additional prints from his plates continued to be made for over a century and a half after his death.

This is why you don't have to be a Croesus or a Mellon to buy a print made from an original Piranesi plate and why scholars have endless fun sorting out what is what in the confusing mass of altered, revised and reissued Piranesis.

Before he went to Rome to dig for and draw antique Roman ruins, Piranesi studied perspective and stage set design in Venice. And perspective and drama are what he brought to the infatuation with classic architecture and the fascination with ruins of his time. This fascination, in fact, became a mania that went so far that artificial Roman ruins were built on English country estates.

Piranesi's early fantasies, notably series of tombs, grottos, caves and prisons, border on the bizarre. Later ones strive for monumental gradeur, decipiting architectural crescendos of space and emotion. These visions inspired the Ecole des Beaux Arts and such buildings as Daniel Burnham's Union Station. They undoubtedly also informed Ieoh Ming Pei's East Building.

Although most of Piranesi's prints are sheer imagery, they are composed of architectural details and ornaments depicted with archeological accuracy.

Piranesi futhermore handled his burin and etching needle with exquisite skill. He often enlivened his architecture with lyrical vignettes of grazing cattle, human anecdotes and country idylls.

The National Gallery exhibition, however, does not set out to present Piranesi as the unique phenomenon in the history of art, but focuses instead on Piranesi as an art historical problem.

With admirable clarity it elucidates the master's technique, the scope and sources of his inspiration and the histroy of changes in his plates and the quality of his prints.

It is a model exhibition for scholars. But while the layman is told a little more than he may care to know, he is at the same time not told enough.