The first major U.S. exhibition of Turkish antiquities in nearly 20 years will open in February 1987 at the National Gallery of Art. The announcement of the show, "The Age of Su leyman the Magnificent," came yesterday morning when Turkish Prime Minister Turgut Ozal toured the National Gallery's East Building. The exhibit required a change in Turkish law that has forbidden the loan of antiquities since the early 1970s.

The 200-object exhibition (150 from Istanbul's national museums, the rest from Europe and the United States) includes a mid-16th-century wooden throne inlaid with ivory, mother-of-pearl and tortoise shell; rugs; architectural tiles; rare illuminated and illustrated manuscripts (some showing Su leyman himself); inlaid woodwork; pottery; calligraphy; imperial caftans woven with silk and metallic threads; and ceremonial armor set with gold, jade and rubies.

"It's a sensual show," said its curator, Esin Atil, who is on loan to the National Gallery from the Smithsonian's Center of Asian Art. "I fell in love with the objects."

Su leyman, called in the West "the Magnificent," is known in Turkey as Kanuni (lawgiver). He reigned over the Ottoman Empire for 46 years (1520-1566). Su leyman was a poet as well as a patron of the arts.

A key part of the show will be a model and photographs of the 16th-century Su leymaniye, a complex of buildings, topped with 400 domes, constructed around a mosque. For many years, it was perhaps the largest, most magnificent building in the world, said William B. Macomber, president of the Metropolitan Museum of Art in New York, one of the three museums scheduled to exhibit the show.

Ozal admired the model of the Su leymaniye displayed in the great atrium of the East Building. "It builds to a crescendo," said James N. Wood, director of The Art Institute of Chicago, the other museum on the 1987-88 tour. The mosque's dome is 90 feet in diameter, sheltering the arcaded courtyard and 175-foot-high vaulted sanctuary.

Sinan, a great architect of the period, designed the building, constructed between 1550 and 1557. The complex includes 18 buildings arranged around the mosque, including four universities, a medical college, schools, a hospital, a cemetery and the mausoleums of Su leyman and his wife. Today the building still functions, though it is surrounded by fast-food establishments and other evidence of modernity.

J. Carter Brown, National Gallery director, escorted Ozal and his wife Semra through the East Building -- up the stairs and escalators, across the bridge and through great spaces brightened by the sun.

"The prime minister is a civil engineer," Brown explained. "He was especially interested in how we were able to hang the great Alexander Calder mobile in the atrium. He wanted to know what material it was made of and the logistics of its mounting. In our room of American contemporary painters, he said that he could see technological elements in the Robert Rauschenberg painting. The David Smith sculpture reminded him of microwave technology. My staff was concerned because we are installing the Festival of India exhibit and one hallway is under construction. But he was very interested in seeing a show put together."

Three of the principals putting together the Turkish exhibit have earlier ties to the country. Brown said his father, Nicholas Brown, had once headed the Byzantine Institute, which supported restoration in Turkey. The Metropolitan's Macomber is a former U.S. ambassador to Turkey. Curator Atil played a major role in efforts to change the Turkish law regarding antiquities. She is a native of Turkey.