The first major exhibition of the paintings of El Greco, the 16th-century mannerist best known for his writhing forms and elongated figures, will come to the National Gallery of Art as next year's major summer show. The 80-item exhibition will open here in July 1982.

"He's got to be one of the best-known painters in the world," Nbational Gallery director J. Carter Brown said yesterday. "But his paintings are scattered so widely that for years it was assumed that gathering them up would be too difficult."

El Greco, "the Greek," whose real name was Domenikos Theotokopoulos, was born in Crete in 1541. Little is known about his early life, but he probably went to Venice in the 1560s where he fell under the influence of Titian and Tintoretto. He was in Italy at a time when the rigors and lucidities of the art of the High Renaissance had begun to loosen. By 1577 he had settled in Toldeo, where he remained until his death in 1614. It was there that he developed his highly original style with its intense religious mysticism and restless forms.

The show was conceived about two years ago by Roger Mandle of the Toledo (Ohio) Museum of Art. That town claims sister-city status with Toledo, Spain, where El Greco established his reputation through works painted for the sacristy of the cathedral.An announcement of the show was to have been made here next week by Spain's King Juan Carlos, who was scheduled to disclose the plans while standing before the National Gallery's "Laocoon" by El Greco, which has a view of Toledo init. But the political crisis in Spain postponed the visit of Juan Carlos and the announcement of the show, according to this week's Newsweek.

Mandle went to Madrid to discuss the project with the director of The Prado, which has the largest extant collection of El Grecos in the world. He then discussed the project with Brown and Bill Jordan of the Dallas Museum of Art. Last July all of the parties involved met at the National Gallery to finalize the project, and American Express agreed to underwrite the show at a cost pegged by Brown at "zillions of dollars." The show will open at The Prado next spring, travel to Washington and then go on to Dallas and Toledo.

"The theme of the show is the context of El Greco in Toledo, Spain," Brown said. "It was the capital of Spain then, and the show will explore the humanistic environment there during the period of the Counter-Reformation. Because The Prado is involved we're getting a lot of help in collecting works that are held by private European owners."

The National Gallery has five El Grecos in its collection. Some will be in the show, along with his "Agony in the Garden" which is held by the Toledo Museum of Art.

In conjunction with the exhibit, a major catalogue will be published containing essays by the creators of the show as well as scholars Richard Kagan of Johns Hopkins and Jonathan Brown of of New York University.