El Greco, whose paintings comprise the summer-long exhibition that opens tomorrow at the National Gallery of Art, has for good reason been one of the more fascinating, and passionately interpreted, of the Old Master painters. His was a rare, complex, ecstatic vision wedded to a stupendous talent.

The exhibition--"El Greco of Toledo"--is above all a rare opportunity. The 57 paintings in it represent about 20 percent of the great artist's lifework, the most ever assembled in a single place, and include a dozen or so of his best paintings. Besides that the show, keyed to recent scholarship, adds a lot of worthwhile information to the already formidable El Greco casebook.

The subtle, revisionist arguments advanced by the historians who put together both show and catalogue will be debated for years to come. At best they provide new insight into El Greco's relationship with Toledo, his adopted city in Spain; at worst they almost make the master painter look to be a scheming careerist and dreary pedant. His art, of course, will survive the debate.

El Greco's mature paintings are charged with a peculiar magic--the elegant, stately and yet incredibly active dance of his figures, their sometimes overwrought ecstasies, the wonderful (as in "full-of-wonder") flickering brushwork and flashing, irrational lights and shadows. For the last 25 years of his life, masterpiece after masterpiece issued from his hand with amazing assurance, originality . . . and regularity.

His life story is an improbable one, even among the often unpredictable lives of the painters. Born in Crete, trained as an icon painter in the Byzantine tradition, self-propelled on a mission to Italy to learn the great lessons of Renaissance art, he became--by some extraordinary chance--the foreigner who led Spanish painting to the first towering See related story, C13 k of its fabled "siglo de oro." Seemingly more Spanish than the Spanish, he nonetheless continued to sign his name in his native tongue throughout his long life (1514-1614). His real name was Domenicos Theotocopoulos.

The exhibition is admirably selected to demonstrate the amazing transformation that took place in El Greco's art after he settled in Toledo in the middle of his middle age.

None of his early, Cretan paintings are known, but their small size and Byzantine technique can be assumed from some of the first things he did after arriving in Venice. The first of several telling comparisons of identical subjects in the show pairs a tiny, tempera "Annunciation" he painted before 1570 and a larger, more accomplished and much more Italian version of the same theme created five or six years later, in Rome.

Clearly, this is a young painter ambitiously enlarging his skills and his sights. Still, there seems almost nothing in El Greco's Italian decade--certainly nothing in the first gallery of this exhibition--to predict what would happen to his art in Spain. It is almost too much to be able to walk from El Greco's Italy to El Greco's Spain simply by passing through a door: The flower blooms too suddenly.

But that is, more or less, what happened, in part because El Greco received no challenging commissions while in Italy. Seeking his fortune, he traveled to Spain in 1577, almost precisely at the midpoint in his life, and his art immediately, and mysteriously, took a promising new turn.

His earliest Spanish paintings clearly show the tendency of his art toward emotional, elongated figures set in ambiguous, shallow spaces, although they demonstrate even more tellingly his first mastery of the great lessons of Italian art. Michelangelo is present in the masterful, muscular figure of his painting of the martyred "St. Sebastian" (1577-78), but so too is the mature, original El Greco.

The turning point, in this show, comes in a central, high-ceilinged gallery devoted to huge, separate segments from one of his famous altarpieces--an "Annunciation," "Baptism of Christ" and "Pentecost" (a trio that makes up the most spectacular of the loans from the Prado Museum in Madrid). "If this room takes your breath away, it was meant to," said one of the scholars leading a tour the other day. Probably he was referring to his own intention and that of the other organizers, but one couldn't escape feeling that the artist intended it, too.

With the exception of the tremendous "Laocoon," owned by the National Gallery, and his views of Toledo, El Greco painted two kinds of pictures: religious images and portraits. Besides their other notable attributes, the portraits play an important role in the didactic scheme of this show by demonstrating El Greco's close relationship with the economic, social and religious elite of his adopted city.

The point is well made, and taken, that the sensitive patronage of these clergymen, lawyers and merchants gave him the ground he needed to nurture his extremely original vision. So, too, is the point that El Greco's style was dependent upon the theory and practice of 16th-century Italian Mannerism, and that his imagery was in fundamental agreement with the theory and practice of the Counter-Reformation in Catholic Spain.

These reasonable arguments, and others, are made by Jonathan Brown of New York University and the other scholars in their efforts to demythify El Greco's art. As revisionist historians often do, however, these go too far in their appointed direction. None of them quite comes to terms with the full richness, complexity and magic of his achievement.

The show is a triumph, though, and the catalogue a valuable document.

Organized by the Toledo (Ohio) Museum of Art and supported by grants from the American Express Foundation and the National Endowments of the Arts and the Humanities, the exhibition opened at the Prado last spring. After its summer at the East Building, which concludes Sept. 6, it will travel to Toledo and Dallas.