THE clever covers of the "Circa 1492: Art in the Age of Exploration" catalog tell the show's story at a glance.The front cover superimposes an Italian painting from about 1494, a portrait of mathematician Fra Luca Pacioli, done in somber grays, greens, black, and maroon, on a colorful red, blue, and gold Aztec or Miztec ritual manuscript known as the Codex Cospi. The Codex cover picture is of the "Venus calendar" in which Venus spears the maize god who stands on a smoking field; next the water goddess is speared, resulting in a drought. The cool mathematician and the war of the spears represent two works of art from such diverse cultures, a paradoxical pairing in the age of exploration. One, the violent relic of a civilization that was destroyed by its conquerors, the other the precise geometric quiet of Jacopa de' Barbara's portrait of the Italian geometrician s urrounded by symbols of the science so important in the age of exploration. These two cover choices represent two-thirds of this three-part exhibition, divided into "Europe and the Mediterranean World," "The Americas," and "Toward Cathay." If you have that basic three-part map of the exhibit in your head, you will not go off course. "Toward Cathay" sails through art in Japan, Korea, China, and India circa 1492. It is symbolized by the back covers of the catalog, famous Chinese painter Shen Zhou's snow-shrouded Lofty Mount Lu done as a hanging scroll. Shen Zhou was celebrated as one of the four great masters of the Ming Dynasty. You may feel as though you've walked around the world by the time you're through seeing this vast, complex, demanding, and yes, exhausting exhibition. It's the biggest show the National Gallery, the cathedral of art blockbusters, has put on since the regal "The Treasure Houses of Britain." There are over 600 objects in the 30 galleries of the show in the East Building. It is a show which covers 30,000 square feet, filled with paintings, drawings, sculpture, tapestries, decorative art, maps, and scientific instruments. It required 50 scholars and dozens of other experts, and it involved lenders from 32 countries and the United States. But get one thing straight, as J. Carter Brown, the National Gallery's director puts it, this shouldn't be confused with history. "This is not a history show. If you look closely at the show, you see it is not a history show. This is not a history museum. We are putting together great works of art that have binding them together the fact that this species of ours made these things in a narrow band of time - at a moment of history that changed the world.... "The glory is to find them all assembled here, illustrating a theme of globalism and hinting that perhaps there is more to understand and appreciate and to know about other people's cultures, and the moment when this relationship can be said to have truly begun is 1492 or thereabouts. And so we call this exhibition 'Circa (or around) 1492, The Age of Exploration. This global show required three curators: managing curator Jay Levenson, who also curated the "Europe and the Mediterranean World" section as well as editing the show's catalog; Sherman Lee, University of North Carolina, Chapel Hill, who curated the "Toward Cathay" section, and Michael D. Coe, of Yale University, who curated "The Americas" section. Mr. Brown suggests that several of the objects here "could well be a one-object exhibition. You will immediately notice things like the Leonardo da Vinci portrait of Cecilia Gallerani ("Lady With an Ermine"). It is with the Mona Lisa and our own small portrait of Genevra de' Benci, one of only three [Da Vinci portraits of women] in the world. That single picture has never been to America before. "And Leonardo's drawing of the Vetruvian man ["Study of Human Proportion in the Manner of Vitruvius"] the most famous drawing in the world, arguably. And in China, great paintings by Shen Zhou, and from Japan great works by Sesshu Toyo will show there were incredible geniuses in that part of the world as well, at the time. "And then in our third section you will see, I hope, the degree of sophistication of native Americans in the hemisphere ... in the Aztec sculpture of Mexico ... such as one of my favorite works of art in any culture: the Xochipilli, the god of the spring, of dances, of games, of gambling, of love (I don't know if there's any difference between those two) and of the arts." But what each traveler to this humongous show takes away in memory is quixotic, depending on individual tastes. What I remember most and want to go back to are: a huge, star-studded Flemish tapestry (1450-1500) "The Movement of the Universe," in fiery orange, gold, and blue, in which a hovering angel turns the celestial sphere with a crank; Hieronymous Bosch's mystical "Temptation of Saint Anthony," a medieval dream/nightmare drenched in red; Da Vinci's exquisite lady with ermine, its perfection faintly blemished with a tiny diagonal crack in the upper-left corner; as well as his "Study for the Head of Leda" without the swan. Also appealing are: the merry bronze "Dancing Ganesa" with the typical elephant head, from 15th-century India; Michelangelo's powerful marble "Angel of the Stairs"; a 16th- or 17th-century orange and scarlet full-length feather cloak from the Tupinamba tribe of Brazil; the "Colossal Rattlesnake Head" in full fang, done by the Aztecs in basalt; the Inca Seven Sea Birds lined up like the Rockettes, in cut and hammered gold; Albrecht Durer's wonderful watercolors, "Lion" and "Lioness"; the haunting "White-R obed Kannon," attributed to Gakuo Zokyu of Japan; and the apricot and blue-green splendors of the "Portrait of the Hongzhi Emperor" from the 16th- to 17th-century Ming Dynasty. This vast, often fascinating show, packed with intellectual challenges, is not something you want to see all in one day. It is too big and arduous. Leaping from culture to culture and from science to art requires, as Brown says, intermissions like an opera. Be sure not to carry the massive, ambitious catalog into the show with you. It weighs 7 3/4 pounds and could be used as an anchor on this voyage. Dr. Sherman Lee, "Cathay" curator, says, "Sometimes I think it was an unwise decision to have an exhibition of this scale. The complexities of borrowing, and taking care of the various conservation requirements of the differing standards in different countries lead to unbelievable complexities, and there were many nights when I rued the day. "But having just walked through the whole exhibition, I must say I think it was worthwhile and I think it is indeed as an art exhibition should be, a wonderful visual experience."