An ancient secret glimmers in the darkness of Mexico's National Museum of Anthropology. With its vast central courtyard, and its way of opening up to surrounding Chapultepec Park, this museum embraces the sense of scale and native surroundings of Aztec and Mayan civilizations. Its two-story horseshoe of exhibit halls provides massive framing for the splendors of ancient Mesoamerica (a region running roughly from present-day north-central Mexico to the northern reaches of Central America).
But the thing that moves you most about this place is more subtle than stone and scale. It is the fact that the Museum of Anthropology occupies the geographic and spiritual center of Mexico's longing to understand itself.
Enrique Florescano, director general of the National Institute of Anthropology and History, which oversees the country's regional and national museums, describes this longing as a ''yearning for a symbol of national identity . . . a new vision . . . an aesthetic built from the values of antiquity.''
This is the secret that makes itself gradually felt as you move through the ages in the museum's chronological and geographical structures. Mexico's obsession with finding a national identity is answered in part here among the Aztec monoliths and tiny expressive figurines of more ancient peoples. As if to underscore this connection, the museum houses a smaller panorama of life in contemporary Indian tribes in its upstairs spaces.
''We live integrated with the Indian life in Mexico,'' comments Mario Vasquez , director of the museum. ''We have everywhere the (heritage) of our ancestors.''
By way of illustration, Professor Vasquez, a gentle man with the majestic, spreading beard of an El Greco figure and the dark, quiet countenance of a Mexican Indian, pulls on his beard, saying, ''This belongs to the Spaniards.'' Then he yanks up his sleeve and, pointing to his skin color, adds, ''This belongs to the Indians.''
And the spirit of inquiry that led to the formation of this museum belongs to both. The old Mexican saying about an ancient Indian people puts it well:
In truth, the Toltecs were wise,
For they looked into their own hearts.
For the Mexican government, looking deeply into this country's heart has meant exploring the mirrors of ancient civilizations and pouring great sums of money into gathering and maintaining collections of ancient artifacts around the country.
None is more lavish or internationally acclaimed than the Museum of Anthropology, which incorporates state-of-the-art exhibition techniques with architectural genius and some of the richest archaeological treasure fields in the world.
The place's stock in trade is, after all, the endless stone riddles of Aztec sun gods; the minute clay castings of time-distant craftsmen who imparted a quizzical eloquence to their work to rival a Picasso or a Miro; the intelligent searching and planning that laid out cities complex and livable.
The museum houses collections of artifacts as primitive as 10,000 BC vertebrae fashioned into the head of a coyote, and as elaborate as AD 1500 postclassic headdresses and household objects. The exhibits move through these nearly 12,000 years of Mesoamerican civilizations chronologically, showing burial grounds, hunting scenes, the development of games and religious observances (often closely intertwined), and household implements, as well as the massive temple constructions and famed sun god monthly calendar.
Whatever else the successive waves of peoples that conquered and were conquered here possessed, they had the uncanny ability to communicate in stone and clay the very rudiments and aspirations of their lives.
A grimacing, contorted priest wearing a tiger skin from about 1000 BC tells a tale of hierarchal power and arrogance. ''She of the Jade Skirt,'' a Teotihuacan water goddess from about the time of Jesus, is a perfect, giant figure of domination and indifference; it stands more than nine feet tall and is an object inviting long contemplation. The god Xipe Totec, ''the flayed one,'' exemplifies how far craftsmen can go in overdecorating. The wonderful Olmec wrestler, from somewhere between 200 BC and AD 200, flexes himself in a purely Oriental stance that somehow blends muscularity and soft contours.
All of this is presented in the context of the land and how cultures grew up with this land . . . from the age of mammals through the primitive origins of man and the successive civilizations that have passed away on this soil.
The museum is well suited to the task of presenting both country and culture. We are not just dealing with display areas here, but the feeling of yawning distances in time and space. The Museum of Anthropology stretches across a span of time incredible for its complexity, pageantry, and savage history.
If you follow carefully the prescribed routes, and study the nuances in the artifacts, you will see a tale unfold of primitive expressiveness evolving into intelligent thought.
Several thousand years ago, men were making objects that mirrored in some way our own lives, because they were fashioned in the image of fear and longing and many of the elemental things we still deal with.
In one dark corner, there is a small black dog, full of wildness and antiquity. He sits in stone silence, once a pet of the gods and a household companion to some Aztec family.
There is no way to explain or describe the specific gravity with which he occupies his place in time. Or to tell how he speaks of the strange blend of tranquil domesticity and untamed wildness still at large in the Mexican countryside. Just as there is no better way to understand the people who made him than to go and look at their handiwork. Practical information
The museum is open from a.m. 9 to 7 p.m. Tuesday through Sunday. It costs 50 pesos (about 30 cents) on weekdays and Saturdays; Sundays and holidays, 25 pesos. Tours are available in English, French, German, and other languages. Special, slightly higher rates apply for museum tours.
The National Gallery of Art in Washington is currently showing ''Art of Aztec Mexico: Treasures of Tenochtitlan.'' Most of the pieces in this exhibit, which runs through April 1, are on loan from the Museum of Anthropology in Mexico City.