A survey of Mexican art, in which 12,000 years and all major cultural and geographical areas are covered, is being shown at the Smithsonian's Museum of Natural History, after which you can step across the Mall to the Hirshhorn to concentrate on three great modern Mexican painters.

This means that you can give yourself a comprehensive course in considerably less time and space than you could if you were in Mexico. On the other hand, efficiency isn't everything, and there's no place on the Mall to stop for a Mexican beer.

No papers are required, but it is suggested that you pay attention to tracing pre-Columbian forms through the Spanish influenced periods so that you can be ready to see how they survive in the work of Orozco, Rivera and Siqueiros, who are known as Mexico's Three Biggies (Los Tres Grandes) of this century.

The two exhibits, form which some 200 significant Mexican works have been culled from national musuems and collections, was put together, according to the Olga Hammer, the curator, with the idea of tracing "the Mexican persona" as expressed in its art. Hammer the curator is no relation to collector Armand Hammer, whose foundation is sponsoring the exhibits to which a variety of Mexican museums, including its spectacular National Museums of Anthropology and History, have contributed.

The idea started with a Mexican exhibit in Spain, which had the theme of illustrating its Spanish influence. Olga Hammer is using some of the same objects to trace the opposite. Through what looks like typical Spanish religious painting, European academic and officcial styles, 19th-century portraiture, she insists on the survival of peculiarly Mexican characteristics as shown in the pre-Columbian works. "An acceptance of time," "calmness," "the absence of a need to show one emotion over another - but just to be," are some of these.

In the expressionless face of a wealthy Victorian lady, she sees not the vapid expression of English portraiture of the time, but the serenity of an enigmatic Olmec face. In the strength of a Rivera peasant, she sees the natural continuation of indigenous attitudes, rather than a conscious return to them.

However, this is only one thesis that can be extracted from it. The material is there.