ART AND SCIENCE are powerfully paired in two exhibitions at the National Academy of Sciences.

John Van Alstine, who builds massive sunworks with aesthetic genius and scientific exactness, shows through paintings, models and blueprints how his ideas become objects.

Painter Chuck Forsman uses the searching light and sinewy landforms of the American West to enchant us with the beauty of the landscape and to indict us for our stewardship of the land.

Van Alstine, one of this country's most popular and prolific sculptors, is living proof of the old saw that art is 10 percent inspiration and 90 percent perspiration. His giant solar calendars and super sundials require almost as much site research and engineering as an astronomical observatory, yet they fit into the landscape as though they had grown there.

The show escorts us through both the creative and industrial processes that culminated in works that grace the Supercomputer Research Center in Bowie and the campuses of St. Lawrence University in Canton, N.Y., and Austin College in Sherman, Tex. It's a subtle and penetrating reminder of the principle that good art is technically sound and good science is beautiful. However, those of us with limited engineering experience would benefit from considerably more explanatory text.

Forsman, whose palette perfectly captures the interplay between the West's searing light and sere landscape, uses honest deception to lure us into his land-use lessons. His scenes, so full of energy that they bulge and twist and overrun their frames, are stark and beautiful at first glance, then puzzling: What's wrong with this picture?

What's wrong becomes clearer the longer one looks. Reservoirs that drown canyons, subdivisions that carve away mountains, superfluous bridges, strip mines mauling mesas, buildings that impose upon the landscape when they could have complemented it.

But there's no off-putting preachiness in Forsman's sermons, just overwhelming beauty and uncomfortable truth.

JOHN VAN ALSTINE: DOCUMENTS and CHUCK FORSMAN: CONTENTIOUS TERRAIN -- Both through March 26 at the National Academy of Sciences, 2100 Constitution Ave. NW. 202/334-2436. Open 8 to 5 Monday through Friday. There is excellent wheelchair access to the Forsman paintings but none to the Van Alstine exhibit.