THE NATIONAL Gallery and the Renwick Gallery are showing us what well may be the future of art, through some glass sparkly.

On Sunday, the National opens an exhibition of 121 glass masterpieces spanning the whole 3,500-year history of glassmaking. The Renwick show embraces monumental glassworks so contemporary that the dust of their creation has barely settled.

The National's show consists of the cream of the 25,000-piece collection of the Corning Museum of Glass. While the older objects inspire awe both for their beauty and for their antiquity, it is apparent from the collection's contemporary works that the best is yet to come.

As the art of glassmaking has grown into a science, the aesthetic possibilities of the medium have become so broad that just about the only remaining limitations are the imagination and skill of the artist. Where the old masters labored in frustration and uncertainty, the young masters revel in knowing that if they can conceive an object, they probably can create it.

In much of contemporary glasswork such freedom has led to anarchy, wild-formed glass whatnots -- whynots, rather -- seemingly made just because they can be. But emphatic reaffirmation that the art is in the idea comes from "Cityscape" (1981), by Jay Musler, arguably the outstanding object in the National's show. Although Musler, 42, is a former journeyman glassblower, he based the sculpture on an off-the-shelf industrial Pyrex bowl, and used oil paints on it to make sure some yahoo wouldn't pour punch in it. The work's bold conception and simple execution have the purity of genius.

Musler's piece also underscores the inanity of classifying even the most creative glassworking among the decorative rather than the fine arts, a distinction that this National Gallery show will help dispel.

Visitors will find themselves going a-tiptoe through this glittering glassland, fearful of the fragility of objects whose survival seems miraculous. Most are oxidized, chipped or otherwise marked by the passage of time, which only enhances their appeal.

As subtle as the superb lighting of the exhibit is the story it tells. From its beginnings in 18th Dynasty Egypt to the present, glassmaking has reflected the sweep and character of civilization. Here are the grandeur and decline of Egypt; the vigorous youth and gradual dissolution of Rome; the beacon of Islam shining steadily in a world gone dark; the exuberance of the Renaissance and the material mastery of the Industrial Revolution. All made more real and immediate by these goblets and lamps and bowls and vases and bravura pieces these peoples used and treasured.

By chance or choice, the ten dozen objects in the show amount to about one piece per human generation since the day some ancient Egyptian discovered that sand, ash and fire make something beautiful and brittle yet imperishable. Even should we incinerate the earth, explorers from another world would find the story of our Armageddon preserved in trinitite, the glass created at ground zero.

MASTERPIECES OF GLASS: A World History From the Corning Museum of Glass -- Sunday through March 17 in the East Building, National Gallery of Art. Open 10 to 5 daily and 11 to 6 Sundays. Metro: Archives.

GLASSWORKS: Site-Specific Installations -- Through Feb. 3 at the Renwick Gallery, 17th and Pennsylvania NW. Open 10 to 5:30 daily. Metro: Farragut West.