The National Gallery of Art finally has seen fit to exhibit American useful objects as art. It's about time.

"In Praise of America, 1650-1830" marks a recognition by the Gallery -- for years limited to collecting and exhibiting primarily easel art and sculpture -- that a sofa can be as much a work of art as a painting.

The National Gallery has shown furniture and useful objects before, but only those from foreign and ancient cultures, such as China, Egypt or Africa. Other art museums, including the Metropolitan Museum of Art in New York and the Boston Museum of Fine Arts, have been more generous in their appreciation of working objects. Both have large permanent collections of furniture, silver, china and metalwork from the United States as well as Europe and points east.

But for the National Gallery, the exhibition that opens to the public Sunday (after a preview invitational dinner last night) is a turning point.

Though primarily a furniture show, there are a number of handsome silver pieces, one or two of other metals, and some glass, china and pottery.

It is a collection of 83 masterpieces, all of them works of art -- perhaps more so than much of the so-called "fine art" of the period. And it is easy to understand why. In the 17th and 18th centuries, American society was developing. New homes and sometimes fine mansions couldn't be quickly furnished from abroad since everything came on slow boats from China and Europe. The settlers had brought little with them from across the waters, so they had a great need for chairs to sit on, cupboards to hold their treasures, silver to brew their tea.

A trained craftsman in England was well-advised to immigrate to the American colonies. In cities from Boston to Charleston, a fine wood craftsman would be a man of importance, and soon a man of means.

As this show reveals, most of the ideas they brought with them were from the great furniture pattern books of the times, the published drawings of designers such as Thomas Chippendale and Thomas Sheraton. Most of all, they brought with them great mastery of technique -- probably the greatest skill at working wood that has been known in modern times. Even the country pieces are of a remarkable standard.

Wendy Cooper, the show's competent curator (borrowed from the Boston Museum) presents the objects chronologically, from the relatively simple early pieces to the wild exuberance of the Empire furnishings, from the new land to the established Republic.

At the beginning is a Great Chair from 1660-1665, probably made in Boston. Square and masterful, it has its original Russian leather covering, stuffing and brass tacks, remarkably preserved. "The leather seems to have been scored to release the natural oils," Cooper said, "and perhaps this is why it has lasted so long."

A 1758 Newport chair shows how far comfort design had progressed in 100 years. It has a tall back to cradle the head and soft arms to rest upon. The chair has its original flamestick needlework upholstery on the front and sides, and on the back a needlework picture of hounds chasing deer in a wild paradise. It is the only piece of furniture in the show to be set in a lucite case: "Wouldn't we all love to touch that needlework?" said Cooper.

A slant-front desk (1771 from Chester or Lancaster County, Pa.) is remarkable for its light wood inlay on walnut. On its slant front, the date 1771 -- a wedding? an anniversary? -- is inlaid, along with two stars, a crown encompassing two birds and a name "Reese," obviously of a later date by an inferior craftsman.

Cooper said "i'm sure we will be criticized, but I thought we had to take the slant top off and display it above so you could see all the fascinating cubbyholes and such inside." The drawers as well have an elaborate border. And the brasses -- personally polished by Cooper -- are worth the trip.

A chest on chest (1790-95 from New Hampshire) is of white pine and tiger maple, a good example of the early craftsman's ability to match wood grain. One of the rarest pieces is the only desk/bookcase to boast nine carved shells. "There are five or six that have six shells," said Cooper. "But this is the only one I know that has nine." Made of mahogany with white pine and chestnut, it probably was built in Newport, 1760-1785, where John Goddard (the likely maker) and John Townsend brought the block-and-shell motif to a great art.

Of the handsome silver pieces, the 1705-10 Boston Monteith by John Coney is perhaps the most interesting. A Monteith was a bowl used to rinse wine glasses between courses. Wine glasses were hung from the scalloped top. The top was detachable, so the lower part could be used as a punch bowl.

By far the most sophisticated, not to say decadent, objects are the Empire pieces, gathered in the final gallery of the show. One sofa (New York, 1805-1815) is much like the one in the White House's red room. This one has wonderful dolphins, stained green, and two eagles, rearing up their heads and flapping their wings on either side.

A girandole mirror (1805-1815), lent by Edward Vason Jones, who has acted as consultant to the White House and the Department of State collections, is perhaps the most magnificent piece in the room, with its sea horses, leaves, cross quiver, bow, candle arms and chains of balls -- all elaborately gessoed and gilded.

Pointing out that not all good things were made above the Mason-Dixon line is the handsome 1790-1810 Georgia (possibly Athens) mahogany sideboard. The magnificent serpentine front is beautifully proportioned.

Washington's own important collectors, Mr. and Mrs. Joseph H. Hennage, have lent a high chest of drawers, Connecticut, 1750-1790.

Gaillard F. Ravenel and Mark A. Leithauser of the Gallery's design department have worked with Cooper in displaying each object so its particular beauty can best be admired, whether a shapely leg or an elaborate top. The only trouble they had in judging the heights of the platforms was that Cooper is 5 feet 1, and the men considerably taller.

All concerned should be congratulated for mounting each object with a plain and undistracting background, unlike the overly busy design (done out of house) used for the Thomas Jefferson Show in 1976.

The only period installation is a room at the beginning of the show done in the manner of the great 1929 Girl Scout Loan Exhibition, the culmination of that period's "craze," as Cooper puts it, for Americana. It was during these years that the major museum collections were made of American arts and the Williamsburg restoration began.

The National Gallery show marks the 50th anniversary of that exhibition. In the years since, much has been learned about early craftsmen and their homes, but there is much more to know. Then, the scholars were largely rich collectors and authors. Today, many scholars carry on the research. Cooper's book "In Praise of America: American Decorative Arts, 1650-1830" (Knopf) is a valuable addition.

What we have here is art, as good as any of your old master oils. And when you get tired of looking at a claw and ball footed chair, you can sit on it.