Christmas in the capital

Washington, D.C., is a buoyant town, a one-time swamp transformed into a center for government, architectural splendor, and historic events. It's not an intimate town, nor a New York or Tokyo, and it sits but a dark river's distance from the morass of suburbia. But it's our very own capital, a city where we can absorb a sense of nation and world - a vision of excellence, grandeur, and beauty as well.

Washington is a tourist town - for travelers and locals alike, and in December, Washington is a sightseer's glory. If you're fortunate and the city's struck by a full-fledged blizzard, you'll find Washington a sublime assemblage of great stone buildings, brass, and wrought iron against wedges of clean white snow. The glitter of wealth of individual and nation can be picturesque indeed, whether in the fruits of governmental extravagance or of posh domesticity.

Washington's singularity may be one of scale. It is a rare city this size that embraces institutions with the rank of the Smithsonian or the Library of Congress, as well as the beguiling intimacy and taste of a Dumbarton Oaks or Decatur House - small and yet superb monuments to history, architecture or Pre-Columbian art.

The Smithsonian Institution, of course, is Washington's showpiece, seven of its 13 components lining both sides of the National Mall and elucidating and demonstrating every subject from dinosaurs and space shuttles to Oriental art and contemporary sculpture. If you've come to Washington for holiday sightseeing , you should begin on the Mall and branch out later to the National Zoo, the Renwick Gallery or the Museum of African Art.

Everyone knows the routine of museums: long walks, an almost bewildering variety of things to see and absorb. And the extraordinary flavor and excellence of the Smithsonian museums guarantees you'll persist to the end. Nonetheless, the Smithsonian - with the help of the Smithsonian Associates - offers fascinating alternatives to just stopping and staring. If you plan ahead - and call ahead, too - you may attend everything from concerts and lectures to gift-wrapping workshops. You may brunch to the sounds of viols and harps, take a short course in ''recreating a Victorian Christmas'' or be transported for an evening to England and ''Christmas at Canterbury.''

Still at the Smithsonian, your child can watch ''The Elves and the Shoemaker'' in the Arts and Industries Building. Held in the Discovery Theater, it's a special production by Puppet House Players. On the day after Christmas, the Museum of American History begins a six-day revival of holiday traditions from Colonial times to the present: Christmas, Hanukkah and New Years. Dickens' ''A Christmas Carol'' will be performed; there will also be musicians and dancers. Food crafts, films, and fun.

On December 20 alone, for example, you may sample everything from Children's Radio Theatre, the Potomac English Handbell Ringers or Appalachian Art Films to Japanese Ukiyo-e Prints and the 20th Century Consort.

And with the Smithsonian, you've just begun to see Washington. To even the most jaded Washingtonian, the Mall is a magnificent place, the glowing monuments and Capitol building at night stirring even cynical hearts.

If you're wise, you'll abandon your car at your hotel or guesthouse and use the subway - METRO - or taxis. It's a Washington sport to tow cars these days, and your spirit of celebration will remain intact if your car remains where you left it. Besides, only on foot can you appreciate the spectacle of the Mall's open space, the cool sumptuousness of the National Gallery's East Building, the Air and Space Museum, the pristine Hirshhorn Museum and Sculpture Garden.

Diversity is Washington's Christmas bonus, and exercise is a good foil for more intellectual pleasures. The National Sculpture Garden and Ice Rink is right on museum row, a neat disk of ice set between the Natural History museum and the National Gallery of Art. You can rent skates there and enjoy it day or night.

Washington's diversity rescues your senses on other levels as well, for the sheer magnitude of the Smithsonian may make you yearn for simplicity. Washington abounds with more personal splendors. A few blocks from Dupont Circle is the Woodrow Wilson House, what Mrs. Wilson called ''an unpretentious, comfortable, dignified house . . .'' now owned and maintained by the National Trust for Historic Preservation.