Take a few sips of nostalgia at the Smithsonian's new Palm Court

There is a new, palm-fringed oasis for tourists in the humid desert of Washington summers. And the oasis tastes like ice cream. A turn-of-the-century Palm Court opened not long ago at the Smithsonian's Museum of American History. It offers visitors a vintage setting in which to kick their shoes off and have a few sips of nostalgia along with a strawberry soda.

You enter through the cast-iron, mahogany-colored facade of Brock's Stores, a 19th-century Philadelphia building. Directly in front of you is a reading lounge filled with Victorian white wicker chairs and couches, where weary visitors are already sprawled or curled up reading copies of Smithsonian Magazine or plotting the quickest route to the atom-smasher display. The furniture is comfortably cushioned in apricot, the floor thickly carpeted in rust plush. And there are enough potted parlor palms to do homage to the palm courts that graced so many hotels in the early 1900s and provided the ideal setting for musicales and tea dances.

Just beyond the palms are what are known in museum-ese as major artifacts: like a turn-of-the-century Horn & Hardart automat wall from Philadelphia. Its wooden walls are filled with old-fashioned automat food like huckleberry pie and American cheese on pumpernickel, all carefully encased in little glass-and-chrome squares with faded labels. (In the old days you put in your nickel and took out the pie, but today both prices and food are unreal.) Nearby are ornate old silver spigots for dispensing hot chocolate and other drinks.

Across the way is another slice of the past: a section of the original Stohlman's Confectionery shop, which at the beginning of the century was in the Georgetown section of the capital. ''This is a Museum artifact. Please do not lean on the counter,'' reads a sign on the golden-oak shop display. Behind the counter are dozens of apothecary jars filled with old-fashioned penny candy like dragees, rock candy, and cinnamon imperials. Beyond that the black-and-white hexagonal tile floor stretches toward a refreshment area where visitors can dish into sodas and sundaes amid period decor.

The man who put the Palm Court together is Michael Carrigan, assistant director of exhibitions and public space for the Smithsonian. ''There was no place for people to sit down and relax,'' he says. ''We wanted to provide a place where they could come and not just rest but get light refreshments, read a book.... If you're beating the pavement, it's a very tiring experience. If you stop and rest, you might stay a little longer, see more of the museum.''

Mr. Carrigan says the Palm Court addition, which covers 50,000 square feet, cost $150,000. But many items were donated, among them antique ceiling fans and a baby-grand player piano. At certain hours you can hear it whirring off priceless old music rolls, as the ''reproducing piano'' plays ''Rhapsody in Blue'' as performed by its composer, George Gershwin; Jerome Kern songs; or early jazz.

The skylit oasis replaced banks of escalators torn out for better use of the area. ''The space around the escalators had become a no man's land,'' says Mr. Carrigan. The museum has further plans for the Palm Court after Labor Day, when the tourist deluge dwindles: ''The menu would change to serve a light luncheon, afternoon coffee and tea, and salon music. We might have jazz or even tea dances. ... Already many people have remarked about the nostalgia of the room, '' he says.

We were talking over a little round table of tan marble and black cast iron in the eating area, which looks like a scene from the movie ''Ragtime.'' There are pressed tin ceilings, beaded and lacy wooden fretwork, and wicker-with-wooden ice cream parlor chairs. Waitresses are dressed in old-time uniforms: long navy cotton dresses with balloon sleeves, white ruffled aprons, and maroon ties. The ice cream is by Louis Sherry, a firm that dates back to the 19th century, and you have your choice of such exotica as ruby slipper strawberries on buttermilk biscuit with whipped cream ($1.50), and star-spangled banana split (everything but the rocket's red glare) for $3.95.

''We had a man come in who had owned his own ice cream parlor, like this one, and he looked around and said we'd set it up exactly right,'' said Mr. Carrigan with a certain curatorial pride. ''He said even the scoop buckets were in the right place for the soda jerks.''