'Tis the American Sampler Festival of Music, Dance and Culture noon to 7 Saturday with a bevy of 18-century entertainment: Dennis James on armonica (a musical instrument made of glass bowls) at noon, fiddlers Jim Morrison and Steve Hickman at 12:30, the chamber group Hesperus at 2, lacrosse stick-making demonstrations noon to 4 and free performances of "Quilting," a slide/music docudrama of ethnic experiences at 8 Saturday and 3 Sunday (reserve seats at 357-4176). From 4 to 7, shake an old-fashioned leg with the Court Dance Company of New York in contra and square dances. It's free throughout the Smithsonian's Museum of American History. 357-2700.

FESTIVALS, FOLKS Take your pick from the many festivals in or around town:

From a Cajun dance party, to a German brass band, to a 5,000-year-old Chinese lion dance, the Washington Folk Festival has it, noon to 10 Saturday and noon to 6 Sunday at Glen Echo Park. More than 500 musicians, dancers, craftspeople and storytellers representing the U.S. and 30 nations will perform on four stages, including folksingers Cathy Fink and Marcy Marxer, the Ukrainian Bandura Ensemble and a blues workshop featuring Barry Pearson, John Jackson and other locals. Admission is free. Call 281-2228.

The Northern Virginia Jewish Community Center brings turn-of-the-century New York City to Virginia with its "Lower East Side" festival noon to 6 Sunday at Chinquapin Park, 3210 King Street in Alexandria. There'll be Yiddish theater, klezmer bands and participatory Israeli dance, plus ethnic food sales. It's free. Call 323-0880.

Baltimore's international flavor can be sampled beginning this weekend and continuing most weekends through the summer with the Showcase of Nations Ethnic Festivals. The Lithuanians kick it off 11 to 6 this Saturday and Sunday at Festival Hall, Pratt and Sharpe streets, with crafts, music and plenty of food. It's $2, free for seniors and kids under 12. Call 301/837-INFO.

Have a fling, a highland fling at the Berrywine Plantation noon to 6 Saturday and Sunday. Throughout the day, you can kick up your heels to the skirl of bagpipes, watch sheepdog trials, check out craftspeople and sample Scottish food and drink. Admission is free; winetasting and tours of the grounds are $2 for adults and parking is an additional $2. It's on Glisans Mill Road, off Rte. 75 North in Frederick, and it benefits Children's Hospital. Call 301/663-8687.

A LOFTY VENTURE The third annual Kids Hot Air Balloon Rally takes things up, up and away for Kids, Inc., a local organization that grants wishes to terminally ill children. From dawn till dusk Saturday, there'll be tethered balloon rides ($2), music by the Redskins Band, clowns, pony rides, refreshments and an acrobatic ultra-light aircraft squadron performing above. There's also a race of 60 hot-air balloons. It's free, but parking is $3 at the Comsat properties, off I-270 in Clarksburg. Call 223-9746 or 659-5564.

THE RIVERFEST FLOWS ON Potomac Riverfest splashes into town this weekend with a boatload of entertainment. The Riverfest Parade starts things off at 11 Saturday at Constitution and Seventh NW and travels west to 17th. At 5 Saturday at Seventh and Water SW, it's the music of (among others) the S.O.S Band and the Cover Girls and, at 8, gospel singer Tramaine Hawkins. There's the funk of One Way at 6 Sunday, followed by Wynton Marsalis at 8:30. The Georgetown waterfront meanwhile is the site for the Mayor's Cup Crew Regatta with rowing teams from more than 20 schools competing and a hot-air balloon rally 10 to dusk. Fabulous fireworks by the famous Grucci family explode into action at 9:30 Sunday from barges anchored off Hains Point. And that's just the anticlimax: The festival continues next weekend at Anacostia Park, between the 11th Street and Pennsylvania Avenue bridges SE. Call 745-3737.

WOODEN IT BE NICE There'll be no hack jobs at the Northern Virginia Carver's Festival 11 to 4 Sunday. More than a score of carvers will show you how seriously they take their whittling with exhibitions, sales and demonstrations, including the carving of a 16-foot totem pole. It's at Colvin Run Mill Park on Leesburg Pike, five miles west of Tysons Corner. It's free. Call 941-7064.

SOMETHING NEW The U.S.S. Antietam, the most advanced war ship in the U.S. Navy, will be commissioned this weekend and, though the actual ceremony is not open to the public, you can take a tour of all 9,600 tons of the guided-missile cruiser between 12:30 and 4:30 Sunday. It's at the Dundalk Marine Terminal just outside Baltimore. Take I-95 north to I-695 east, cross Francis Scott Key Bridge and follow the signs. 301/837-INFO.

ARTSY CIRCLES Exercise both body and mind at the Dupont-Kalorama Museum Walk Saturday at seven locations: the Phillips Collection, Textile Museum, Woodrow Wilson House, Fondo del Sol, Columbia Historical Society, Anderson House and Barney's Studio House. Beside special exhibitions, events include sheep shearing at the Textile Museum, the videos "Godzilla Meets Mona Lisa" and "Painters Painting" at the Phillips and the dixieland sounds of the Fat Cats Festival Jazzers at the Anderson House. Everything is open noon to 6, except the Textile Museum and the Phillips, which open at 10. It's all free and within a 15-minute walk of Dupont Circle. Call 387-2151 for more information.

REST OF THE BEST The Francis Scott Key Monument rededication is 1:30 Sunday at Mount Olivet Cemetery, in Frederick, with concerts by the First Army Band and the 3d Infantry Fife & Drum Corps. Free. 301/663-8687 . . . The 23rd annual Safe Trucker Driving Contest, complete with dump trucks and cement mixers, is 9 to 5 Saturday on Third Street between Madison and Maryland NW in front of the Capitol. Free. Call 838-1885 . . . The Upperville Colt and Horse Show is 8 to 6 Friday and Saturday, with the finals at 2 Sunday at Grafton Farm between Upperville and Middleburg. It's $5, $1 for kids. 703/592-3858 . . . Goddard Space Center celebrates Greenbelt's 50th anniversary 10 to 5 Saturday with tours, exhibits and touchable moon rocks. Free. Call 286-8981.