For Folk Folks

Whether you're dying for a square dance or craving crafts, the 10th Annual Washington Folk Festival at Glen Echo Park is for you. More than 500 local artists offer traditional American and international entertainment, including music from 11-foot Swiss Alphorns, performances of Indonesian shadow puppets, African dancing and Appalachian clogging. You can learn how to dance flamenco or Louisiana Cajun styles in workshops. Or catch some storytelling, Irish music from Celtic Thunder, bluegrass with Grazzmatazz and Andean music from Alborado. It's all free and picnicking is recommended. Hours are Saturday from noon to 11 (square dancing begins at 8); Sunday, noon to 6. For more information, call 281-2228 or 492-6282. Down to the Waterline

Georgetowner Dena Sollins was walking along the C&O Canal one summer afternoon 10 years ago, when she got the notion that, by gosh, the canal ought to be alive with music. With a little help from Mobil, the idea became the annual Concerts on the Canal series. The series kicks off its 10th year this Sunday from 1:30 to 4:30 as the Charlie Byrd Trio and the Monumental Brass Quintet play on the canal at Foundry Mall between 30th and Thomas Jefferson streets in Georgetown. The free concerts, which run every other Sunday through September 7, will include music from the Smith Sisters, the Trinidad and Tobago Steel Band and Soda Bread. 862-1336 or 965-3100. Sly and in Person

Aside from his posters plugging "Cobra" at bus stops, Sylvester Stallone doesn't hang around in public too much. But Friday at 1 he'll make an in-the-flesh appearance on the steps of the Capitol for a torch-lighting ceremony kicking off the 18th Annual District of Columbia Special Olympics. Stallone, who'll be flanked by his wife Brigitte and Attorney General Edwin Meese III, will pass the torch to the first of 700 law officers who'll relay it 25 roundabout miles to Gallaudet College at 800 Florida Avenue NE (site of this weekend's Special Olympics for athletes with mental retardation). For details on the games, call 244-1910.

Stallone is also scheduled to throw out the first ball Saturday at the 6th Annual International All-Star Polo Benefit, where some of the world's finest players (from Argentina, Mexico, Pakistan and the United States) will be riding. Don't worry if you've never seen the game (it dates back 2,500 years), because an announcer will help explain everything during the match, which begins at 3 at the Potomac Polo Club. Gates open at 1 for tailgate picnics; there'll also be food for sale. Tickets, $5, are available at the gate, at River and Hughes roads near Poolesville. Proceeds benefit the Research Foundation of the Washington Hospital Center for Spinal Cord Injury. For more information, call 342-0465. Sports Specials

Spectators can get into the swing of outdoor sports with the following events.

*Go for the golf gusto at the 1986 Kemper Open at Bethesda's Congressional Country Club. In this PGA tournament, such pros as Greg Norman, John Mahaffey and Craig Stadler compete for a $90,000 first-place check. And with 345 acres of green, the country club has plenty of room for spectators. Second-round action gets under way Friday at 7:30 a.m.; the third round is Saturday at 9 a.m.; finals are Sunday at 9. (CBS begins live coverage on Saturday at 4:30; Sunday at 1 on Channel 9) Tickets, $17.50 and $25, are available at the gate, 8500 River Road. 320-4100.

*They're off! -- at Laurel Racetrack, where thoroughbred racing begins Sunday at 1:30. Racing is daily through July 11 (except Wednesdays and Fridays in June). Tickets, $3 to $5, are available at the racetrack (on U.S. 1 in Laurel). 725-0400.

*Some of the best amateur soccer teams from Virginia to Vermont compete in the United States Soccer Federation Region I Tournament of Men's and Women's Select Teams. The round-robin competition among 10 teams in each division is Saturday from 9 to 6. The finals begin Sunday at 2. The tournament's best male players will be selected to play in a national tournament, where they'll be under consideration for the 1988 U.S. Olympic squad. All the action is at the University of Maryland's Baltimore County campus in Catonsville (off I-95 south of Baltimore). 965-1549. The Ink Spot

The Museum of American History offers two free demonstrations on the art of printing. From 1 to 4 on the third floor west, Sylvan Kamm demonstrates printing in the 19th-century printshop, which is part of the exhibit Graphic Arts: First 100 Years. On the lower level, the 1986 Discover Graphics Printmaking Exhibition features a demonstration of how to print etchings from 2 to 5. The museum is at 14th Street and Constitution Avenue NW. 357-2700. Rest of the Best IN TOWN

Ultramarine: A Phantasmic Undersea Carnival of Day-Glo, a party celebrating the 10th anniversary of the Washington Project for the Arts, is Saturday night from 9 to 3 at the Yale Steam Laundry, 437 New York Avenue NW. There'll be live music from the Uptown Rhythm Kings and a deejay, dancing, a cash bar and a costume contest. Tickets, $10, are available at the door. 347-4813 . . . Friday at 6:30, the American Film Institute screens the Washington premiere of Troupers, a 1985 documentary about America's oldest political theater group, the San Francisco Mime Troupe. $4. 785-4601. IN MARYLAND

The Blacksmith's Guild of the Potomac offers Blacksmithing Days 1986, a free forging demonstration, Saturday and Sunday from 10 to 4 at the Roosevelt Center Mall in Greenbelt. 474-7763 . . . You can join in the Muscular Dystrophy Association's 10K Love Walk '86 along the C&O Canal in Great Falls Sunday beginning at 9 a.m. Entry fee is $5 the day of the event at the park entrance just off Falls Road. 823-1115 or 299-8989. IN VIRGINIA

The Herndon Festival '86 is Saturday from 10 to 9; Sunday from noon to 6. There'll be continuous entertainment on three stages, food, a business expo (Saturday only) and 146 craftsmen on the Town Hall Square. Free. 435-6868 . . . In addition to sheep dogs and craftsmen, there'll be live jazz and Scottish and bluegrass music at the 2nd Annual Oatlands Sheep Dog Trial and Country Art and Craft Fair. The event is Saturday and Sunday from 9 to 5 at Oatlands Plantation, six miles south of Leesburg on U.S. 15. Admission is $4; $3 for seniors and kids under 18. 703/777-3174.