Top equestrian teams from Canada, Great Britain, Switzerland and the United States will compete for trophies at the 1993 Washington International Horse Show, an eight-day event that opens next Sunday at 2:30 p.m. at the USAir Arena in Landover. Opening night is designated as Hunt Night, featuring a foxhound exhibition and competition by hunt teams simulating an actual hunting field. A medieval joust, Jack Russell terrier races, and a masters' class and amateur-owner jumper class are also on the evening's agenda. Highlights of the show are the events in which the world's top show-jumping teams compete. The first is "Super Jumps," the $10,000 Nations' Cup scheduled on Oct. 28. It is followed by the $10,000 Crown Royal International Gambler's Choice on Oct. 29; the $15,000 UST Puissance on Oct. 30 (competitors attempt to break the record of 7 feet, 7 1/2 inches set in 1983); and the $50,000 President's Cup Grand Prix on Oct. 31. Other attractions include the Western cutting horse finals, a pony division, draft horse hitches, hunter classes, the ladies' sidesaddle championships and shopping at over 100 boutiques. Evening performances begin at 7:30 p.m. during the week (except Wednesday at 7 p.m.) Saturday and Sunday shows are at 2 p.m. and 7 p.m. Ticket prices range from $6 general admission to $41 for a weekend box seat, with proceeds donated to various charities. For information, call (301) 840-0281 or (202) 432-SEAT. Tilghman Island Day If you're curious about the life of a Chesapeake Bay waterman, plan to attend Tilghman Island Day on Saturday. The island is home port to the skipjack fleet, the last remaining commercial sailing fleet in the United States. You can see them ** at sail in a noon race or take a skipjack cruise aboard the H.M. Krentz. At Dogwood Harbor, watermen will demonstrate clamming, crabbing, fishing and oystering tonging. You can take part in the waterman's games beginning at 10:30 a.m. and watch boat docking contests, workboat races and boat building. At Kronsberg Park, you'll find live entertainment, lots of food, an auction, and professional and amateur pickers and shuckers engaged in a crab-picking and an oyster-shucking contest. There's an arts and crafts show at Tilghman Elementary and a seafood feast at the firehouse. Festivities run from 10 a.m. to 5 p.m. A donation of $4 will be requested to benefit the Tilghman Volunteer Fire Company; free for children under 12. To reach the island, take U.S. 50 to Easton and Route 322 (Easton Parkway) to Route 33 through St. Michaels to Tilghman Island. Call (410) 822-4606. Skipjack Sail The third annual Skipjack Sail on Saturday is an effort to save Somerset County's declining skipjack fleet. Buses will depart Somers Cove Marina at 7:15 a.m. for Janes Island State Park and Wenona. The skipjacks will set sail from Wenona at 9 a.m. The first stop will be at Janes Island for a short break and briefing by a park ranger. The skipjacks will then sail around Crisfield to Somers Cove Marina, arriving there about 3 p.m. The trip fee of $22.50 includes bus fare. Deadline for reservations is Oct. 18. Call (410) 968-0925 or (800) 967-3474. Leaf-watching by train A fall excursion train is a good way to enjoy the fall color show. An Autumn Leaf Special is being offered on Saturday between Hagerstown and Gettysburg, Pa., by the Hagerstown Roundhouse Museum and the Hagerstown and Cumberland Valley chapters of the National Railway Historical Society. The five-hour trip passes over South and Jack's Mountains, an area bypassed by regular passenger service for more than 25 years. The route runs west of Gettysburg past the site where the first day of the Battle of Gettysburg occurred. The train departs Hagerstown at 8 a.m. and makes the return trip from Gettysburg at 4 p.m. There is also a shorter trip from Gettysburg to New Oxford, Pa., leaving Gettysburg at 11 a.m. and 1:30 p.m. The fare for the five-hour trip is $33 for adults; $30 for seniors; $20 for ages 4 to 12; free for ages 3 and under (who do not occupy a seat). The shorter trips costs $10 for adults and seniors; $5 for children. A discount will be available for those who take both trips. Call (301) 739-4665. Pumpkin festivals It's pumpkin time across the land, and next weekend finds pumpkin festivals popping up in a number of places. At the Landis Valley Museum near Lancaster, Pa., a fleet of wagons pulled by restored tractors will take visitors into the pumpkin patch Saturday and next Sunday. After visitors have selected their pumpkins, they take them to one of the large barns on the property to carve or paint them. The Southcentral Pennsylvania Storytellers Guild will be on hand with seasonal tales, and the Lancaster County Folk Music and Fiddlers Society will provide music. Everyone will receive a cookie to decorate, and visitors can sample old-fashioned pumpkin custard baked in the museum's wood-fired bake ovens. Hours are 11 a.m. to 5 p.m. Saturday; noon to 5 p.m. Sunday. Admission is $7 for adults; $6 for seniors; $5 for ages 6 to 17. The museum is just north of Lancaster on Route 272. Call (717) 569-0402. The Great Pumpkin The great pumpkin can be found at Old Bedford Village, the re-created pioneer village near Bedford, Pa., during the Great Pumpkin Festival Saturday and next Sunday from 9 a.m. to 5 p.m. This year's winner tips the scales at 609 pounds. Halloween activities include a costumed parade, "pin the tail on the black cat," a haystack full of surprises, pumpkin painting and carving, scarecrow making, and a pumpkin pie-eating contest. There will also be musical entertainment both days and magic shows at noon and 3:30 p.m. On Saturday children ages 6 to 12 who arrive in costume before 1 p.m. will be admitted free. Soon after there will be a costume parade with prizes awarded for the best costumes and children's games. Also on Saturday there will be apple butter making demonstrations, and the cider press will be in operation. Sunday's the day for the Great Pumpkin Contest, which is open to anyone who brings a pumpkin weighing 100 pounds or more to the village between 9 a.m. and noon. The weigh-in takes place at 3 p.m., and first prize is $100. Festival admission, including tours of the village, is $6.50 for adults; $4 for children ages 6 to 12. The village is on U.S. Business Route 220, one mile north of Bedford. Call (800) 622-8005.