The closest major airport to the Thousand Islands region is Syracuse, N.Y. USAir currently offers flights from Washington at $98 round-trip, based on a 30-day advance purchase with travel on Tuesday, Wednesday or Saturday. The rest of the week the fare is $118. The drive north from the Syracuse airport on I-81 is less than two hours.

An auto trip from Washington is about 500 miles. I-81 north intersects with I-70 just west of Hagerstown, Md., and runs right up to the Thousand Islands Bridge. For a more scenic route when you get close to Lake Ontario, detour west to New York Rte. 3 at Port Ontario and continue north through the lakeshore towns, including tiny, historic Sackets Harbor, site of two War of 1812 battles. Continue north via Rte. 12E to Cape Vincent. WHERE TO STAY: The communities along the St. Lawrence shore, north and south, offer a wide choice of motels and motel-like resorts. On the south shore, two of the nicest, each with good water views, are the Edgewood Resort, (315) 482-9922, and the Pine Tree Point Resort, (315) 482-9911, both in Alexandria Bay. Summer rates for two at the Edgewood range from $58 (woods view) to $90 (water view) a night; at the Pine Tree Point, the range is $47 to $93.

*For information about renting an island or shoreline home, contact the Thousand Islands International Council (Box 400, Alexandria Bay, N.Y. 13607, 800-8-ISLAND) for a current listing of rental agents. Among them is Remar Rentals of Clayton, (315) 686-3579. Rates vary depending on the size of the home, but a private island cottage with five bedrooms is about $1,000 a week. To that you must add the cost of renting a power boat to get to the island, also available at Remar for about $420 a week. On a larger island with several cottages, a beach-front A-frame cottage is about $450 a week, plus boat rental. CAMPING: There are about 1,600 campsites at 13 New York state parks in the Thousand Islands. The charge is $7 a night. Reservations for a three-night minimum can be made through Ticketron outlets. Reservations for a week's minimum can be made at the regional park headquarters at Keewaydin State Park, (315) 482-2593. That is also the information number for the regional parks. About 50 percent of the campsites at each park are on the reservation list; the rest are allotted on a first-come, first-served basis. HOUSEBOATING: Remar Rentals in Clayton is also the principal houseboat agency on the U.S. shore. Prices range from $800 to $1,200 a week, depending on size, with sleeping accommodations for up to eight. Prior experience is not necessary, but these are large boats and not easy to maneuver, especially on a river with which you are unfamiliar. WHERE TO EAT: The dining room at the Pine Tree Point Resort has the best view of the river and good fare. A close runner-up for view and tops for food is the dining room of the Bonnie Castle Resort, also in Alexandria Bay. The region is full of inexpensive cafe's and restaurants serving the fresh catch from the river. INFORMATION: The Thousand Islands International Council, address and phone number above, serves both shores of the St. Lawrence.