As we cruise blithely into summer, reality spreads like an oil slick on the road. Searching for ways to use less gasoline, some people are getting bored with flying to Montreal for the weekend, while others are tired of walking around the corner to the library to read old magazines. What's left for weekend wanderers are buses, bikes, trains, boats, roller-skates and running shoes, or shorter jaunts in the car. Here are some shortcuts and close-to-home outings to avoid that nagging nightmare: 250 miles from nowhere, a mournful sound rises from the dashboard: "Eeeee..." YE OLDE PLANTATION BOATRIDE "I had rather be at Mount Vernon," George Washington once said. But how to get there without gasoline? The Mount Vernon Trail weaves 17 miles of bikepath one way starting at Memorial Bridge, but there are less exhausting ways to spend an afternoon.

The Diplomat, a 350-passenger cruise ship. leaves 6th and Water Streets SW twice daily, at 9:30 and 2. Roundtrip it's $5.50 for adults and $2.75 for children, plus admission to Mount Vernon, $3 for adults and $1 for children. A free shuttle bus to the pier leaves Gateway TourCenter, 4th and E Streets SW, two blocks from Metro's Federal Center station. WEAR HEALTH SHOES For old salts who want to reutrn to the sea, Annapolis is a mere 45 minutes away via Greyhound and Trailways ($7.35 round trip). Everything worth seeing is within walking distance of the bus station. Four blocks away, in the Old Treasury building on State Circle, is Historic Annapolis, Inc.: Guided tours of of the town run daily at 10, 1:30 and 3, at $2.50 for adults and $1 for students. But for nothing you can walk down to the city dock and see a new maritime exhibit. Once there, you can board the Harbor Queen and view the harbor from the inside out ($2.50). The boat leaves hourly, noon to 6. To explore the Naval Academy and pay homage at the crypt of John Paul Jones, find the visitor information center at Gate 1 on King George Street. Tours are $1 for adults and 50 cents for kids, and leave hourly, weekdays and Saturdays 10 to 3, and Sundays 11 to 4. SHOPPER'S NOTE Even when a person's hunger outdistances an auto's thirst, there may be ways to go to the store without a car. The truly decadent phone their order to Larimer's or Neam's. (They deliver.) Earthpeople wheel collapsible carts squeaking to the store and drag them home again. People who live near a Metro station have an alternative - Taking the subway to Eastern Market station and walking two blocks up Seventh street SE to the market for fresh produce, meats and atmosphere. Saturdays it's open from 6 to 7, weekdays, 7 to 6, closed Sundays and Mondays. COOKS" TOURS "Diet-busting daytrips" is what Heritage Tours calls their bus treks. They lead people who like food through the pleasant countryside into wineries, bakeries, catering kitchens, markets and farms.

Coming up are cooks' tours of the Amish Country (August 17, $35) and Washington (date and cost aren't known yet), a "Best of Baltimore" tour (September 6, $25) and a day in "Plantation Country" (September 26, $35).Call 362-4367. THE BLUE RIDGE LINE That old standby, Harper's Ferry by rail, begins to look even better. Amtrak's train departs Union Station at 10, arrives Harpers Ferry at 11:15, leaving time for wandering and lunch until the train leaves for home at 3:30. Roundtrip is $10.50, with savings on family plan on Saturdays.

Real rail fans will hop off the train at 11:05 to visit Brunswick, Maryland, and listen as trains bleat and bray in the yards of this railroad town. The heyday was the turn of the century, before steam went out, but the roundhouse is still there and the YMCA is always open. Brunswick # Museum, a repository for mementos of a train town that dug up arrowheads and sent its boys to war, is open weekends 1 to 5, at 40 West Potomac Street. MOO For farm sights, sounds and smells without going into the country, National Agricultural Research Center in Beltsville gives tours (about 2 1/2 hours) between 8 and 4:30 weekdays. Self-Gudided tours need a map, which is available at the visitors' center, building 186, on Powder Mill Road, reached via Edmonston Drive. Sights include a milking parlor, the conservatory (plant science), conservation (that old sludge magic), greenhouses, swine and beef cattle. With the map, you can self-guide around the research center on the weekend, but you won't see as much. (Call 344-2483.) Metro's R-2 bus passes less than a mile away. MERRY UNBLOSSOMS" The cherry trees, in their off season, are full of leaves, and touristry is down, which makes this a fine time to maneuver a paddleboat around the Tidal Basin. (One hour, two peiple, $2.45.) Since they rent boats through 8 in the evening, bring a picnic dinner and watch the sunset from the water. Who needs those faraway places, anyway? GOING ON CYCLES Sunday is coddle-the-cyclists' day in Greenbelt Park, where a 1 1/2-mile road is closed off for them around the picnic areas. The same goes for Rock Creek Park, where about two miles of Beach Drive NW are closed from 6 to 6. Pick it up at Broad Branch Road or Joyce Road.

Probably the world's skinniest park, the Washington and Old Dominion Trail is 100 feet wide and 1 1/2 miles long, where an old railroad abandoned its right-of-way. VEPCO powerlines are overhead, but bikers won't notice. To find it, from Key Bridge take U.S. 29-211 west eight miles to West Jefferson Street, turn right and go one block to the trail entrance.

For out-of-town touring, Frederick County has thoughtfully printed a booklet of scenic routes through covered bridges, past farms, streams and old homes. They'll mail "Cycling Tours" to you, if you send a check or money order for $2.60 to the Visitor Center, 19 East Church Street, Frederick 21701. CANAL BIKES Bikeless ones can borrow wheels from rent-and-ride concessions along or near the C&O: Fletcher's Boat House, Canal and Reservoir Roads ($1.50 an hour, $5 a day); Jack's Boat House, 3500 K Street NW ( $2 an hour, $6 a day); Swains Lock, out River Road and left on Swains Lock Road ($1.50 an hour, $4 a day); Big Wheel Bikes, 1034 33rd Street NW (depending on the bike, $1.50 or $2 an hour, $7 or $9 a day; three-hour minimum charge); Thompson Boat Center, Rock Creek Parkway and Virginia Avenue NW ($1.50 an hour).

Bikers and hikers hear the usual symphony of the C&O - birdcalls, runners' heavy breathing - but there are those free concerts as well, outside the Foundry Mall at 30th and Thomas Jefferson Streets NW every other Sunday at 1:30, July 29 through September 23. WHO WAS JUBAL EARLY? Or why? Named for a Confederate general, it's the only operating ferry on the Potomac, crossing at Whites Ferry in Maryland. Ride your bike out River Road to the ferry, pay a quarter for the crossing, and you're in Virginia a mere four miles from Leesburg. Leesburg is a nice place to visit (stop in the Loudoun Museum, 16 West Loudoun Street, for touring information). To Montgomery County residents, the ferry is a quick way to get there. Weather permitting, it shuttles from bank to bank from 6 in the morning until 11 at night. Pedestrians pay 25 cents and cars pay $1.50, one way. (Also, Whites Ferry store rents canoes and fishing boats from 8 to 8.Call 301/349-5200.) WHO CARES WHO'S ON FIRST? Why go all the way to Baltimore to see the Birds play ball when we've got our own professional team right here? The farm club for the Seattle Mariners, the Alexandria Mariners, the Alexandria Mariners, has a season of 140 games in 142 days. When games are home, the field is Four Mile Run Park, 3600 Commonwealth Avenue, Alexandria. It's the same game but at lower prices than major league - $2.50 for adults, $1.50 for 14 and under. The next home games are next Wednesday, Thursday and Friday the 27th. For a complete schedule, call 836-9397. IN THE AIR You may not be going places, but other people are. You can watch then taking off, an underbelly-view of the planes from National, at Gravelly Point on Roaches Run, neat GW parkway and Mount Vernon Trail. Sometimes FM radios near the airport can pick up pilots' talk with the control tower. Airport operations division says the chatter is somewhere in the middle of the dial. Listening in on a more sophisticated radio. try VHF 121.7. THE SCENIC JOG Anything viewed through a windshield is more real on foot, according to those who've tried it. Combining sightseeing and exercise, runners favor the C&O Canal towpath with its mileage markers, the Hains Point loop, the National Arboretum's trails and roads and the bike-path to Mount Vernon.

In local parks, exercise trails are springing up like an introduced species with no natural enemies. Rock Creek Park has a trail with stations for chin-ups and jumping jacks and so forth, just below Calvert Street NW. Since there's no place for parking, your car doesn't get to go. There's another along Beach Drive (a right turn from Connecticut Avenue on the way to Kensington) where your calisthenic antics may delight passing motorists. And still another trail in in Kenilworth Park, just off Kenilworth Avenue NE.

Here's a challenge. They've cleared a cross-country path at Lake Nee wood in Rock Creek Regional Park, and Montgomery College holds its meets there. It's a swath cut through open fields, up hills and along the lake. While the family runners are doing the 5 1/4 miles, others can ride the Needwood Queen, a mockup of a stern-wheeler, around the lake for 50 cents. Other sports can rent rowboats, canoes and pedalboats, shoot arrows at the archery range, picnic, fish or watch movies at Meadowside Nature Center nearby. Lake Needwood Park's hours are 10 to sundown. Go out Georgia Avenue to Route 28. Then take Route 115 and look for the signes to the park. FAST GETAWAYS When Hot Wheels run over Pop Rocks, do they become Pop Wheels? Actually, no. Pop Wheels are alternative transportation, sold by Hecht Company for $44. Now it's a leather-thonged clog; but pull a release button on the side and four red wheels drop down to roll you away. As a salesperson said, "People fall for them. I had a lady that rolled out the other day. It's comical: You ought to see them try them on in the aisles." CONCERT HOPPING Whenever there's a performance, there's a bus to Wolf Trap. American Tours picks up and drops off at the Hyatt Regency, Washington Hotel, the Mayflower, Howard Johnson's at 26th and Virginia, Hector's at Wisconsin and M, the Holiday Inns at 1900 Connecticut and at Tysons Corner, and at its own office, 519 Sixth Street NW, where parking is free. Round trip, $5. For reservations, call 393-1616. SUBURBIAPHILES Some people like to life decorating ideas from model homes. It's free advice. The place to go for this is Columbia, of course, where there are # usually at least 30 model homes and townhouses. Pick up a map and list of builders in the exhibit and information center, open daily 11 to 6, on the lake across from Columbia Mall. (Follow the signs to Town Center.)

On gasoline-less days, join the commuters and take the bus to Columbia, for strolling the mall or pedalboating a lake. Saturdays a bus leaves Trailways in downtown Washington at 7:15 a.m., and a reutrning one leaves Town Center at 5:55; $5.90 round-trip. (Call Eyre's Bus Service, 854-6600.) ANCHORS ACROSS THE BAY From the end of the city dock in Annapolis, the Annapolitan II runs to St. Michaels on the Eastern Shore at 10 every day but Monday. The three-hour stop in this old fishing village can be spent in the Chesapeake Bay Maritime Museum, Thomas Point Lighthouse or a woodworking shop where they build and repair skipjacks. The fare - $18 for adults and $9 for 12-and-unders - includes admission to the museum. (Call Chesapeake Marine Tours, 301/268-7600.)

For sailors shipping out of Baltimore, Port Welcome Tours floats a boat to Betterton Beach on the other side of the Bay, Tuesdays and Saturdays at 9, returning to Baltimore at about 6:30. Catch the boat in the inner harbor across from McCormick Co. It's $8 50 for adults, $4.25 for children. (Call 301/383-5706.) ON MASON NECK About 20 miles south of Washington, you can make a day of it on a peninsula on the Potomac. The morning can be spent at the late-1700s Gunston Hall Plantation, roaming its halls and gardens, and the afternoon in Pohick Bay Regional Park, throwing a picnic, swimming in a pool or pedal-boating. Take I-95 south, Lorton exit, and follow the signs. Gunston Hall is open daily from 9:30 to 5; it's $2 for adults and 50 cents for kids 6 through 15. The park is open all seasons, dawn to dusk. HARVEY S. LADEW AND YEW A man of independent means was Harvey S. Ladew. When he rode to that great foxhunt in the sky, he left posterity a bit of eccentricity - the Ladew Topiary Gardens in Monkton, north of Baltimore. On the lawn of his mansion, which is also open for tours, a fox perpetually outruns the hounds; suspended huntsmen and horses never quite jump a hurdle. In the whimsical sculpture garden he fashioned from yew (it grows at a fast clip) are lyrebirds, unicorns, seahorses, Churchill's top hat and a victory sign. His wit extended to the apple orchard, where he placed a statue of Adam and Eve. Ladew's uncle Barry Wall introduced the tuxedo. The place is about 65 miles from Washington. Take Exit 27 of I-695 (Baltimore beltway): On Maryland Route 146, it's 14 miles north of Towson. Hours for the house are 10 to 4 Monday through Saturday, noon to 4 Sunday; gardens only, 4 to 7. A special concert will be held among the hedges this Sunday at 6 when the Peabody Jazz Ensemble performs. It's $5 for adults and $1 for kids under 12. Admission to the gardens is $4; under 12, $1.50. (Call 401/557-9466.) TOOTHSOME SHARKS" TEETH More than a nuclear power plant, Calvert Cliffs rise to 120 feet above the Chesapeake Bay. Embedded there are fossils 15 million years old. These aren't for the taking, but in Calvert Cliffs State Park, fossil hunters can follow the Red Trail to ancient sharks' teeth that wash up on the beach. Good view of the cliffs, too.

For a closeup of the local paleontology, visit Calvert Marine Museum in nearby Solomons, a small fishing village. The museum also has exhibits on marine life in the Patupuxent River-Chesapeake Bay area, and artifacts of more recent maritime history, including the entire Drum Point lighthouse. And for a working lighthouse, there's Cove Point. The Coast Guard gives tours to small groups. Part of the property is beach area and good country to hunt more sharks' teeth and arrowheads. It's about 65 miles from Washington. Reach the Park and tmuseum by Maryland Route 4. To get to Cove Point, take Route 497 just south of Calvert Cliffs. PRESIDENTS" CHOICE Up Camp David way, two neighboring parks near Thurmont lure visitors with a range of activities. In Catoctin Mountain National Park, Round Meadow Craft Center highlights folkcrafts; nature walks leave the Visitor Center weekends at 1; a self-guided walk on the Blue Blazes Still Trail leads to a moonshine still; and Fridays and Saturdays close with a campfire at 9 in Owens Creek campground. (Call 301/271-7447.) Nearby Cunningham Falls State Park is special, of course, because of its 40-foot-long waterfall, but also because of Hunting Creek Lake. You can actually swim in it ( $2 for a car of three, 25 cents each for more people), or fish in it, or canoe on it. (Call 301/271-7574.) SKY-HIGH HIJINKS Maturing members of the backseat generation will sympathize, as the Flying Circus relives and recalls "the adventure and excitement of aviation's Golden Years" in Bealeton, Virginia, Sundays at 2:30. High points are biplaning, wingwalking, skydiving, hot-air ballooning and old-time comedy. It's $4 for adults, $2 for children 3 to 12, and free for 3 and under. Bring a picnic. (Call 703/439-8661.) CAPTION: Illustration, no caption