AS I ROLLED along the C&O Canal towpath one recent Sunday morning, my oncoming traffic consisted of a herd of deer that refused to stop for me. Pedaling around Greenbelt Lake another weekend afternoon, I paused to notice a solitary swan paddling by.

Along several designated bike routes in Northern Virginia, historical markers remind me that I'm cruising the same routes that American Revolution and Civil War armies traversed. Through Rock Creek Park, or the Northwest Branch or around Lake Accotink, I can navigate bends protected from the hot sun and secluded from civilization by lush greenery.

The Washington area is blessed with a wide variety of off-road bike paths where cyclists don't have to compete with cars for the roadway, so you can get your exercise enjoying different scenery each weekend during the summer. Biking is the best way to get away from it all and enjoy much of the area's natural beauty and some of its historical sights and other recreational facilities. Or you can just bike for its exercise value. Sling your bike on the back (or top) of your car with a bike carrier and you can get to all the trails in a short drive.

The following trails offer different types of rides and scenery. The more well-known paths get a lot of use on the most pleasant weekends, so consider some of the others to avoid crowds. You can ride 40 or 80 miles a day round trip on some of the longer routes, or just a few miles on some of the shorter ones. Most bike paths follow streams or encircle lakes and allow an opportunity to commune with all sorts of flora and fauna. Unless otherwise noted, most are paved or relatively smooth and flat.

On hot days, try the shaded stream valley routes, where trees block out the sun and the water and lower elevation offer respite from the heat. During a heat wave the temperature can be 10 to 15 degrees cooler in the valleys than it is above. Or bring a bathing suit and cool off in public swimming pools along some of the suburban parkway routes.

Of course, you can ride any of these routes in the reverse direction of that suggested below. So get your act in gear and roll on! THE MAJOR ROUTES

ROCK CREEK PARK --

The route starts where Rock Creek meets the Potomac River, at the foot of Georgetown in the shadow of the Watergate Hotel, and winds about 23 miles north. Watch out the first mile or so -- the trail is narrow and hugs the parkway perilously close. Exercise care again at the exercise course another mile or so up the trail -- after you go up one of a few steep hills you encounter, you must cross the parkway without a traffic light or stop sign. Be careful going down the hill on the other side as the trail is narrow. Just after that is a blind curve and another hill and possibly oncoming bike or pedestrian traffic. Shortly thereafter, you ride past the National Zoo, then the restored Pierce Mill and Art Barn -- both worth visits. The trail continues along Beach Drive, closed to autos on weekends. At Military Road, notice an open field in the middle of forest. It's Military Field, cleared as a training ground for Union soldiers during the Civil War. Continue along Beach Drive, which eventually curves west.

If you want to start back, turn left at Pinehurst Parkway, left at Greenvale Street, left once again on Western Avenue and back to an alternate bike trail which will take you along the western edge of the park back down to the main trail. But if you go on, note that around the next bend lies Candy Cane City, a playground with water, restrooms and portable toilets. The return trail is narrower and not as well-paved as the main one (nor as heavily used). South of Military Road, you'll hit some hills (which you can avoid by taking Military Road back east to the main trail). But if you stay on the western route, you can stop at the Nature Center. If you elect not to turn around, you can go about 13 miles to Lake Needwood in Rockville, where you can rent a boat or hike around the lake. Most of the trail is shaded, so the route is great on hot, humid days. You should bring some food, since Rock Creek Park includes no concession stands except at Lake Needwood. If you don't feel like biking back, turn left at Needwood Road (at the north end of the lake) and left again at Redland Road. It's only a few blocks to the Shady Grove Metro station.

CHESAPEAKE & OHIO CANAL TOWPATH --

This route starts at the same place as the Rock Creek trail and winds 184 miles along the Potomac, so don't plan on making it in a day. Start out on the Rock Creek trail, then turn left almost immediately at the wooden sign announcing the start of the C&O Canal. The trail may be full of pedestrians as you go through Georgetown, making riding impractical for a few blocks. Notice the historical buildings along the trail -- many were built along with the canal in the middle of the 18th century. At the far end of Georgetown (34th Street) be sure to cross the bridge from the north side of the canal to the south side. Otherwise, you'll hit a dead end. A few miles up, you can pause for refreshments or rent a canoe at Fletcher's Boat House.

As you go further up, the variety of plant and animal life you're likely to encounter gets richer -- as do the views of the Potomac rapids. Look for everything from turtles to deer, snakes and woodchucks. About 10 miles up the canal, you have a choice of carrying your bike over some rocks, or crossing a bridge and riding a rough stone trail on the east side of the canal (probably better to carry it). At Great Falls Tavern, you can stop for refreshments, go for a ride on a mule-drawn barge ride designed to show what life was like when the canal operated, and see the visitors center where you can learn about canal history. Two miles further, you can pause once again for refreshments at Swains Lock. You can keep going north until the canal ends in Cumberland, Md., but the trail gets rougher the further up you go.

You can also start your trip at several other places along the way, including Fletcher's Boat House (Canal and Reservoir roads NW) and Swains Lock (Swains Lock Road off River Road in Potomac). Bike rentals are available at both locations. You're better off taking a rugged mountain bike on this often bumpy dirt trail.

MOUNT VERNON TRAIL --

This trail allows you to follow the Potomac River downstream about 20 miles from the city named after George Washington past his farm and home. Though it's not well-marked, the trail begins on the south side of Key Bridge, two blocks north of the Rosslyn Metro station. It offers lovely views of the Potomac and takes you through Old Town Alexandria, where you can pause for lunch or just about anything else. It also takes you through Dyke March on a wooden boardwalk, and Fort Hunt, a suitable picnic ground. Watch carefully for high-speed traffic where the bike path crosses the road at Arlington Memorial Bridge and again at National Airport. Be ready for some steep hills the last mile or so before the plantation. Parts of the trail are too narrow for the traffic load, but since widening it would damage the riverbank ecology, cyclists must use caution.

The trail officially ends at Mount Vernon plantation, which has a snack bar and, for a fee, tours of Washington's house and estate. You can continue biking a few more miles on a paved trail, which crosses Mount Vernon Memorial Highway a few times. The National Park Service reports that peak use hours are between 8 and 11 a.m. and 2 and 5 p.m., so an off-hours trip can avoid cycle traffic. Most of the trail isn't shaded.

WASHINGTON & OLD DOMINION RAILROAD --

Like the C&O Canal, this trail offers a seemingly endless ride (45 miles one way) through nature and history from Alexandria to Purcellville. But unlike the C&O, it's paved for smooth pedaling. Much of the trail is out in the sun, so it's best to try it when it's not so hot. Along the converted railroad line, which opened in 1859, you can see several old train stations and hundreds of varieties of wildflowers, in addition to rabbits, snakes, deer and other animals crossing the path.

Suburban development around the 100-foot-wide park is pushing the wildlife further and further out, but it also provides for several community centers, bike shops and restaurants along the way. The trail officially begins west of Shirley Highway, near the intersection of Shirlington Drive and Four Mile Run Drive in Arlington. But you can easily access the path from several Metro stations to the west, including East Falls Church, West Falls Church and Dunn Loring. Don't try to get there from the Vienna Metro stop -- it's much easier from Dunn Loring, one stop east. Just bike a few blocks north on Gallows Road.

Civil War sites you'll pass in Vienna include a plaque at Park Street, which notes the first tactical use of a railroad in war, and the Freeman House on Church Street, where a skirmish was fought. The house, used as a hospital during the war, is now a general store with tours offered Sunday afternoons. Later, you'll pass through Sunset Hills in Reston, once the biggest farm in Virginia. The pond is filled with waterfowl and the ranger station is in a post office that was built in 1887 and later used as a train station. Keep going through a mix of natural habitat, historic Herndon and recent housing and manufacturing plants. But remember you'll have to pedal back.OTHER SCENIC HAULS

ALEXANDRIA LOOP --

This round trip of the perimeter of Alexandria on designated bike routes and paths covers about 15 miles and includes a few digressions you may want to make. Start at the Braddock Road Metro stop, head through the underpass under the train tracks and cycle west along the marked Braddock Road bike route. From this point, you'll go up the steepest hill on the trip soon after you start, when you have the most energy.

Notice the Civil War cannon as you pass Russell Road. Consider a one-mile scenic side round trip by turning left on Timberbranch Parkway and circling past some fine homes. Consider another 3/4-mile side trip through Fort Ward Park, a couple of miles from the starting point, where you can see the Civil War exhibits at Fort Ward Museum, open Saturdays 9 to 5, Sundays noon to 5. Then it's back to Braddock Road, downhill and underneath Shirley Highway to N. Beauregard Street. If you need bike repairs or food, turn right on Beauregard to a shopping area at King Street. Otherwise, continue straight, uphill along Campus Drive East through the Alexandria campus of Northern Virginia Community College. At the top of the hill, turn around and notice the view of downtown Washington. Continue southwest along Dawes Avenue past Seminary Road, left at Steven Street and right at Fillmore Avenue until the trail enters the woods.

From here on out, you're in parkland most of the way back. Don't be scared off by segments of the trail that aren't paved -- the road soon gets better. If you take a diversion left up a walking trail and through a parking lot you can visit the Dora Kelley Nature Center in the William Ramsay School (closed Sundays). The bike trail continues along Holmes Run past the 200-year-old willow oak designated by the city as the Bicentennial Tree. At Duke Street you can refresh yourself at an ice cream parlor or any of the other food shops. Shortly thereafter, the trail passes Cameron Run Regional Park, where you can cool off in the giant wave pool and water slides, or take a few swings at the batting cage. The trail continues east along Eisenhower Avenue. If you've had enough, board a Metro train at the Eisenhower Avenue station. Or follow the bike route signs through the Wilkes Street Tunnel to the Mount Vernon Trail. Head north through Old Town and west at Pendleton Street to get back where you started.

FOUR MILE RUN --

This trail follows a stream from the Potomac to Falls Church in a combination of shade and sun, and is about 12 miles one way. You may even get wet on the low bridges spanning the water. The unmarked trail entrance lies on the Mount Vernon Trail at National Airport's southern tip, where Four Mile Run meets the Potomac, and takes you immediately along the creek through an underpass. Go west to Glebe Road, following the marked bike route as it turns right and continues along the road. An overpass takes you safely over Shirley Highway to the Shirlington Village shopping center, where you can pause for ice cream or other refreshments. Use care crossing Arlington Mill Drive, as there is no traffic light.

Continue along the south side of the creek. If you turn left and take a side trip up a hill in Glencarlyn Park, you can stop at the Long Branch Nature Center. When the trail splits, stay on the south side; eventually the trail connects with the City of Falls Church Bike Trail. Follow the signs for a winding tour of this suburb's residential neighborhoods, downtown and parks.

The route eventually comes to a T-intersection with the W&OD Trail. Turn left and you can continue indefinitely on the W&OD Trail. Turn right and you'll come to the East Falls Church Metro Station two miles away. The W&OD Trail is north of and parallel to (sometimes merging with) the Four Mile Run trail. You'll soon come to a fork. Turn right and you can continue back to Shirlington, where you cross Four Mile Run Drive and take the trail you started on back to the airport. (The north side trail exposes you to more sun than the valley route.) If you turn left at the fork, you can continue 4.2 miles to the Rosslyn Metro station along the Custis Trail. This route parallels I-66, and involves a lot of ups and downs and very little shade.

ARLINGTON BOULEVARD TRAIL --

The boulevard, also known as Route 50, serves as the boundary between north and south Arlington. It also includes bike lanes along both sides, though often narrow and in the sun. You'll encounter few hills as you travel west on one side, east on the other, traveling from one end of the county to the other. The trail is about 16 miles round-trip, not counting side trips along adjacent bike trails you may want to take.

Get off the Metro at Arlington National Cemetery. If you don't mind a hilly ride, you can bike on a designated route through the cemetery, then through Fort Myer for about two miles. Otherwise, take the designated bike route west briefly from the subway stop and take the bike trail down a loop, then north along Jefferson Davis Highway. Pass the Netherlands Carillon and Iwo Jima Memorial. Follow the bike route signs north briefly on N. Meade Street (cross the highway very carefully). Turn left at the bike path on Fairfax Drive, which takes you to Arlington Boulevard. A side trail along Lubber Run offers a respite from the sun and civilization.

The main bike route stops at the Fairfax County line. If you continue a mile or so, you can find plenty of food at Seven Corners.

Return along the south side of Arlington Boulevard until you get to Washington Boulevard. Follow the bike route south along Washington Boulevard past the south side of the cemetery, past the Pentagon and then back to the Arlington Cemetery Metro stop.

TOURIST WASHINGTON --

Now that part of Ohio Drive is closed off each Saturday and Sunday at 3 p.m., you can cycle by most of the Mall's tourist attractions (about 15 miles) without too much competition from autos. Start anywhere along the Mall between the Capitol and Lincoln Memorial. East of the Washington Monument, it's best to ride along Madison and Jefferson drives to avoid rough surfaces, Frisbees and tourist throngs. West of the monument, several paved bike lanes take you past the Reflecting Pool, Constitution Gardens pond, Vietnam Veterans Memorial and up to the Lincoln Memorial. Head south through East and West Potomac parks around Hains Point on Ohio Drive or the bike route, then back to the Lincoln Memorial and Tidal Basin. Turn right through an underpass and the trail takes you along the Maine Avenue waterfront, past Washington's seafood market, a row of seafood restaurants and boat harbors. Retrace your trail and ride along the Tidal Basin.

From the west end of the Mall, you can cross either the Arlington Memorial Bridge or Theodore Roosevelt Bridge and hook up with several bike trails on the other side of the Potomac. Note: Decide whether you want to travel north or south before crossing the Arlington Memorial Bridge. You can cross on either side, but parkway traffic on the Virginia side of the river makes it very hard to cross the road.

BETHESDA/POTOMAC LOOP --

Visit Great Falls on a smoother trail than the C&O Canal towpath and cycle past some of the region's magnificent estates on this round trip of about 25 miles. Start at the Little Falls Trail at Bradley Boulevard and Glenbrook Road just southwest of downtown Bethesda. The trail takes you to MacArthur Boulevard. Turn right on MacArthur and head up the boulevard on the adjacent paved bike trail. Be careful as the trail crosses the road several times, but enjoy the Potomac to your left and bluffs to your right. You can stop at Glen Echo Park, where you'll see a former amusement park turned into an arts center. Potters and other artisans are often at work in huts at the park. Next door to the park is the Clara Barton House. Across the street is a small shopping mall where you can buy refreshments.

Between Glen Echo and Great Falls on MacArthur Boulevard you go over a one-lane bridge with timed stoplights at either end. Since cyclists must use a narrow sidewalk shared with pedestrians, you should walk your bike.

The trail is quite flat until you get to the foot of the Great Falls Recreation Area. Then it's a steep climb to Great Falls Park entrance. If you turn left, you can go down the other side of the same hill that took you into the park and can enjoy the views, nature trails and barge rides on the C&O. From the entrance, the bike trail turns northwest along Falls Road to River Road, where food is available at several shopping centers. The trail goes north along River Road about a mile before it dead-ends at Chapel Road. Turn around and it takes you down to Clewerwall Drive, where it dead-ends again. To return to where you started, turn back and head right on Bradley Boulevard (Route 191).

SLIGO CREEK/WHEATON REGIONAL PARK --

About eight shaded miles along a stream take you to a park offering a variety of recreation. The off-road trail begins in Silver Spring at the intersection of Piney Branch Road and Sligo Creek Parkway. Several parking lots off the parkway provide easy access. (Or you can start in the middle from the Silver Spring Metro Station. Follow the bike route signs at the north end of the Metro complex to Sligo Creek Park. Don't get lost at Fenton Street, where it's not clearly signed. Go left past the parking lot on Fenton, then continue north on Ellsworth Drive.)

After you cross University Boulevard, a spur takes you to Kemp Mill Shopping Center where you can buy food. When you reach Wheaton Regional Park under a mile away, a trail takes you through several wooded loops where it's easy to get lost and go around in circles. Once you get out, there are refreshment stands, a miniature train, hiking trails, a nature center, a farm animal zoo, and a greenhouse and plant exhibits at Brookside Gardens.

NORTHWEST BRANCH PARK --

This five-mile, well-shaded trail takes you through one of the few remaining refuges for wildlife in western Prince George's and lower Montgomery counties. The trail starts at Ager Road in Hyattsville, south of where it meets East-West Highway. You can leave your car in the park's lot and head north. Not quite two miles up, at Lane Manor, you can stop for a swim in the public pool, or take a brief side trip through a parking lot and over a few footbridges to adjacent University Hills Park, where you can dismount and walk around the bird pond. Back on the main trail, you will find pizza and sandwiches where the trail crosses University Boulevard. Or you can test your physical condition on the fitness course.

A tunnel takes you under Riggs Road to the Adelphi Mill, built in 1792. Then the trail gets into wilder country, so watch for birds and lizards. Because of the steep, rugged terrain further north, the bike trail stops just south of the Beltway. But you can hike further north through the wilderness.

If you start the trail from the north, head west on Oakview Drive from New Hampshire Avenue, just south of the Beltway. But be prepared to walk your bike down a long, steep dirt and gravel incline to get to the valley.

GREENBELT LAKE/NORTHEAST BRANCH --

For a trip of about 15 miles back and forth, start in Buddy Attick Park off Crescent Road in Greenbelt. Circle Greenbelt Lake, where you may glimpse a swan. Follow the bike route signs south of the lake to Greenbelt Road. Turn right and follow Greenbelt Road, preferably along the north sidewalk. Past Kenilworth Avenue, cross to the south sidewalk and turn south to the bike trail past 57th Avenue. The trail takes you through Paint Branch Stream Valley Park and past the College Park Airport. Where the bike trail ends, continue along Tanglewood Drive. Pavement eventually gives out to a dirt trail suitable for mountain bikes, but not for standard models.

After making your way back to the starting point at Buddy Attick Park, you can cool off in the public pool or hit balls in the batting cage.

C0LUMBIA TOUR --

The planned community of Columbia includes paved trails and residential streets that will take you around several lakes and parks. To get there, drive up Route 29 to Route 32 east, then turn north on Broken Land Parkway. Park at Lake Elkhorn. Several paved paths will take you to Town Center, where you can get fast food or dine at one of the outdoor cafes. North of Town Center, bike along West Running Brook Parkway and turn left on Ten Mills Road into Centennial Park. A three-mile trail around a lake involves a few hills and some sun but is well worth the view. Concessions and boat rentals are available.

HENSON CREEK --

This 13-mile round trip rolls along a stream. From Branch Avenue south of the Beltway, head east on Allentown Road, turn right on Brinkley Road, then right on Temple Hill Road. Park at Henson Creek Neighborhood Park and take a few paces north to the bike trail beginning. The trail goes to Oxon Hill Road but is often hard to find. When crossing busy intersections or parking lots, you have to look 100 feet or so down the road to find it. East of Tucker Road the trail is hidden behind a parking lot.

PAINT BRANCH/MARTIN LUTHER KING SPECIAL PARK --

About five miles of trail along a shaded stream and around a fishing pond are found in this western Silver Spring route. Best southern access is from Jackson Road, east of New Hampshire Avenue. The trail's northern end connects with more than 10 miles of bike lanes along Fairland Road, Old Columbia Pike and Briggs Chaney Road.

LAKE ACCOTINK --

About nine miles of park roadway and trail around the lake and to the north are suitable for mountain bikes, but not for most other vehicles. The best entrance is from the south on Highland Street, off Backlick Road, south of the Beltway in Springfield. TRAIL GUIDES

THE WASHINGTON AREA BICYCLIST

Association offers a series of maps and books outlining trails in the area. For more information, write WABA, 1015 31st St. NW, Third Floor, Washington, DC 20007. Call 944-8567.

FREE MAPS

of the Rock Creek, C&O Canal and Mount Vernon trails are available from the National Park Service, National Capital Region, Division of Public Information, 1100 Ohio Dr. SW, Washington, DC 20242. Call 619-7222.

A WASHINGTON & OLD DOMINION

trail guide costs $4.50 from the Northern Virginia Regional Park Authority, 5400 Ox Rd., Fairfax Station, VA 22039. Call 352-5900.

ALEXANDRIA ROUTES

are outlined in a Recreational Facilities & Bike Trails map available for $2 ($1 for Alexandria residents) from the City of Alexandria, 1108 Jefferson St., Alexandria, VA 22314. Call 838-4343.

ARLINGTON COUNTY

has 79 miles of on- and off-road routes and offers some of the richest biking opportunities in the Washington area. For free maps and other suggested rides, call the parks department at 358-3681.

MONTGOMERY COUNTY PARK

trail maps are available by calling the county Department of Parks at 495-2535.

HOWARD COUNTY

has a free Bicycle Pathway Map available from the Department of Recreation and Parks, 3300 N. Ridge Rd., Suite 170, Ellicott City, MD 21043. Call 301/992-2464.

CITY OF FAIRFAX

on- and off-road bike routes are outlined on a map available by writing Parks & Recreation, 3730 Old Lee Hwy., Fairfax, VA 22030. Call 385-7858.

Take the Train, Wear a Helmet

IF YOU DON'T have a car but are still interested in sampling some of these trails, don't despair. You can take Metro.

The Washington Metropolitan Area Transit Authority allows cyclists to bring their bikes on the Metro on weekends, on all holidays except the Fourth of July, and after 7 p.m. on weekdays. But you need a pass, which costs $15 for five years. It's available after you attend a 30-minute class and take a simple test on the rules of use. Classes are offered Mondays at noon and Tuesdays at 8 a.m. at Metro headquarters, 600 Fifth St. NW (Metro: Gallery Place). During peak season (April through October) you can take the test the first Wednesday of each month between 4:30 and 6:30, and the first Saturday between 10 and noon. For more information, call 962-1116.

Whether you've reached the trail by bike, car or train, enjoy the scenery but watch out for your safety. Many accidents occur on bike trails because cyclists get so enthralled by the sights surrounding them that they don't look where they're going. A few other pointers for safe cycling:

Wear an ANSI or Snell-approved bicycle helmet. Most allow airflow and white ones will reflect heat, so don't worry about getting too hot. A helmet onced save my life when I hit the pavement to avoid striking a car.

Don't use radio or cassette players. Headphones block out bells, sirens and other sounds you'll need to hear.

Sound a bell or horn when you pass another cyclist or pedestrian. If you don't have a noise maker, give an audible warning such as "Passing on your left."

Wear bright clothing. It makes you more visible, even in daytime.

Wear biking gloves or pad your handlebars, and keep your tires inflated to the maximum suggested level to absorb shock from bumps.

Drink plenty of fluids to avoid dehydration. Always carry a water bottle.

Test your brakes before each ride. And note that brakes that work when it's dry may not work in the rain.

Area bike trails have been the scenes of assaults. Women should exercise caution when riding alone.

Freelance writer Charles Pekow can be found most weekends astride his 12-speed.