Up from the meadows rich with corn,

Clear in the cool September morn,

The clustered spires of Frederick stand

Green-walled by the hills of Maryland.

From "Barbara Fritchie,"

by John Greenleaf Whittier.

IT IS EARLY FALL and bicyclists, like migratory birds, are flocking to Frederick Valley as they have since the 1880s. They come to pedal through a peaceful 19th-century countryside that still preserves its covered bridges, farms and orchards and quiet back roads with more rabbits and crickets on them than cars.

But mostly the cyclists and tourists come to see the rainbows of changing autumn color on the Catoctin and South mountains and to enjoy village festivals. There are two this weekend, in Thurmont and Frederick, with hundreds of local arts and crafts booths and huge tables of freshly cooked farm food.

Balancing on two wheels is not the only way to see Frederick Valley and the fall foliage. It can be done from car and train windows, by canoe, by hot-air balloon or slowly on foot. Presidents do it by helicopter, en route to Camp David, the First Gentleman's retreat in Catoctin Mountain National Park, just up the hill from Thurmont.

But spinning silently down country lanes and rumbling across covered bridges with streams visible between the floor boards can be an exhilarating way to experience the valley.

Motorists, even with their car windows open, pass through too quickly and never feel close to the countryside. Cyclists, however, will remember every farm house and cross road, all the barnyard sounds and smells. They will hear quail and songbirds and blackbirds, which in the 1970s invaded Graceham, overwhelming the valley village of 400 residents with thousands of starlings, grackles and cowbirds.

Cyclists will develop close personal relationships with numerous small Frederick hills, though the county's scenic Three Covered Bridges bike route (outlined in the accompanying map) manages to avoid the mountains even as it provides a panoramic view of them. The covered bridge ride, which can be 32 or 47 miles long depending on where you start, is the most popular bike ride at the Frederick Fall Foliage Frolic, the annual romp of Washington's Potomac Pedalers Touring Club. The club's two-day, two-wheel extravaganza next weekend will bring more than 500 cyclists to the county. (The overnight outing, with accommodations, is already booked this year. For information on next year, write the PPTC, P.O. Box 23601, L'Enfant Plaza Station, Washington, D.C. 20026.)

The 47-mile route starts in the city of Frederick, which has a large and beautifully preserved historic district. The city is still filled with the church spires of John Greenleaf Whittier's day but also has on its horizon the huge antennas and satellite disks of Fort Detrick -- the U.S. Satellite Communications Center, which is part of the "hot line" between Washington and Moscow.

Among the city's early buildings are Rose Hill, the colonial mansion of Thomas Johnson, Maryland's first governor; Schifferstadt, one of America's finest German colonial buildings; and the reconstructed brick house of Frederick's legendary octogenarian heroine, Barbara ("Shoot if you must this old gray head, but spare your country's flag") Fritchie.

On Saturday, from noon to night, Frederick will hold its annual seven-block-long In-the-Street festival, featuring hayrides, dancing, a foot race and bike race and continuous music, food and beer.

For those who are able to pedal away from Frederick, the 47-mile loop ride takes cyclists through the valley's three 1850s covered bridges and into Thurmont, at the foot of the Catoctins. (The 32-mile loop starts outside of Frederick at almost any place you can park your car.)

Thurmont is holding its 23rd annual Colorfest Saturday and Sunday from 10 a.m. to 6 p.m., with its churches, schools and parks filled with ethnic food and more than 330 arts and crafts booths. Three trains a day leave town on hour-long foliage rides into the mountains. (The rides -- $5 for adults, $3 for kids -- begin at noon, 2 p.m. and 4 p.m.; for further information, call 301/775-2520 or 775-7718.)

In any case, odds are that the best ways to get around Thurmont and Frederick this weekend will be on foot or bicycle.

Getting around Frederick County by bicycle has been a tradition for more than a century.

In 1883, according to a Washington bicycle club magazine, club rider L.W. Seely and a friend had a delightful fall ride through the Frederick Valley, fashionably attired in knee britches, stockings, coats, white flannel shirts and cork helmets.

They crossed into neighboring Carroll County, where they bicycled on their high wheelers past the home of former Maryland governor John Lee Carroll, "whom we met on the road and with whom we had a pleasant conversation." It's the kind of thing that happens when you get on a two-wheeler. CYCLING SEASON

A lot of bike outfits are particularly active at this time of year. Here's a look at what's going round.

ARLINGTON CLUB leads scenic trips for novice and family bikers, leaving from Thomas Jefferson Center. Call 276-7751 or 558-2871.

AMERICAN YOUTH HOSTELS Potomac Area Council has Eastern Shore outing Oct. 18-20; register by Oct. 15. Gettysburg foliage outing Oct. 25-27; register by Oct. 22. Call 783-4943.

CHESAPEAKE & SHENANDOAH TOURING has country inn weekend trips. Call 332-7166.

CHESAPEAKE TOURS has Eastern Shore weekends. Call 301/876-2721.

COLLEGE PARK CLUB has rides, races, training sessions, newsletter. Call 864- 2211.

HEY-BIKE (439-2453) is the number to call for up-to-date information on area bicycling news.

INN FINDERS has touring workshops, day trips in Eastern Shore, Tidewater, Pennsylvania Dutch & Shenandoah areas. Call 525-2906.

OPEN ROAD TOURS has weekend country inn outings. Call 754-4152.

OXON HILL CLUB has Southern Maryland daytrips. Call 839-4270.

POTOMAC PEDALERS has area rides for beginner through expert. Call 363- TOUR.

PRINCE WILLIAM TOURING CLUB has outings most weekends. Call 703/494- 5252.

WASHINGTON WOMEN OUTDOORS have Berkeley Springs, W. Va., outing Oct. 19-20; Pennylvania Dutch outing Oct. 26-27. Call 797-8222.