Hiking in the fall is a precious moment. All too soon there will be confinement to winter quarters. And with the leaves down and crackling underfoot, you can see deeper into the forests and farther over to the next peak of the mountains and hills west of Washington.

Hiking in the fall means being prepared for both the chill of the morning start and the warmth of a vigorous climb that heads for open space and the noonday sun. You'll be carrying a knapsack -- a hike isn't a hike unless you've packed lunch or at least an elaborate snack -- but leave room for the layers of clothing you'll be peeling off as the exercise and warming temperatures make you feel summery again. You'll need to wear shoes with a good tread: downed leaves are slippery, especially after a morning frost. It can't hurt to carry a flashlight, something weatherproof in case of rain, a canteen and tissues, for noses tend to run when you walk briskly in chilly weather.

With daylight failing by 5:30 p.m., hikes should start early. You want to be out from under the trees by 4 in the afternoon. If you are heading for an impromptu hike on unknown terrain, go for the western face. The light lasts just a little longer.

Here are five fall hikes guaranteed to keep you from feeling the cold. The shortest takes an hour; the longest, about five hours. They all can be done by hikers in moderately good shape. All are well marked. You shouldn't get lost. WHITE OAK CANYON. Near Syria, Virginia, at the eastern edge of the Shenandoah National Park is the White Oak Canyon trail which passes by two waterfalls, several cascades, wild rocky outcroppings and in among superb hemlock, oak, tulip, popular and ash trees. (To get to the trail take U.S. 211 west to Route 231, go south to Route 670 and west on 670 to Syria. Turn right on Route 600 'til it ends). The beginning of the trail is a comfortably mulched walkway where you're apt to see walkers (as opposed to hikers) in their Sunday-best clothes. They're taking a stroll of about three-fourths of a mile to the first waterfall.

Past the first waterfall, however, the canyon gets down to business. You'll be climbing about 1,500 feet in a little over a mile. There's help in the steepest parts from steps that have been carved and cemented into the trail. The hike is worth every huff and puff of the climb: at the headwaters of the second waterfall, you pass dwarfing cliffs, cascading waters and then, at the top of the falls, peace, quiet, calm. There are large, flat rocks baking dry and warm in the sun. You can stretch out on them for a nap and congratulate yourself for this chance to snatch time in the sun.

The trail to the second waterfall will probably take 2 to 2 1/2 hours of medium-paced, occasional rest-stop, hiking. You don't have to apportion that amount of time for the return trip. What went up the steep ravine comes down in half the time. The walk is a total of five miles.

If you want a longer hike, cross the top of the second waterfall on the rocks and pick up the Cedar Run Canyon trail which leads down the other side of the ravine and connects with the lower portion of the White Oak trail. The circuit route is seven miles and requires an early start.

There are parking areas at the foot of the canyons. Use them and not the road. Illegally parked cars are towed to Culpepper. MARYS ROCK. High above Thornton Gap (where Route 211 crosses the Skyline Drive), some 3,514 feet in the air, is Marys Rock, named for a Mary Thornton who, in 1733, slogged her way through the underbrush and made a beeline for the top. Today's trail is cleared and graded with frequent switchbacks which make the hike a lot less difficult than it once was.

Start by parking in the upper parking lot of the Panorama Restaurant at Thornton Gap. If you didn't bring a snack or lunch, the Panorama has surprisingly decent food. The trail begins at the end of the upper parking lot. It darts in and out of the trees with several good resting and viewing spots along the way. The top, a rocky outcropping and overhang, is not for those afraid of heights. Kids love it because of the rock-climbing possibilities, and the rest of the world loves the view. You feel on top of the world while the forests and mountain gaps below are miniaturized. If you're lucky to hike on a sunny day, you can count on finding a windsheltered spot where it's nice and warm. The trail to Mary's Rock is just under two miles long. The round trip can be done in two hours. STONY MAN AND LITTLE STONY MAN. Another easy and slightly longer hike to great heights is Stony Man and Little Stony Man mountains. Stony Man is the second highest peak (4,010 feet) in the Shenandoah Park, but the car does most of the uphill work. You drive to the Skyland section of the Skyline Drive (a few miles south of Thornton Gap), park and pick up the Stony Man trail. The early part of the hike is on a nature trail developed by the National Park Service which has set out signs noting botanical and geological features of the terrain.The nature trail runs between Skyland and the side trail leading to the Stony Man cliffs. A short way up Stony Man cliffs there's a trail that forks to the left and goes around the south side of the Stony Man summit. You're now about a mile from your starting point. Enjoy the view, return to the main trail and keep going on to Little Stony Man cliffs (elevation, 3,600 feet) about a mile farther along the trail.

Once again, your walk is rewarded by spectacular views. If you don't want to go back the way you came, pick up the Appalachian Trail at Little Stony Man cliffs. This trail leads back to Skyland. For the circuit route, pick up the Potomac Appalachian Trail Club map of the central section of Shenandoah National Park. These are usually available at the Thornton Gap visitor's service area or through the club, 1718 N St. Nw 20036. The map also shows White Oak Canyon and Marys Rock. BILLY GOAT TRAIL. Close to home but surprisingly strenuous is the two-mile-long Billy Goat trail which is picked up off the C&O Canal either a quarter-mile north of Old Angler's Inn or a quarter-mile south of Great Falls Tavern. Some of the challenge is provided by sections of the trail that are poorly marked and maintained.

The going can get rough but the rewards are a view of Mather Gorge where the Potomac surges over rocks between Maryland and Virginia shores and an occasional fleeting glimpse of wildlife at work -- beaver building dams, deer romping in the woods. One section of the trail goes over a long, long stretch of rock. Hard to believe it's less than 20 miles from Georgetown. The hike should take between two and three hours. SUGARLOAF.For something short and sweet that lets yoy test whether you like being out there walking around in fall weather, head north on I-270 for Sugarloaf. It's a high spot 1,280 feet above sea level, and one of the most popular local hikes for families with small children. Even the littlest of legs can make it to the top.

On the way up there are stairs built into the trail which make life easy for everyone. Coming down, the other side the path is more trail-like. It's a pretty walk, and the scenery is lovely. The crispness of fall is everywhere. At the end of the line you can stop at Comus Inn for lunch or dinner.