The thermometer was down toward zero on Catoctin Mountain, with the wind whipping the world to the equivalent of 40 below, and Ken Jeffries was disappointed.

Jeffries was presiding over the inaugural hike along the new Goodloe Byron Trail, which he and other stalwarts of the Potomac Appalachian Trail Club had been working

on for six years. "This weather has messed us up," he said, surveying the 20 hikers steaming through the woods in the bright thin sun. "If it had been really cold, or we'd had a snowstorm or something, we'd have turned out a lot more folks. PATC members seem to like a challenge."

It seemed plenty cold to suit one late arriver, who had been delayed by a frozen fuel line in his car. His nose went from cold to painful to numb in the first hundred yards, and the finger he exposed to press his camera shutter would go stiff in a minute or two. Jeffries' complaint, apparently, was that, while it was cold enough to freeze one's cheeks board-stiff, it wasn't cold enough to actually crack them.

PATC members labor the year round to maintain vast stretches of the Appalachian Trail. That by itself isn't hard enough, so they build and maintain scores of other trails, from Rock Creek Park to the wilds of West Virginia. Weekends not spent making trails are spent hiking them, generally at an army route-march pace.

Jeffries' group went storming along, up hill and down dale, over rocks and rills, through open oak and thick pine woods, in a swirl of leaves and the vapor of healthy lungs. Tom Floyd, supervisor emeritus of trails for PATC, adopted a more modest pace because he had been asked to recommend improvements to some of the six-mile stretch of the trail being traversed that day. Floyd opined to a panting companion that the trail was unnecessarily steep in places, amen, but Floyd's concern was not so much for limp-legged hikers as for erosion.

The Goodloe Byron Trail, named for the late Western Maryland congressman and outdoor enthusiast, will be maintained by volunteers from the Catoctin Trail Club. It snakes along for 20 miles through Gambrill State Park and Catoctin National Park between Frederick and Thurmont, connecting several old trails and logging roads.

Along with glimpses of the surrounding valleys it offers dramatic rock formations, secluded hollows and leafy laurel thickets. There are deer to be seen, also; the best technique is to sit down and wait for other hikers to come pushing them along.

The long project's appeal to Jeffries and such tireless helpers as Henry Wagley was "the chance to offer a deep-woods experience in a place that's so close to main highways and to two major cities. It's a backcountry trail in the suburbs." The southern end of the trail is a few miles from U.S. 40 and about 90 minutes from downtown Washington or Baltimore.

The full trail would make a long day for a hardened hiker, especially one who likes to look at something besides his toes, but takeout cars can be spotted at intermediate points. Maps and advice should be sought from the federal or state park offices.