The vice chairman of the Potomac Appalachian Trail Club's mountaineering section hates chalk.

"It's obnoxious," said Stuart Pregnall, a bearded 31-year-old financial analyst who works in the office of the Capitol architect.

"It mars the rocks and it takes away from the challenge of the sport, because every move is obvious before you start," he said last week as he peered over a cliff just below Great Falls, and mapped strategy.

Under the cliff lay a nasty little rock climb called Armbuster, a 45-foot vertical ascent up a crack where two perpendicular rock walls meet.

It would have been a far more difficult strategy to plan if every spot where climbers had gone before wasn't marked by white smudges of chalk identifying the handholds they'd used.

Chalk on the hands helps climbers gain a grip and can make hard ascents a bit easier, according to Pregnall, particularly around Washington, where the hot, damp summers make the rocks slippery. So most climbers hang bags of the dusty powder from their belts and use it whenever the going gets tough.

But in Pregnall's view, the whole idea of rock climbing is to use your wits and skill to tackle something hard and uncharted, not just to conquer rocks. And he doesn't like following somebody else's lead.

So Pregnall won't use chalk. "But I'm probably one of about four people in the country who doesn't," he said with a sigh.

Pregnall reckons there are about 1,000 climbers these days in the Washington area, which is a hotbed for the sport because of the proximity of excellent practice areas at Carderock on the Potomac a few miles above Washington, and at Great Falls, a little farther upriver.

These areas have been popular with climbers for a half-century, Pregnall said, but nowadays the base of interest is broadening. Enough folks are involved that a new book cropped up this summer identifying the popular climbs at Great Falls: James Eakin's "Climber's Guide to the Great Falls of the Potomac."

Eakin put funny names on some of the climbs: Overhead Smash, the Crypt, and Stop the Presses, Mr. Eakin; Executioner's Song, Backslider, Randomly Vicious, Monkey Fingers and Lunging Ledges; Monster Manly, Poison Ivy Gully and Wall of Da Feet.

Names like that are what give aging outdoor writers and others who value life and limb pause about engaging in sports like rock climbing.

But climbing at Great Falls, at least the way Pregnall and his girlfriend, Karen Roussell, do it, turns out to be challenging but not particularly dangerous.

"The beauty of these climbs is that they're all short and they all can be top-roped," said Pregnall. "So it's very safe."

He was rigging a top-rope for the Armbuster climb, anchoring sturdy line to a scraggly-but- strong oak tree on the ridge above the rock wall. "The only way you can get hurt is if you mess up the knots," said Pregnall, checking his bowline, "and that's inexcusable."

At the foot of the climb, Roussell ran the safety rope through a pulley arrangement on her harness and took a seat. Pregnall tied the end of the line into his harness.

The mechanical advantage of the pulley would give Roussell the power to stop Pregnall's descent if he fell, even though he outweighs her, Pregnall said. Then she could lower him to safety.

But that turned out to be unnecessary as he scampered easily up Armbuster, jamming his hands into the cracks between the perpendicular rocks, bracing his feet on the facing rock walls and hoisting himself up the short ascent.

"You made it look too easy," said Roussell, who went next and made it look harder.

After that, Pregnall tackled Z-Slash, an extremely hard climb 20 feet away from Armbuster, which gives an idea how abundant climbing opportunities are around Great Falls. He got to the crux of the climb up a sheer rock wall three times, but each time failed to gain a foothold and slipped off, Roussell stopping him neatly.

Later Pregnall rigged a top-rope for the old outdoorsman, who scratched and clawed his way up the bunny slope while Roussell shouted instructions from below and diplomatically stifled her mirth.

Suddenly, daylight gave way to gathering dusk. A wild goose flew up Mather Gorge and a blue heron floated by, croaking noisily.

It was a nice night. You could barely see the chalk marks.