"The sport's full name is orienteering but the enlightened call it "O." The Washington area is on the "O-zone" edge, about as far south as O-ers generally go to O, but despite its fringe location it is blessed with the top U.S. woman in the game.

She's Peggy Dickison, 30, a wiry federal mapmaker who trains hard five days a week, sleeps in a condo cluttered with O maps and travels the globe in pursuit of competition. Her former coach, Harvard-educated Peter Gagarin, says of her:

"If you want to be any good at orienteering, you've got to be a fanatic. It has to be number one in your life with no number two. Peggy is certainly in the mold."

Though she's been at it less than a decade, the U.S. Olympic Committee has named Dickison top U.S. female orienteer the last three years. Why the USOC cares is a question, since O never has been an Olympic sport and shows no sign of becoming one. But it's an affiliate, an official Olympic "wannabee," as Dickison puts it, so USOC keeps an eye on it and, by logical extension, her.

She'd be hard to miss, having won the national championships in 1988 and '90, as well as the '88 North Americans, and having competed in Europe at the last three world championships.

So what is O, anyway, and how did Dickison get so good at it?

Orienteering is a 75-year-old pastime of Scandinavian origin that tests one's ability to rush around the woods from predesignated point to point, busting through brush and up and down hills using only a compass and a detailed map for guidance.

As contestants find the checkpoints in a race, they punch their race cards with special hole-punchers left at each spot and head off for the next one. Races last an hour or two and cover up to 10 kilometers, with winners determined by elapsed time.

The local Quantico Orienteering Club, which used to be affiliated with Quantico Marine Base but now is wholly independent, has 150 members and puts on biweekly races most of the year.

But those events, in which 20 to 30 percent of the competitors walk or at best jog the course, are tepid pablum to a fiery competitor like Dickison, who often finds herself scrambling along on hands and knees through seemingly impenetrable thickets during races, and discovers bruises and scratches in the shower afterwards "that I have no idea how I got."

The orienteer's constant internal debate, she said, is whether to battle through a thicket or take the longer route around; whether to crash down a steep, wooded slope and up the other side or sweep around it on the flatter ridgetop at the head of a draw.

At issue is never what's easiest, but what's fastest. And at her level, Dickison said, decisions are made on the fly. A good orienteer never stops to ponder; while studying a map, she's on the run.

That must make for some interesting moments, since O maps have developed in recent years into bafflingly microspecific charts of every shrub and ruin out there. As a result, scanning the average O map while running through the woods is like reading the Sunday classifieds while waterskiing.

"The hardest thing for me now is seeing the fine print," admitted Gagarin, former U.S. national team coach who at age 46 remains the third-ranked male O-er in the nation. "The map is my best friend, but I'm only getting about half the information. There's lots of little things I can't see."

Small wonder. On the O map of Great Falls, produced in 1988 by the U.S. Orienteering Commission, there are separate, tiny symbols for: "Earth bank, low earth wall, large erosion gully, erosion gully, small gully, small knoll, small depression, pit, broken ground, water hole, marsh, uncrossable marsh, seasonal marsh, narrow marsh or trickle, stream, small stream, seasonal watercourse, spring source, well or captive spring, major road, dirt road, vehicle track, large path, small path, indistinct path, narrow ride, tunnel, anthill, rootstock, boulder, rocky pit" and on and on and on ad infinitum.

"You get these incredibly detailed maps that are great if you love maps, but confusing if you don't," said Gagarin. All of which plays into the hands of Dickison, who loves maps enough to have made a career drawing them.

"It's a thinking sport," said Dickison, who put a bumper sticker on her aging Honda that extolls "Cunning Running," another of O's clever nicknames.

"It's about 50 percent mental and 50 percent physical," she said, which suits her too.

Dickison is gearing for the national championships in the early summer, followed by the worlds in Czechoslovakia in August. The United States sends five men and five women to the worlds, so she's almost assured.

But while Dickison hopes and expects to win the nationals again, she harbors no hope of setting records overseas. Over the last six years she's competed in Australia, France, Sweden, Canada, Scotland, Finland, Norway, Czechoslovakia, Hungary, Austria and England, but her best finish in the worlds is a distant 48th of about 80 in 1989.

The problem, she said, is lack of competition. "Our nearest club here is three hours away in Philadelphia," she said. "In Scandinavia, every little town has a club. There are more maps, more clubs, more people competing."

When she took six months leave from work to train in Norberg, Sweden, three years ago, "they had more activity in a town of 3,000 than we have here in a city of one million," she said.

Which means, she reckons, that the U.S. medal count in this peculiar sport will probably stay unchanged in the forseeable future:

0 for 0.

Quantico Orienteering Club's next meet is Jan. 20 at Little Bennett State Park near Gaithersburg. Newcomers are welcome. Call (301) 840-5844.