NEARLY 30 YEARS AGO, one of my college classmates, a marvelously muscled guy who was forever going off on outing club trips, fell and broke a leg while rock climbing at a cliff. I recall wondering at the time how anybody could be so foolish as to risk life and limb in that fashion. I still have no idea how he came to fall, but I now know what he was doing out there.

Rock climbing, it turns out, is an exhilarating sport that almost anyone in reasonable physical shape can enjoy. It can provide a sense of great accomplishment, as you look down at what you came up, and think, "Hey, I just did something special."

Maybe you did some delicate balance climbing, or perhaps used a jamming technique -- which is exactly what it sounds like -- to turn a vertical slot in the rock into a secure handhold. Or maybe you just got up.

Whatever, you met a physical and mental challenge. You moved your body with careful control, made it do what you wanted it to do.

And in the process you may have reached the top of something that is otherwise inaccessible, such as Wyoming's spectacular Grand Teton or its lower but fascinating neighbor Mount Moran. Standing on such summits provides a feeling that is like no other.

Rock climbing is a sport for both men and women, with the latter usually at a disadvantage only because they typically are shorter than men and can reach fewer handholds.

The climbing basics are so easy to learn with good instruction that, unlike with many sports, there is no long period of struggling just to reach the hacker level. After only a couple of days, rank novices -- including children -- can safely climb moderate routes that before would have looked impossible.

On the other hand, unless you can find a way to climb and never get more than a few feet above where you would land if you fell, you do ned a instructor and the equipment he or she will have. The essence of safe climbing is being protected in case of a fall, and for that you'd better have some help.

As easy as it is to get started, two days or two weeks won't make you an expert, of course. The best climbers, like competitors in ice skating or diving, exhibit an effortlessness of movement, a concentration on style that can approach those of ballet. When you see a truly accomplished climber, whether by the Potomac River in Mather Gorge or high on a rock face in the Tetons of Wyoming, you will know it.

For the beginner, getting up at all is the payoff. For the expert, it is getting up in style.

The Washington area is a fine place to begin to climb. Most weekends, dozens and dozens of climbers head for cliffs on both sides of the Potomac just a few miles upstream from Washington. There is more climbable rock not far away in Maryland and Virginia. Seneca Rocks, 170 miles away in est Virginia, has some of the best climbing in the eastern United States. And there are plenty of climbing instructors.

Early one Sunday this summer, a group of six beginners, only one of whom had ever been on a rope before, gathered in Great Falls Park on the Virginia side of the Potomac. They had signed up through the Open University to take a $35, one-day introduction to rock climbing offered by Potomac River Tours of Bethesda.

The group's instructor, Priscilla Holberton, a researcher at the Smithsonian, first helped them put on their harnesses -- nylon waist straps and leg loops to which the climbing rope is attached for protection. Then she explained the fundamentals of how to "rope up" and how to handle the rope to protect another climber, a process called belaying. When the group moved to the bottom of the cliff just above the river, Holberton demonstrated how to move on the broad, slanting rock face known as Romeo's Retreat.

(One of the curious things about rock climbs is that each identified route has its own name, normally given by the person or group that first climbs it. Next to Romeo's Retreat is the much more difficult Romeo's Ladder. Just upstream, naturally, is Juliet's Balcony.)

Asked why they had decided to try climbing, one of the six, Lee Langford, replied simply, "The challenge. I'm in an office the rest of the week." He was one of the two students who late in the day attempted Romeo's Ladder.

Another of the students, Chris Brewer, said he had come out because climbing looked like "an interesting thing to do, and to see if I could do it. You know it's not exactly like playing volleyball. There's an element of danger."

Of course there is. Probably dozens of climbers are killed each year across the country. (On the woods road to the base of Seneca Rocks is a plaque in memory of a Pittsburgh woman who was killed there.) Many others get injured, but not just because their hand or foot slipped and they fell.

Climbers "fall" all the time, and normally they suffer, at worst, a skinned knee or a barked knuckle. That's because modern-day climbers go to great lengths to protect themselves in case they do fall.

When a climber is seriously injured, it is usually because a mistake was made in his protection or because he had pushed himself beyond his ability in a situation in which good protection was not possible. A climber absolutely cannot hurry. The rope and the placement of his protection must be checked and double-checked. Only some overriding danger, such as falling rock or lightning, should ever cause a climber to hurry.

The essence of a climber's protection is the climbing rope and the route along which it runs. The lead climber must take great care not to climb too far above the last "point of protection" -- a place at which the rope runs through an oval or D-shaped aluminum clip, called a carabiner, that is attached to the rock using some type of wedge-like device inserted into crevices or cracks, or perhaps to an outcropping of rock or a tree circled with a sling of nylon webbing.

If a leader falls, he falls twice the distance he has climbed above his last protection point, and then some more as his climbing rope stretches. Climbers coming afterward are belayed from above by the leader, and if they fall they do so only to the extent that there is slack in the rope and the amount it stretches. So leading is the true challenge.

The point of being "roped up" is entirely protection. Climbers do not haul one another up cliffs. A climber is supposed to get to the top using his own feet, legs, knees, hands, arms, back and, most of all, his head. Even having the belayer put tension on the rope to give an assist is frowned upon once a climber is past the novice stage.

The rope is also used for rappelling, a process of descending a rock face. Rappelling -- by sliding down the rope -- can be thrilling and, to the uninitiated, may seem the essence of rock climbing. But more experienced climbers avoid it, if possible, because it's dangerous. Rappelling is one of the few times during a climb that a climber must rely entirely on his equipment. If it fails, he falls.

The rope, then, is the one absolutely essential piece of climbing equipment. Small wonder that serious climbers are notoriously touchy about their ropes; their lives could depend upon them.

The ropes in use today are made almost exclusively of perlon, a man-made fiber. It is strong, it generally resists abrasion, and it stretches, but not too much. The stretch is very important because that absorbs a significant portion of the energy of the fall.

During the afternoon of the Potomac Tours climbing class, two people fell -- Langford and the other student who attempted more difficult routes, Jennifer Smith, a University of Maryland graduate student. Neither was hurt. They simply swung into the air and fended off the rock with their feet.

Smith, who had spent one previous day climbingwith a friend some years ago, seemed instinctively to have the sense of balance enjoyed by really good climbers. In short, she kept her weight carefully balanced over her feet.

That sounds like a simple matter, but for most beginning climbers, including some of the others in the class, the instinctive tendency is to hug the rock even on very moderate slopes. Unless the rock is very steep, leaning into the cliff means that as a climber puts his weight on his carefully placed feet, much of the force is really being exerted parallel to the cliff face and is, in effect, pushing his feet off their hold.

"Get your butt out," is a standard cry from climbing instructors from coast to coast. It is not instinctive to lean outward that way, but it works.

A few weeks earlier at Seneca Rocks in West Virginia, a couple of beginning students at the highly respected Seneca Rocks Climbing School had tried to overcome that hugging imperative. Ron Becker, an assistant director of the Smithsonian's National Museum of American History, and Jose Lopez-Vargas, a programmer and cartographer at the Defense Mapping Agency, had come out for some of the same reasons as the Open University group: a chance to be outdoors and to challenge themselves. "I've spent too many days in inside spaces," said Becker.

When Becker reached a secure point, his guide from the Seneca Rocks Climbing School carefully showed him how to use his end of the climbing rope to attach himself to a protection point set in the rock. Then, for the first time, Becker looked down the vertical east side of the blade-like band of sandstone at Seneca Rocks, and murmured, "Oh my god!" But he was determined to continue what he had started. The exposure did not seem to bother Lopez-Vargas.

Some people go climbing specifically to overcome acrophobia, a fear of heights that can be severe. On another summer Sunday, a middle-aged man appeared at the base of Romeo's Retreat with an acquaintance who was a very experienced climber. The man's acrophobia once had been so bad, he said, that he could not stand to drive across the Cabin John Bridge on the Beltway. He had licked that part of his fear and now had come climbing to see if he could lick it all. He moved gingerly on the cliff, testing more his ability to stand the exposure than to learn to climb.

For some people, acrophobia could be an absolute bar to rock climbing. For others, climbing could be a way to come to grips with it. A substantial number of climbers say they have suffered from such a fear at one time or another in their lives.

Nor are some other types of handicaps necessarily a bar. One Washington family went on a driving vacation through the West this summer and spent several days camped by Jenny Lake in Teton National Park. A son who is moderately handicapped mentally and has difficulty with his gross motor skills spent two days taking climbing instruction along with his father. "When he finished, he felt 10 feet tall," his father said later.

Indeed, he had had the thrill of doing something special -- more special for him than for those without his handicap. Because of the boy's coordination problems, his father wanted special care taken to protect him against injury. As it turned out, exactly the protection provided any climber did the job.

I started rock climbing a year ago because, as an avid hiker, I wanted to go to the top of Grand Teton. There is no way to do it safely without the protection of the rope. Some of the routes are not very difficult climbing, but at one point a misstep could drop you 2,500 feet down into Valhalla Canyon.

My 14-year-old son and 12-year-old daughter made it to the top with me. My wife, who has acrophobia, went only to a camp high on the 13,770-foot peak. But since then she has climbed in Mather Gorge and in New Hampshire, and she now has her own rock climbing shoes, too.

ROCKS WITHIN REACH

Washington is hardly located in the mountains, which is where most people would asme you have to go to find good climbing rock. But there are numerous good places to climb, some only a few minutes' drive. Among them are:

GREAT FALLS PARK, Va. -- The climbing cliffs stretch for more than a mile along the Potomac River in Mather Gorge below Great Falls and offer every degree of difficulty. One of the attractions here is that no one has to lead the climbs since the cliffs are approached from the top. Trees, webbing and carabiners are used to provide a point of protection at the top of the climb while the belayer stands at the bottom of the cliff -- a system known as top-roping.

To get there, use Beltway Exit 13, on the Virginia side of the Cabin John Bridge, taking Route 193 upriver for about five miles to the first traffic light. Turn right and enter the park. Free maps of the park and a new $6 climbing guidebook are available at the visitors center.

CARDEROCK RECREATION AREA, Md. -- A smaller series of top-roping cliffs even closer to downtown Washington.

To get there, take Beltway Exit 40, the first on the Maryland side of the Cabin John Bridge. Go upriver on the George Washington Memorial Parkway to the first exit, cross over the parkway and enter the park.

GREAT FALLS RECREATION AREA, Md. -- This area across from the Virginia park has several good climbing cliffs but they are somewhat more scattered than than those in Virginia. The $6 guidebook mentioned above also covers this area.

To get there, proceed as if going to Carderock but continue upriver on the GW Parkway to MacArthur Boulevard. Take MacArthur Boulevard to its end at the park, about five miles from the Beltway.

SUGARLOAF MOUNTAIN PARK, Md. -- A beautiful hiking and climbing area just north of the Montgomery County line in Frederick County.

To get there, take I-270 north from the Beltway about 25 miles to the exit for Route 109. Go west and south on Route 109 to Comus Road and turn right. Follow Comus Road to the park entrance, which is about five miles from I-270.

SENECA ROCKS, W.Va. -- These rocks, about 170 miles from Washington, are regarded by many climbers as some of the best in the Eastern United States. Climbing routes must be led, and the exposure to heights gives a much different sensation than the lower climbs along the Potomac. Again, there are routes offering every degree of difficulty.

To get there, go west on I-66 from the Beltway to its end at I-81; go south on I-81, take the exit for Strasburg. Follow U.S. 11 into Strasburg, turn right on Route 55 and continue into West Virginia. Seneca Rocks is 22 miles south and west of Petersburg at the intersection of West Virginia Route 55 and U.S. 33.

There is a good National Forest campground a few miles west on U.S. 33, or climbers can camp around the parking area for the rocks themselves. There are motels in the area; one, the 4-U, a short distance south of the rocks, serves very good and very inexpensive breakfasts. Guidebooks, climbing gear and information are available at The Gendarme in the village at the intersection.

ELSEWHERE IN THE EAST -- There are many excellent places to climb that are a long day's drive or less from the Washington area. Among them are the Shawangunk Mountains near New Paltz, N.Y.; and the White Mountains of northern New Hampshire.