Even the seven carbide lamps don't dispel the darkness of the small cavern or show how deep the crevices are.

A smooth, oval phreatic crawlway, a passage little more than 10 inches high eaten away by water and long since dried out, offers better visibility, but the lamps give off an opaque glow, as if the ceiling and floor are liminous.

Wriggling along the 20-foot-long passage, using feet, elbows, knees and chin, is agonizinly slow. At a particular awkard curve, a bump on the ceiling brings down glasses, scarf and miner's helmet in front of my face.

I'm stuck! And I can't see or move until the tightly wedged helmet is back on top of my head. My carbide lamp is leaking.

Forget about turning around - it's only 24 inches wide here. If claustrophobia is going to set in, now's the time. Visions of my obituary loom before me. What am I doing here?

Spelunking.

Any fan of sunshine and fresh air may find it difficult to understand, but quite a few folks throughout the United States get their kicks crawling through small holes into mud- and water water-filled caverns - at least 10,000 to 20,000 each year, according to John Powers of Sligo Grotto. These intrepid spirits acutally relish wading through underground streams and rappelling down endless pits to their reward: a grotto with hauntingly beautiful formations. Even better is being the first to discover a new cave untouched by human hands, or feet, or knees.

Bats, "friendly" rats, lizards and albino crickets are often encountered in grottos less frequented by humans. Salamanders and an occasional snake can also be found down there. Wildlife seems to have been replaced with empty beer cans and bottles and candy and cigarette wrappers in the cave I recently slid into.

In Jones Quarry, West Virginia, where I caved the other weekend with five members of Explorer Post 250 and Maryland legislator Don Munson, many past visitors have burned their signatures on the cave walls with carbide lamps. Stalagmites (formations growing on the cave floor) and stalactites (from the ceiling) have been broken off as souvenirs. Hundreds of years will pass before the limestone deposits reaccumulate.

The recently passed Maryland Cave Act (which Munson sponsored) prohibits removing any subterranean formations, littering or depositing dead animals. It also free property owners from any liability for accidents in caves on their land. There are similar laws on the books in West Virginia and Virginia.

Spelunkers (or speleologists, as the scientific cavers are called) make a sharp distinction between themselves and the casual adventuerer, who goes down for a lark, armed with only a book of matches or a candle. Many times the latter get lost or injured.

Any caver will quickly recite some basic rules of survival when traveling to the underworld:

Always carry three sources of light - a carbide lamp, a flashlight and a candle - in case one of the sources fails. An explorer using his or her third source of light, having exhausted the other two, should be well on the way out of the cave.

Never go alone or with only novices - make sure there's at least one experienced person in the party. (There were five in mine.)

And just in case, let someone know where you're going and when you expect to return. The police have a list of volunteers for cave rescue missions.

But don't let that scare you off. With the proper equipment and some knowledgeable companions, caving is challenging and enthralling. For me it was a delicate balance between sheer terror and amazement. Fear and panic when I couldn't believe I would negotiate a long step over a dark abyss onto a ledge with a square inch for my foot. Wonder and excitement when I made it into a grotte with exquisite formations: cave coral (nubby bumps that feel like barnacles), draperies and bacon rind (which look like their names).

Being properly outfitted for a summer cave (temperature 52 degree F) requires coveralls, heavy jeans, undershirts, flannel shirts, heavy leather gloves, hiking boots and miner's helmet. Sandwiched inside all these layers, it's surprisingly fun to crawl through that sticky mud.

"I haven't done this since the army," gasped Munson as we slid on our back feet first through the tiny hole of a cave entrance. I was silently grateful another neophyte had come along.

As in any Outward Bound experience that pushes participants beyond their accustomed barriers, cavers are hindered more by psychological than physical limitations. Claustrophobia is the biggest problem.

"It's especially important for beginners to know when to stop," says Explorer adviser Tony Hopkins. "After seven or eight hours, you get very tired and inefficient. That's when accidents can happen."

After 90 minutes of mud-covered rock-climbing in Jones Quarry, every muscles in my body was shaking. Facing another sheer precipice with the usual dark abyss below, I suddenly knew I'd had enough.

Braving a tedious and slippery climb out into the sunshine, we all celebrated our successful adventure afterward with the caver's staple - an ice-cold beer.