The Potomac Gorge in deep winter. Ice and snow decorate both the Maryland and Virginia shores; even down along the District shores ice rims the river banks. Only the most obdurate mallards remain in sheltered coves of open water. Up near Great Falls, the walls of the gorge cup the roar of the cataracts; on the level of the river all sound is lost except the drumming of violent water -- water that's demonic, a cold and homicidal fury only a few degrees above that of the chunks of ice that shoot through the flumes, swirl and dive in the whirlpools and turn slowly in hidden menace.

And yet the sun shines, the sky is clearing. Twigs, coated with frost overnight, drip a relief of sorts in air that weaves currents above the river, temperature hoisting slowly toward 40 degrees Farenheit. Even on the sullen Virginia shore, where the rock walls hide in continuous winter shadow, streaks run down through the cracks from the thawing mud far above.

It's a day bright and brilliant enough to lure a few hardy lovers of the outdoors to the paths in the riverside parks, bundled in layers of clothing, in long johns, sweaters and parkas and knit wool caps. An enticing day as long as the body is warm and dry.

Down in the gorge, in the linear caldron, in a thin envelope of strange weather, mists swirl as the air is assaulted by the river water. There, on some precarious edge of existence, kayakers bob, beaming frozen grins of delight in fragile cockleshells of fiberglass, surging with hot arms and shoulders against the will of the river.

Bill Kirby, 27, is one of Washington's durable core of kayakers. He plays on wild rivers all year, loves the spray of a standing wave whether it cools him in summer or frosts his black mustache in winter. Ten years of the sport have given his upper body bulk, as if he could paddle on the river without his boat, all massive chest and shoulders above the foam.

Kirby is a Ranger at Great Falls National Park. As "honcho" of water safety, Kirby runs a crew that spends a lot of the summer in the water in rescue boats.

"I'm getting paid for what I love to do anyway," he says.

Kirby's job is only for 10 months of the year. During the winter, business is slow at the park so he has two months free to hunt and ski and run rivers.

"In the winter I paddle in the Potomac just for the scenery and the excitement," he says.

"A few years ago, a friend and I put in down near the Old Anglers Inn and paddled up into the gorge. It had been really cold for a long time and there was a lot of ice on the river.

"But it was warming. I think the temperature went all the way up to 45 degrees that day. And a big, flat piece of ice broke loose from some eddy and came down to us."

Kirby wiggles his thick arms and shoulders. "We got on top of it; just paddled and squirmed into the middle like a couple of walruses and rode it down the middle of the river.

"We stayed with it until it started to break up in the rapids. It weighed maybe a ton. One chunk could have gone right through the boat."

Even then, the Potomac is relaxation and giggles for hard-core kayakers. For real fun, they head for the upper stretches of the Rapidan or Shenandoah in February when the smaller branches and tributaries are swollen with heavy precipitation, both rain and snow.

The Potomac is so big and deep that if one of the fragile kayaks were sunk the swim to shore would be too uncomfortable, courting an unreasonable risk of exhaustion and hypothermia. "The Potomac's bad enough to go down in summer," says Kirby. "You can get real tired getting out.

"This small tributaries are narrower and not too deep, so it's easier to get yourself out."

Aside from his kayak, the paddler's main line of defense against the killing water is a wet suit, similar to but thinner and more flexible than a diver's. The outer skin of the suit is impermeable neoprene. The inner, warming, layer is an open-celled foam, which, according to the theory, traps a warm layer of water next to the body.

There is, though, the small outrage of acquiring the layer of warm water.

"In the winter you have two choices," says Kirby. "Avoid it or go ahead and take it right away -- get it over with. On the Potomac you can sometimes avoid it altogether and just enjoy the scenery."

Kirby cringes and hesitates just trying to talk about it. On the small rivers the soaking is inevitable, a thing that has to be faced when the paddler wakes in the morning and reluctantly leaves a warm bed and looks out his window and sees how cold it is.

"Sometimes I'll have a trip set with friends and get up and say, 'Damn, this is crazy.'

"The first water into your suit is bad, but then you're all right. The rocks are covered with ice, maybe there's some snow coming down, but you're comfortable and having a good time.

"But the first time it's as if someone put your big toe into an electric socket. You're gasping for 15 seconds."

It's also painful getting out of a wet suit beside a car on a country road and trying to get into warm clothes when a cold wind is blowing.

But the worst, according to Kirby, is getting back into a cold wet suit the second day of a weekend trip.

"Sometimes it's frozen," he says. "You can hold it straight out by one foot."

Still, once in the suit, with a tepid layer of water next to the skin, it's worth all the pain to be on the river.

"You feel you're getting away with something," he says.

White-water canoeing carries its own year-round dangers and challenges and demands skills that are earned only with experience. Kirby estimates that any stretch of water is a degree of magnitude more difficult in winter than in summer.

"So you're a lot less aggressive in the winter," he says.

He once ran rapids in West Virginia in five-degree weather.

"We had to go over to the side every few minutes and bang the ice off our paddles," he says. "Being out in those conditions and being all right was great."

It's the excitement of speed, avoidance, survival.

Down in a wild river, picking a way through rocks that can smash his bright little boat and crush his bones, following torrents that can modestly swamp him, suck him away from light and air, fill his lungs with alien matter, the hardcore paddler pushes his own knuckle of determination, rides his own warm center in cold capable of snuffing his life like a breath on a birthday candle.

In the winter Kirby and his friends are out of traffic. Their cars are likely to be alone at the remote put-in points. Warm weather can bring too much competition for the river, not just hunters and fishermen, but the new masses of canoeists and kayakers.

When Kirby first took up a double-bladed paddle, a kayak was rare. The clubs in the Washington area had membership lists of only a few hundred and most of those members were only occasional paddlers.

"We had an explosive growth from about 1971 to 1976," says Kirby. "Then it leveled off.

"The problem, I think, is that in the past few years the trend has been away from the clubs. Now people can buy kayaks all around, so they can get equipment without the learning they need.

"There's less concensus on what's safe, what's right. The sport is not as unified as it once was."

The number of wild rivers is finite but their use is still growing. Access to some streams on private land is being closed off because of litter and other abuses.

But the accident rate seems to be going down, according to Kirby: "The 'Deliverance Syndrome' is wearing off."

Still, on fast water the danger is always there, and in the winter even the best equipment and determination allow few mistakes.

Fast water doesn't freeze even when it has coated all its edges with ice. But every river has its quiet pools, its eddies, and slack stretches. These can freeze.

"If a section of ice goes all the way across the river and the current is going under it, you're going to go under it, too," Kirby says.

"It's okay if it's only five feet across. But if it's a quarter of a mile you won't be able to hold your breath long enough."