Two rubber rafts, 15 nervous souls aboard, bobbed in the quiet water a half-mile above treacherous Big Nasty rapids on the Cheat River last week. The water temperature was in the 40s, the air was 32 and a whistling wind bore snow along in slanting sheets.

No one said a word.

"Did you notice it, too?" guide Jim Kenny said later. "It was so quiet. You didn't have any of the things you normally get on a raft trip -- the water fights, the fooling around. People took it seriously."

You could hear the snow hit the water with a hiss and you could hear the thunder of the rapids beyond -- Beech Run, Big Nasty, Even Nastier, Aphrodisiac Falls, Zoo Rapids, Teardrop, High Falls, The Maze, Colisseum, Pete Morgan and Killer Falls.

It was two rubber boats and a big, cold, noisy river, and the certain knowledge that if you got soaked, even in a wetsuit, you'd be a miserable puppy until you got back to civilization at day's end.

"I can't say you won't go swimming," Imre Szilagyi, who runs Appalachian Wildwaters, had said that morning. "I can say that we run thousands of these trips every year and the chances of getting a serious injury are less than one in a thousand."

Despite the cold, none of the 11 paying customers on hand, who had driven from as far away as Covington, Ky., backed out of the $40 ride down the rambunctious Cheat, which roars through wilderness for 11 miles below Albright.

They put their safety and their lives in the care of Szilagyi's judgment, his equipment and his guides, which is the leap of faith you make when you jump in a raft and set off down a wild river.

Two miles downstream lies Big Nasty, roughest rapid in the canyon, where the Cheat narrows into a deep, fast chute and roars over a rocky drop into a churning, five-foot standing wave. It's nastier now than ever, Szilagyi said, and harder to avoid after floodwaters gouged the river bottom out and redirected the channel straight down the throat of Big Nasty.

"It's hard to stay out of the hole, and we have some concern that at certain levels the hole could be a 'keeper' now," said Szilagyi. A "keeper" is nature's equivalent of the now-repaired "drowning machine" at Little Falls Dam on the Potomac, where water reverses direction below a falls, trapping whatever goes over in a recirculating pattern that alternately dunks and manhandles its victims, but won't let them wash through.

"Last weekend, hundreds of rafts went through Big Nasty and about three-quarters of them capsized," said guide Rob Stout, "but it was 85 degrees out. Some people got banged around on the rocks and I guess some were held under water longer than they wanted, but nobody got hurt. Today, I don't want to go swimming. I'm going to do everything I can to stay out of that hole."

So there we sat in our wetsuits, one rapid away from Big Nasty, waiting very, very quietly for our voluntary brush with cold destiny.

Thus starts another season in the curious "adventure/travel" trade of whitewater rafting, which has bloomed in the last 20 years into a major recreation industry.

From now until the end of June is high season for rafting on the Cheat, Shenandoah, Youghiogheny, Tygart, upper Potomac and a few other wild rivers within a half-day's drive of Washington.

By fall, more than half a million people will have tackled East Coast rivers, entrusting their safety to air-filled boats and the people who drive them over waters that only a couple of decades ago were considered unsafe for boating of any sort.

How safe are they now?

Last week's adventure wound up uneventfully, and actually was exhilarating. Both boats shot smoothly through Big Nasty and Colisseum, the Cheat's other major danger spot, under the careful guidance of Stout and Kenny. With no one else on the river, it turned out to be a thoroughly satisfying wilderness experience.

But even Szilagyi admitted, once folks were safely back at Albright munching hot barbecue that afternoon, that had it been another 3 degrees colder, he would have not let the trip go off.

Szilagyi banked on eight years' experience running the Cheat to tell him when reasonable safety gives way to excessive danger, and he made a good choice.

But there have been times in the short history of commercial rafting when outfitters chose badly. One veteran river-runner from Washington remembers a day a few years back when an outfitter put a group of novices on the Shenandoah near Harpers Ferry in a flood.

"It was terrifying," said Pat Munoz, an expert kayaker who for many years coordinated river trips for the American Rivers Conservation Council. "Boats were capsizing and people were all over the river, screaming. There was nothing you could do. I was amazed no one got killed."

The potential problem with whitewater rafting is that while some states, including West Virginia, have rules for outfitters, particularly in matters of raft size and construction, guides' minimum age and training and requirements for life jackets and other safety gear, the outfitters themselves gauge the changing conditions of weather, river level and skill of their clients to determine safety of a particular trip.

This is self-regulation, and in free, private enterprise, where a fellow stands to lose a big payday if he cancels or redirects a trip, there are inherent perils to conservatism.

A couple of weeks ago, for example, Szilagyi refused to take a group down the Cheat Canyon because he thought the water level was too high. He took the group to calmer Cheat Narrows, instead, even though some of his competitors ran the canyon. "That decision is going to cost me," he said, riffling through trip evaluation cards his customers filled out at the end of the day.

The cards were critical of the decision. Customers complained they had bought a whitewater trip and got "flatwater" instead, and many said they wouldn't be back.

Will Hertig, former natural resources chief in West Virginia and now head of the 52-member Eastern Professional River Outfitters Association, said state or federal rules governing when a river was safe would be nearly impossible to fashion and harder still to enforce. The decisions, he said, should remain with outfitters.

Said Hertig, "These guys are professionals. They stand to lose too much by putting people out in dangerous conditions."

But he agreed that mistakes can be made, and said anyone taking a whitewater raft trip owes it to himself to look carefully at the outfitter, the river, the equipment and the guide, and judge for himself if everything looks right.

"There is tremendous power in these rivers," said Hertig. "It's not something to take lightly."

For a brochure on Eastern outfitters and the rivers they run, write to Hertig at E-Pro, P.O. Box 127, Barboursville, W.Va. 25504.

Locally, a good source of information on whitewater rafting is American Rivers Conservation Council, which sponsors numerous trips through the season. Write the council at 322 Fourth St. NE, Washington, D.C., 20002.