When they slept, mosquitoes and black flies bounced off their tents like rain. They lunched at a sun that never set and ate dessert with hot chocolate at 3 a.m.

White wolves watched them from the river's edge. Arctic terns swooped overhead.

Cecilia Van Hollen, 16, almost didn't make it back to her home in McLean to tell these tales.

Along with five friends and a teacher from the Potomac School in McLean, Van Hollen took a 51-day odyssey this summer through the Northwest Territories of Canada and across the Arctic Circle, 4,000 miles from home.

But even before they reached their preliminary destination at the headwaters of the Coppermine River, Van Hollen got a taste of terror.

The color left her flushed cheeks as she recounted the story on a recent evening in the home of her classmate, 16-year-old Kathy Rankin of the District, who also took the trip.

From Washington, the group, which included four Canadians, had driven to Yellowknife, capital of the Northwest Territories on the northern edge of Great Slave Lake. From there, the 10 travelers flew about 180 miles north-northeast by seaplane, and put their five canoes into Lac de Gras, the first of five interlocking lakes leading to the raging white waters of the Coppermine River. Their ultimate destination was the Eskimo village of Coppermine, about 110 miles above the Arctic Circle.

Van Hollen's brush with terror occurred six days into the 27-day canoe trip. The sun was bright that morning, warming the tundra and the travelers. At breakfast, they had spotted their first caribou.

After they had packed their gear, the group scouted the day's trip. Between Lake Providence and Point Lake, the third and fourth lakes on the way to the Coppermine River, the water narrowed into a three-tiered set of roiling rapids: It is called Obstruction Rapids.

The first three canoes made it through to the flat water of Point Lake. Van Hollen was in last canoe with James W. (Skeeter) Lee, 29, the Potomac School history teacher who organized and guided the trip.

Van Hollen and Lee watched the fourth canoe maneuver the first set of rapids, take water and flip as it reached the middle rapids. By then, Van Hollen and Lee were among the rocks, and waves were washing over the gunwales of their canoe. The water was about 45 degrees, cold enough to render someone unconscious after 10 minutes.

"We started to take water, and it was hard to maneuver," Van Hollen recalled. "I started to panic. We hit a rock and flipped."

Lee was able to swim ashore, but Van Hollen was swept downstream, shooting by rocks, her head kept above water by her life jacket. Another canoe pulled alongside and she grabbed the side, but the force of the water broke her grip.

"It was an incredible pain to breathe," she said. "I was terrified. I knew if I hit the next set of rapids, I could easily be gone.

"Finally, I bumped into a big rock that hit me in the butt and flipped me into the air," she said, "and I was able to make it to shore."

Luckily, little was lost and no one was hurt. Canoes, paddles, packs and food floated undamaged into Point Lake. Van Hollen, Lee and their two compatriots shivered dry in the sun, ate and were back on the water within an hour. It was the most harrowing experience of the trip.

"It jolted us a lot," said Van Hollen. "It was our first realization of potential danger."

Last winter when the teen-agers were planning the trip, their parents knew it could be dangerous. Although this was the fourth camping and canoeing trip for Lee and the Potomac students, it was the most ambitious.

Isolation was a major concern. At the point of Van Hollen's dunk in the icy waters, the group was about 300 miles, by water or air, from the nearest town.

"It's wilderness up there," said Douglas Rankin, a geologist who took his family camping in the Sierra Nevada when his daughter Kathy was only 5. "In theory, I was excited about the concept, but in practice, I was just concerned about safety. It took plenty of soul searching to let Kathy go. It came down to my faith in Skeeter."

Skeeter Lee, a wiry blond with a beard and moustache that almost hides his mouth, has been leading such trips for three years. His enthusiasm for the wilderness is so intense that teaching seems to be a sideline to the summer treks.

Lee had taken Van Hollen, Rankin and three other Potomac students -- Romey Pittman, 15, of the District, James Peabody, 17, of New Hampshire, and Bradford (Skippy) Norman, 16, of the District-- on other, shorter wilderness trips. Last summer it was the Dumoine River in Quebec for two weeks. Since this was the students' last year at Potomac, he proposed the 51-day trip down the Coppermine River.

Preparation began when school opened last fall. Lee read the 600-page journal by British explorer Sir John Franklin, the first white man to run the Coppermine in 1821. Between Franklin's trip and 1970, no more than 200 whites had been up the river, according to Lee. Now an average of 15 groups a year travel its twists and turns.

While Sir John's log was helpful, Lee got more current information from a travel agency specializing in Arctic expeditions and from friends who had made the trip.

The students sought sponsors but found few. They estimated the cost at nearly $1,500 per person; the actual cost was $1,300, according to Lee. Although National Geographic donated color film and processing, and local merchants gave the group discounts on equipment, the students and their parents paid for the trip.

On July 5, Lee's black Dodge van was loaded with 10 people and all their equipment including light-weight tents, dried trail rations, sleeping bags, backpacks, fishing poles and a headdress of five 17-foot canoes. Fourteen days and 3,500 miles later the group arrived in Yellowknife.

From Yellowknife, a town of 12,000 enjoying a boom from oil and uranium exploration, the crew made their last phone calls home. Then with the dusty road and civilization behind, they flew in a twin-engine Otter to Lac de Gras. The plane plopped them down on the water, literally in the middle of nowhere.

"It was a shock," said Rankin. "It looked so barren and desolate, but we found so much life there."

"It wasn't a lonely feeling," said Van Hollen, "but one of being alone."

"And insignificant," added Rankin.

"In many ways it was a very comforting starkness," said Lee.

The colors were the muted green and gray of rocks against blue water and an occasional burnt orange from a patch of lichen. Moose fed along the lakes and river. A small grizzly bear swam across the bow of one canoe. Caribou were abundant. Eagles rode the wind.

They saw three people -- a group of Germans -- in three weeks.

Information about fishing had been conflicting. Some said bring equipment, others said not to bother because there were few fish.

On the second day out, Peabody and Norman caught a 20-pound trout, which they cut into inch-thick filets and feasted on for two days. Later, they caught their fill of Arctic char and graylings.

Since the sun never sunk below the horizon and darkness never settled on the tundra, the crew was free to arrange its days without concern for darkness. The days were windy and buggy, so they slept. The nights were calm and cool, so they paddled, an average of 20 miles a day.

"We weren't living by the clock anymore, we were living by the weather," said Rankin.

After paddling the series of five lakes, the crew reached the Coppermine River that snaked about 250 miles north until it spilled over Bloody Falls into Richardson Bay at the village of Coppermine. The banks of the river began to rise steeply as they dropped out of the tundra. Spruce trees, standing solitary rather than clumped into forests, began appearing.

Finally, the land flattened into sand banks. The travelers saw Eskimos fishing in small camps or running upriver in motorboats. It was Aug. 15, their next to last day on the water.

"People went off in different directions to walk or write in their journals because it was our last chance to appreciate the Arctic wilderness alone. . . . It was a very awkward and straining feeling for everyone to think of ending the trip," the students wrote in the common log book.

The village of Coppermine and its 800 inhabitants welcomed the 10 Americans and Canadians as celebrities. The group had written ahead and their penpals showed them the town.

In their two-day stay, they saw some events in the Northern Games, an annual Eskimo competition of skill, strength and endurance. Then they flew back to Yellowknife and began the long drive home.

Rankin is now at National Cathedral School, Van Hollen is going to Sidwell Friends and Lee is teaching another group of students at Potomac School. The rest of their companions are in boarding school or back home in Canada. The Arctic Circle seems far away.

But the memories are vivid.

"Looking back, it was pure enjoyment," said Rankin.

"It was just as much learning as enjoyment," said Van Hollen. "But I'm not sure I'd do the same kind of trip next summer."

"I'd go again tomorrow, take the same group and spend the same amount of money," said Lee.

"I guess I'd go, too," said Van Hollen.