The Endicott house sits above the Potomac River like a boat in drydock. A two-bladed kayak paddle is mounted over the front porch. Another one is bolted to the wall just inside the door. Paintings and photographs of sailboats and canoes cover the walls. Teakwood models of ships are displayed on tables. If you are the least bit susceptible, a long visit in this house can make you seasick.

Last week, with almost a dozen of the best European whitewater racers sleeping on the floor, the Endicott home seemed even more out of place on dry land.

"We've always had people crashing here, but it's never been so international," Abigail Endicott said, trying to keep her cat Cloud from snatching the cheese and crackers set out for the visiting kayak and canoe racers. "It's like the United Nations in here."

The paddlers are in North America for international competitions this summer in Tennessee, Vermont and Canada. But they came early to see Bill Endicott and the Potomac River, where he coaches a Washington area team of paddlers who have astonished the whitewater world in the last three years.

During the last two months, American kayakers and canoeists in Europe showed again that their emergence from obscurity to best in the world was no fluke. David Hearn, 23, of Garrett Park, became the first American ever to win the Europa Cup, a three-race test of consistency. Hearn won the first two canoe races in Yugoslavia and Austria, then finished second to teammate Jon Lugbill of Fairfax in the final contest in West Germany.

In the same races the United States became the first country to sweep all three team slalom canoe races in the Europa Cup, which is one of the most prestigous series of races in the world. Kent Ford of Chevy Chase joined Hearn and Lugbill on that team.

"I can remember when I was first beaten by an American, I was very mad," said Andreas Wolffhardt, a 21-year-old Austrian kayaker staying with the Endicotts. "Now it can happen any time."

American women didn't dominate as the men did, but they brought back enough medals and cups from Europe to make customs agents suspicious. Hearn's sister Cathy, a three-time world champion kayaker, placed third in the Europa Cup and second place in the Pre-World Championship in Merano, Italy. Elizabeth Hayman of Washington, the current world champion in two-person mixed canoe, placed fourth in Merano.

America's whitewater success has intrigued the Europeans, who until 1977 regarded American paddlers as so much river flotsam. That was the year that Endicott became the U.S. coach. Now the Europeans are trekking here to see what magic this 36-year-old teacher has performed to bring the team so far and so fast.

"Their technique is better," said 23-year-old Renate Weilguny of Austria.

"The training course here is better than we have at home," said 18-year-old Franz Kremslehner of West Germany.

Last week the Europeans received a taste of both Endicott's coaching and the frothy chute of water off the Potomac below Great Falls where the Americans train. Sitting on his "throne," a natural seat of tree roots beside the fast moving water, Endicott eagerly dispensed advice to paddlers who will be competing against his team.

That kind of cooperation is more the rule than the exception among whitewater competitors. And Endicott considers it small compensation for years of help the Europeans have given Americans during annual summer trips to compete there.

"These are the people you live with most of the time," Wolffhardt said, explaining why he and other Europeans sneak food to competitors and give them rides from one event to another. "We have more friends who are paddlers than we have at home."

During seven races in 8 1/2 weeks this summer, the Americans had to navigate not only treacherous water but body-sapping travel through Germany, Austria, Switzerland, Italy and Yugoslavia. Two years ago the same schedule left many of the American racers physically sick and disoriented. This year, they handled the obstacles like seasoned veterans.

"Competing in Europe is a logistics battle more than anything else," Endicott said. "This year we had learned the ropes a little better."

"Two years ago people had accidents, lost keys to cars, a whole lot of things happened to screw things up," said Hearn, who has a face that looks too soft and fair to have spent eight years in violent water. "This time everything just worked out. We were probably treated a little differently this year too."

For the rest of the summer, it will be the Europeans' turn to scrounge food and rides, while the Americans play host. And the Americans, while doing their best to make things easy, smile when they think how the tables have turned.

"It's kind of nice," said kayaker Don Morin, "to have them sleeping on our floors for a change."