If ol' man river just keeps rolling along, what's to stop ol' canoe and kayak racers from doing the same?

That's what Davey Hearn wants to know. "My rule is just to keep going as long as it's fun and I'm motivated to go after it every day," says the two-time world slalom canoeing champion from Bethesda, who is 40. "It's not a proven scientific theory that a 20-year-old paddler beats a 40-year-old."

Quite the contrary. Two weeks ago Hearn beat a crowd of twentysomethings to finish first for the seventh straight year at the U.S. whitewater slalom team trials on the Ocoee River in Tennessee, site of the 1996 Olympics, in which he was the top U.S. finisher in solo canoe three years ago.

Aging can be lonely, but Hearn has that covered, too. While he was taking honors two out of three days at the trials, his sister Cathy, 41, won all three days of racing in women's kayak. The Hearns will lead a team of U.S. paddlers leaving for Europe this week to begin a summer-long series of whitewater races comprising the World Cup.

The season concludes with a World Cup final at La Seu d'Urgell, Spain, in October, which also serves as the qualifier for whitewater events at the 2000 Olympics in Sydney. The Hearns, both of whom represented the United States in the past two Olympics, hope to win at La Seu and make the Games again.

"I think it would be kind of entertaining," says Cathy. "It's all an adventure now. We're so far past what people think we should be doing, it's fun just to see what we can do."

Cathy Hearn says her attitude annoys some hard-core competitors who reckon world-class athletes must commit fully to success in order to achieve it. "They say, `You're not totally committed.' All I can say is, I'm doing everything I can to position myself to take advantage of whatever magic might present itself."

Last week the Hearns were busy doing what they've been doing for most of the past 23 years -- training on the Potomac River, usually in practice slalom gates hung in the feeder canal near C&O Canal Lock 6, a short walk from where they both live in Brookmont, which is much favored by paddlers.

Davey and his wife, Jennifer, a former member of the U.S. women's kayak team, are proud parents of the first member of the next generation of paddling Hearns, Jesse, who was born 108 days ago, a month ahead of schedule.

Cathy shares a small house near her brother's with three other paddlers, all of whom made the team for the upcoming World Cup. One is her boyfriend, Heinz Roethenmund, who will represent his native Switzerland.

Both Hearns live relatively spartan lives, getting by, in part, on grants and stipends from the U.S. Olympic Committee and some modest sponsorships. Cathy teaches and trains other paddlers; Davey has a small paddling gear company, Maximum Whitewater Performance, that outfits other racers.

If it's a lifestyle that seems more suited to a youngster, it has compensations. "If it weren't fun, I'd have gotten tired of it long ago," says Cathy. "We're constantly inventing new stuff, new moves. There's so many variables, you never take care of them all.

"I'm still improving and seeing places where I can improve. I've got a great coach [U.S. team coach Silvan Poberaj, who also lives in Brookmont]. He's a wizard. And there's a nice spirit of collaboration in our sport that's not limited by club, nationality or gender. It's good to be open and to share. That's what's made it possible for me to stay in it for so long."

Davey, who won his second world championship in 1995, when he was 36, says that rather than wearing him down, his daily 1 1/2- to 2-hour workouts on the Potomac revive him. "It's sort of a daily rejuvenation, a gathering of energy from the waters. There's never been a time I haven't felt better getting out of the boat at the end of a workout than I did getting in.

"People think it's all drudgery, but getting to go outside everyday as part of a plan or goal is a neat thing. Part of the price you pay is being habitual and dedicated enough to get your butt out on the water every day."

Davey Hearn is not so dedicated that he can't be talked into a little diversion, as I learned last week.

He was headed to his daily workout one fine spring morning, hiking down the hill from Brookmont with his race boat on his shoulder, when quite by accident I bumped into him. I was helping Melissa Andrews, another Brookmonter and former national team racer, load a canoe on her car for a downriver trip we'd arranged to make that day from Old Anglers Inn to Sycamore Island.

"Hey, Davey, want to join us?" she asked. Before you knew it, we were loading his feather-light boat on top of our clunker. He wanted to advise his wife of the change in plans, but when we stopped at the house, she had ideas of her own. She hadn't been on the river since the baby was born. "Do you mind taking a couple of passengers?" he asked.

Which is how Andrews and I came to squire the heir to the fabled Hearn paddling dynasty on his first whitewater trip down the Potomac. He was nestled securely in a Snuggly on his mother's chest and spent most of the time sleeping. He woke up hungry just before we plunged into the rapids at Stubblefield Falls and Jennifer obliged by nursing.

There's a pretty nice series of standing waves at Stubblefield and a few formidable splashes came over the bow. One whacked the nursing babe in the back of the head. He disengaged, looked around puzzled for a moment, burped, and went back to business. We saw Cathy Hearn at the takeout and told her about our adventure.

"You took my nephew on his first whitewater trip?" said the queen of U.S. women kayakers. "I salute you!"

Saluted by a Hearn. Wow!

CAPTION: Davey Hearn, 40, two-time world slalom canoeing champion from Bethesda, with wife, Jennifer, and baby, Jesse.