Cathy Hearn is the best woman whitewater paddler in the world.

She knows it, her mother knows it, her friends and colleagues in Washington's canoe and kayak racing fraternity know it. The West Germans and the East Germans and the Czechs and the British know it.

Early this month on the turbulent waters of the Aux-Sables River in Jonquiere, Quebec, she proved it. There are four women's events in world championship whitewear paddling. Hearn entered all four and when it was over she walked off with three gold medals.

It marked only the second time in the 30-year history of the competition that a woman took three golds.

Now the 21-year-old blonde is home in Garrett Park, Md., resting and recuperating from the six months of intensive training that led to her victories.

And the phone isn't exactly ringing off the hook.

It comes as no great surprise to Hearn, who concedes she began paddling with the certain knowledge that hers was not "a glory sport." But it's a little disheartening.

"I know that my winning three golds is a totally big deal," she said last weekend. She was sipping a beer at a celebration party given by the D.C. paddlers for themselves after their stunning showing at the races.

"But after I see a few more friends and get a few more congratulations, I know that'll be the end of it."

"If I lived in Austria I'd be rolling in the bucks right now. I'd have an apartment, my training and everything else would be taken care of. I'd be a national hero."

Not that Hearn is sure she'd want all the complications that go with that.

But she'd feel a lot better if she wasn't already worrying about having to scratch around for a sponsor it she wants to defend her titles at the Europa Cup races across the Atlantic next year.

She's pondering asking the West German team to sponsor her.

"I was so far ahead of everyone else that they expressed an interest in my coming over there, so they could study my training techniques," she said.

Hearn's training techniques could stand a little serious scrutiny. She pretty much made them up herself.

She runs. "An hour a day at the most," she said. She lifts weights. She does sit-ups and push-ups. She plays soccer on the women's team and the men's team at Hampshire College in Massachusetts, where she goes for an occasional semester between training bursts.

She skis cross-country. She practices gymnastics, which she taught last year for Montgomery County.

And she paddles. Twice a day, one to two hours at a time when she's gearing up for a big event.

Through it all she keeps a close check on herself, worrying about premature burnout. She felt she peaked right on time for Jonquiere.

If it all sounds informal, that's the way she wants it. Hearn and the other D.C. area paddlers credit their coach, Bill Endicott, with much of their success.

"He knows what we're like and what we do with our lives when we're not paddling," she said. "He never tells us, 'You'll do this or you'll do that . . .' He doesn't dictate to us.

"I started my training on my own when I was very young and I know I couldn't take anyone standing over my shoulder now. I'd totally rebel."

Apparently Endicott's approach works.

D.C. area racers romped at Jonquiere, Jon Lugbill of Oakton, won the men's solo canoe, Cathy's brother David was second and Bob Robison of Fairfax was third in a sweep.

That trio won the gold medal in the team solo canoe, Cathy took her three golds and there were other scattered triumphs.

It proved, in Endicott's view, that the Washington area had the best slalom racers in the world. No one disputes that.

Now if only the world would notice.

Once they did. In 1972 whitewater paddling was inclunded in the Olympics. It was the only time ever, principally because most places lack the facilities to stage the races. Washingtonian Jamie McEwan won a bronze in the races and came home a hero. His victory fueled a fire under the folks back home.

"He's was my inspiration," said Hearn, who went right to work on the Potomac. A lot of her colleagues started then, too, and they all cite McEwan's example.

There will be no Olympic whitewater events at Moscow next year, but there is a ray of hope. Endicott is working on a whitewater venue for the 1984 Olympiad in Los Angeles.

It could start a whole new breed. CAPTION: Picture, Triple gold medal winner Cathy Hearn at world championships. By James M. Thresher-The Washington Post