The annual lunacy on the Potomac River is starting early.

Kayaker David Hearn was paddling below Great Falls on Sunday, the first warm day of the season, when he saw a college-age crazy jump off the rocks into the 38-degree water and get swept downstream.

"For some reason he got washed back to shore. I was ready to go after him," said Hearn, who won a gold medal at the kayaking world championships in Europe last year.

The man told Hearn he jumped because two friends bet him $30 he wouldn't. "He was lucky," said Hearn. "The water is so cold it will take your breath away, but you couldn't swim in current like that anyway. Usually it takes you straight downstream. It's just about impossible to get back to shore."

A little while later Hearn was paddling on the Virginia side when he saw two girls who had made their way onto a rocky island and were trying to get back ashore. "They couldn't get across," Hearn said, "so I made a bridge with my kayak for them to step over."

Fifty-five people have died in the last 10 years on the Potomac between Great Falls and Chain Bridge, according to a recent survey conducted for the National Park Service. There will be plenty more. It's starting early this year.

Charlie Walbridge of the American Canoe Association likens city folks who run afoul of the Potomac to the proverbial bumpkin who gets fleeced when he comes to town.

"Everybody's heard of the country boy who winds up in a bad part of town and gets mugged," said Walbridge. "Great Falls is the same for city people. They don't know the dangers of nature, the power of the river. They don't know what's safe and what isn't."

For the record, the three worst places on the river near Washington are Great Falls, where the current easily can drown anyone who falls in; Little Falls, the half-mile stretch of rapids just above Chain Bridge where the river roars through a deep, narrow gorge, and Brookmont Dam a half-mile above Little Falls, where nine people drowned in a recent five-year span.

The good news is that repairs of the man-made peril, Brookmont Dam, were completed March 1, and the lethal backwash that existed just below the dam since its construction in 1958 finally has been corrected.

Hearn inspected the water below Brookmont yesterday by boat and said there is very little sign of the river-wide recirculation pool that trapped unwary boaters and became known as "the drowning machine." The Army Corps of Engineers paid $2.6 million to have the dam spillway filled with stacked bags of grout after five rafters drowned there May 5, 1984.

But even with the recirculation pool fixed, Hearn still rates Brookmont Dam dangerous. There is a steep drop on the Virginia shore, he said, and the Maryland side, while smoother, "is not easy" to navigate.

Said Hearn, "Anyone who isn't really skilled would need to be in the right place" to safely get through Brookmont in a boat, "and obviously that's a contradiction, because anyone who isn't really skilled won't be able to get to the right place."

To keep boaters from going over the dam, Maryland's Department of Natural Resources put into effect Monday a regulation banning boating within 100 yards upstream of it. It carries a $30 fine.

After all the drownings and all the warnings over the last 10 years, why do people keep getting killed on the river?

"Ignorance," said Mac Thornton, steering committeeman on the 2,500-member Canoe Cruisers Association.

"In the entire history of the CCA since 1956 we haven't had a single member drown in this stretch of river," or on any other river while boating, according to club records.

"Why?" asked Thornton. "The difference between CCA members and the 15 boaters who died in the Potomac between Great Falls and Little Falls in the last 10 years was this: The club paddlers took the trouble to be informed of basic safety rules and to know where the hazards lie.

"That's the difference between living and dying on the river."

Thornton's CCA colleague, Steve Taylor, said the survey conducted for the Park Service found that of 55 people who died on the nearby river stretch over the last decade, about one-third were "rock-hoppers" who fell into fast water and couldn't get out, another third were swimmers, and the last third were boaters, all novices who didn't know what they were getting into.

Said Taylor, "We're trying to work with the Park Service now, to get information out about where people are drowning and why. Right now, if you walk through the park and look for information on what's happening out there, you can't find it.

"Even after all that's happened, you go to a dangerous place and you can't find a sign that says, 'People drowned here!' The authorities are reluctant to post that kind of information. But it looks like that's the only thing that's going to get people's attention."

The Canoe Cruisers Association offers a variety of river and boating safety classes. For information, write education chairman John Thompson, 2221 Scotch Court, Woodbridge, Va. 22141.