The Potomac River glides over the two-foot lip of Little Falls Dam as smooth and slow as honey, raising a white water chop that doesn't look too difficult to canoeists fresh from the turbulent chutes upstream.

A closer look reveals a collection of tires, styrofoam and sundry flotsam that thrash and bob in perpetual motion, seemingly immune to the general direction of the river. Logs shoot out of the tumbling water like salmon, headed back up stream.

Local rescue workers know this deceptive stretch of water, which flows two miles upstream from Chain Bridge, as "the drowning machine."

It has, in the last five years, claimed eight lives, according to firemen at Glen Echo. Saturday evening, two Navy seamen nearing the end of a day's outing were dragged under and both were presumed drowned. Searchers recovered a man's body from the river near Fletcher's Boathouse downstream from the dam last night, but refused to say whether it was one of the seamen pending notification of relatives.

"If you're planning to paddle across it, you should have a rescue team standing by," says Ken Fassler, a 49-year-old paddler who has himself been trapped in the swirling current. "That's a dam designed to kill people."

The 1,500-foot stretch of concrete also known as the Brookmont dam spans the Potomac. It was constructed in 1958 to divert water into the Little Falls pumping station to augment the Washington area's drinking water supply and is 100 yards above an increasingly porous structure called the Old Rubble dam, built in the 19th century to shunt water into the C&O Canal.

Although 14 feet high, water sweeps over the top of the Brookmont dam, dropping one to two feet, depending on the height of the river, and then sliding down a concrete incline. The water circulates back over itself, creating what is known as a "hydraulic" that pins tree trunks in midstream for weeks and even months. Although the dam and the white water below it look relatively easy next to some of the rapids that canoeists and raftsmen run upstream, the tumbling current is extremely hazardous.

Some people have been pulled to safety with ropes, and, in one extraordinary instance, with 12 1/2-pound-test fishing line, according to Park Ranger Rod Suarez.

But Lt. Richard Arnold of the Cabin John Fire Department maintains that "the water is too bad to put any rescue workers in that area" and a helicopter is required for rescue.

The four seamen who set out on a weekend lark to navigate from Great Falls to Georgetown in two rented aluminum canoes were all stationed at the Navy Security Station in the District of Columbia. They had never been down the river before, but they knew of the danger of the dam and planned to portage around it, according to one of the survivors, George Henry Graas, 20.

Graas was paddling with 18-year-old Anthony Cangilaosi; Carl Cheskey, 20, was joined by Mark A. Bucks, whose age was unavailable. Cangilaosi and Bucks drowned.

Around 6:30 p.m. they passed the red and white buoys that warn of the dam.

Cheskey and Bucks were abour 10 feet away from the concrete pump house. "We got over and some kind of undertow pulled us in and rolled us over," Cheskey recalled.

Cheskey clutched a cooler and Bucks held on to the overturned canoe as the water buffeted them.

Meanwhile, Cangilaosi and Graas scrambled ashore. Seeing his friends' distress, Cangilaosi ran around the pump station, climbed over a concrete retaining wall below the dam and headed into the water.

"Anthony wasn't using his head," said Cheskey. "We yelled 'Stay outta here!' He tried to rescue us. He hooked onto the canoe. I was facing the pump station. When I looked, the other two were gone."

Graas was able to throw a rope to Cheskey floating on the cooler and Cheskey struggled ashore.

Rescue workers arrived from the Glen Echo Fire Department shortly after 7 o'clock, and a helicopter hovered above the damsite searching for Bucks and Cangilaosi. Until darkness forced searchers to halt around 8 p.m., they saw nothing more than the seamen's empty canoe twisting and rolling in the river.