Police divers in the Potomac River yesterday recovered the body of an Alexandria man who disappeared in a lagoon Saturday after choppy water swamped his flat-bottom boat.

U.S. Park Police identified the man as Ernest Cook, 54, of the Lynhaven section of Alexandria. Cook and a friend were fishing in Roaches Run, a waterfowl sanctuary near National Airport, when wind-driven water poured over the sides of their boat, police said.

Neither man was wearing a life preserver when the accident occurred. Lt. Kenneth Ford of the Metropolitan Washington Airports Authority said that a life preserver might have saved Cook's life.

Experts said yesterday that while accidents on any body of water are bound to happen, boaters or swimmers usually can avoid serious injury or drowning by following a few simple rules.

"Stay calm," said John Malatak, of the American Red Cross. A little thought can often help avoid serious danger, he said. "Stop, think and act," he said. "You want to relax and think."

Malatak said people in trouble should try to remain near a foundering boat, and use it for support and visibility. Don't automatically try to get to shore, he said.

Try to remove heavy clothing and shoes, which can make swimming awkward, Malatak said. A closed shirt, however, can become a floatation device if the wearer grips the neckline to hold in air. More air can be blown in through the front opening as well. {See illustration.}

Trousers also can be taken off and used as floats, but it takes a good swimmer and some practice to make them work, he said. People in trouble should always try to yell for help, he said.

"A lot of people are inhibited and don't want to admit needing help," he said, adding that most accidents involve men 17 to 25 years old.

There are other techniques for survival, but Malatak and others say the best way to prevent drownings is to plan ahead.

Larry Pinkney, an area Boy Scouts of America official, said the most important rule is to wear a life preserver. "That's the biggest safety device right there at your fingertips," said Pinkney, the commissioner of the Scouts' Benjamin F. Banneker District and a counselor for the Boy Scouts' swimming merit badge, which includes basic water safety.

Trying to anticipate what to do in an emergency can help people stay calm when a sudden storm or unexpected wave fills a boat with water. Malatak also advises checking the weather before any excursion.

The Red Cross recommends that every boater take a water safety course and learn to be more cautious than circumstances seem to dictate, Malatek said.

"Always exercise common sense where you're around water and never overestimate your ability," he said. "When in doubt, don't."

Respect for any river or lake is important, he said. Cross currents beneath the placid surface of the Potomac, for example, can pull even the strongest swimmer underwater, Malatak said.

The problem becomes more acute in colder water, he said.

If you ever fall overboard from a boat far from shore, your clothing can be used for supporting you at the surface until assistance arrives.

Experts recommend removing shoes.

If you jump into the water wearing a cotton shirt or other closely woven material (not wool), grip it tightly at the neck. The air trapped in its back and shoulders will keep you afloat for a time.

More air can be blown in through the front opening between the second and third buttons. Just bend your head down, pull the shirt opening to your mouth and blow air into the shirt. It will move to the back and form the supporting bubble.

It helps to have your collar button fastened and your shirttail tucked in.

SOURCE: Excerpted from Boy Scouts of America Merit Badge Series. Swimming