He sits in the chair, high above the pool, sleek and aloof and vigilant. His Acme Thunderer dangles around his neck.

The whistle cord is red, resplendent against the whiteness of his muscle shirt. It matches his cap, which matches his trunks, which match the shoes he keeps in the office.

He's got the aura, the posture, the whistling technique: "Two strong hard ones," he says, twirling the whistle.

The water shimmers below him, lapping the sides, the backwash of a thousand cannon balls launched by half a thousand screeching kids. The Acme Thunderer pierces the morning air.

"Hey, buddy," he barks to a little boy standing at the deep end, peering anxiously at the bottom of the pool. "You been down here before?"

The boy bows his head and turns toward the shallow end.

Juan Carter says that if you're good, you can see the trouble before it happens, just by the way a kid looks at the water.

"If you're good," Juan Carter says, "you get to the point where you don't need to open your mouth. You just blow your whistle and wave your hand."

There are no more unequivocal heroes -- except perhaps firefighters and lifeguards. They save lives. To be a lifeguard is to be an icon for a summer. It is the perfect marriage of youth and responsibility. Up there on the chair, they are gods. They radiate power and coconut oil.

"I don't have to flaunt my authority," Carter says. "When I hit that chair, my authority is understood."

His shoulders are broad, his waist is small. He has a swimmer's body. He is 19 and the head lifeguard at the Langdon Park pool in Northeast Washington, where he has worked for the past four years. "I learned to swim here," he says. "I swam my first competitive meet here and my last competitive meet here."

It is perhaps five pool lengths from the house on King Place -- skimming distance -- where he lives with his mother and father, two sisters and niece Deonna and nephew Dante. Even from the house he keeps watch over the pool.

"He has a hard time staying away," says his girlfriend, Michelle Wallace. "He doesn't work weekends but he's always here. He has this sense of it being his pool. Everyone in the neighborhood knows Juan is the lifeguard. We'll drive by here at 3 a.m. sometimes and he has to stop to check if everything is all right, even though the night watchman is here."

She's been his girl since January 1984 -- Jan. 14, 1984, he says -- when they met at the Fort Lincoln pool, where he works in the winter. "A friend took me for swimming lessons," she says. "I had been terrified of the water. He happened to be my instructor and . . . we looked up."

"I asked her what she liked," he says, "and she said, 'The way you walked around the deck in those skimpy little shorts.' "

"Big ego," she says. "Big ego."

"You meet a lot of females," he says. "Sometimes at the end of the summer, I'll give them my whistle. I say, 'I want you to have this, sweetheart, to remember me by.' I think this one will stay with me awhile."

There are 180 summer lifeguards at the District's 44 public pools. The average age is about 17. The average wage is about $5 an hour. As a head guard, Carter earns $6.04 an hour.

"I'm not just here making the bucks," he says. "I'm an instructor. I love to dictate, be firm, be positive."

He gets to the pool every morning between 9:30 and 10. He checks the pumps and the filtration system. At 11, lessons begin. He teaches the TNS class -- terrified nonswimmers. Public swim opens at 1 with the shrill ring of a schoolyard bell and a mad dash of young bodies hurtling into the water.

"Walk!" Carter yells.

Carter had two pullouts -- "outs" -- his first year on the job, two little girls. He hasn't had to make any saves since then. Lorn Hill, the assistant manager for the D.C. aquatics program, likes to say "the dry guard is the best guard."

"Guards, we have an air," Carter says. "The way we walk, the way we talk. We're professionals."

Some nights there are adult lessons and some nights family swim, when the ladies arrive. Those are the shifts he looks forward to. "You flex, you flaunt, you swim, you impress," Carter says. "They're watching you and you're watching them. That's the fun part. It's not all hard work after all."

His mother says she is proud of him, of course, but eager to see him get into something more enduring. Last spring he completed his first semester at the University of the District of Columbia. He is thinking about majoring in law enforcement. He likes being an authority figure.

Lifeguarding has that seductive allure. There are men at D.C. pools who have been lifeguards for 20 years. "I always looked up to lifeguards," Carter says. "I respected some and envied some."

He remembers one day when he was "real small, 8 or 9, and I watched my sister Monica go off the low board here. She could swim in the shallow water but she had never gone off the board. My sister panicked and started to drown. I remember praying that that lifeguard would get her. I watched her going under and coming up, going under and coming up."

She was saved. He was mesmerized. Hill says Carter should be promoted to pool manager next summer. But he hopes Carter goes back to school. "It isn't a career, it's a job," Hill says. "Some people get stuck. You can be lulled into it, especially if you're working year round and get dependent on the income."

It is 11:15 a.m. Eight young bodies -- four boys, four girls -- cling to the side of the pool. "Okay," Carter says. "I want to see those faces in the water. Let's go. Kick and blow."

They thrash and kick and grimace, all except one little girl on the end in a shocking pink bikini who won't move off the wall. "A lot of them are terrified," Carter says. "This little girl on the end, she's terrified. Somebody must have done something to her."

He gets in the water, holding them, encouraging them. "Okay, stop!" he says. "How's that feel?"

"Terrible," a small voice says.

For the next hour, Carter cajoles, beseeches, beckons them into the water. He is gentle with some, insistent with others. The little boys splash ("Why did you do that, man?" Carter says. "Why did you splash that water?") The little girl in the pink bikini cowers. "C'mon, sweetheart," he says. "Face in the water."

She won't budge. He knows to leave her alone.

"Instructing isn't just about knowing what's in the books," he says. "It's about patience."

At the end of the lesson, he has succeeded in persuading all but the little girl in the bikini to try a "crow dive" off the wall. Sitting, chins tucked, they fall face forward into the water, reaching for him. "You better stop grabbing for me and start grabbing for the wall," he tells one girl who won't let go. Her tears blend with the 286,095 gallons in the pool.

"Okay! Playtime!"

Left alone, they forget anxiety and play until he tells them to get out. The boys run to join their friends. The girls sigh.

"He's cute, he's a champion," says Akua Hall, who is 6 and already knows how to make eyes. "I think I may marry him someday."

"I trust him," says Tiffany McDonald, who is 10. "He says he's going to hold on to you and you think he's going to let go but he don't."

"Is he important?" she is asked.

"He is when you go to drown," she says.

Lifeguards at the D.C. public pools must be 16 years old, have an Advanced Lifesaving Certificate, a CPR card and something called a "multimedia" first aid card. But Carter says, "This job here is basically public relations. To save a person's life is a necessity. But if you don't have good PR, you're in trouble."

The D.C. public pools had a total attendance last year of 900,000 visits. Admission is free. Karen Richburg, manager of the Langdon Park pool, says it averages 500 people a day, most of them between the ages of 7 and 16, and most of them regulars.

"We deal with all kinds of public," Carter says. "The majority of the guys who come here are our age. It's a hangout. If they're here every day, it means they don't have a job. That means things can get hectic. They might smoke some pot up in the park. But they don't bring drugs in the pool.

"Sometimes it's us versus them. You get some older guys who want to smoke pot on the deck. You say, 'Okay, buddy, this is how we're going to do it. I'm only going to ask you once.' You call the manager and if they can't do it, you call the police," which they haven't had to do this summer.

"It's our job to make sure the hangout is just a hangout and not their turf," he says. "A lot of people think their parents pay taxes, it's their right to swim here. It's not a right. It's a privilege."

There are pool bums and knuckleheads, little boys who live to test and torture the guards. "All these kids are testing the guards," says Audie Lucas, assistant manager of the pool. "Every day. It all comes from Day 1 when you open the pool. They know who to mess with and who not to mess with."

They line up by the diving board waiting to make their big splash. Occasionally, they glance at the man in the chair. "He is handsome and glamorous," says Marc Jones, who is 10. "But no one ever says that."

"The bullies think he's a pain in the neck," says Khalig Murtadha, 13. "One time I was in a fight here. He stopped it. The boy wanted to beat me up real bad. He was telling him, 'What do you want to fight him for, man?' He's pretty strict with the rules. He acts pretty straight."

"You're in the limelight so much," Carter says. "You're an image to them. It's monkey see, monkey do. It's just like movie stars. They got to lead their lives with a certain style. So do we. Our limitation is the swimming pool. As soon as you walk in Langdon Park, you have to portray that image and keep it at all times.

"When it's 90 degrees and 85 percent humidity and you're sitting up in the chair sweating like a dog and you're playing the same game with the regulars but you have to repeat it -- 'Hey, man why did do that?' -- that's when the vanity comes in. You're not going to have this and you're not going to have that. Just get out of my pool. When the heat gets to you, the vanity's there."

The bell sounds. The lifeguards call everyone out of the pool for the weekly antidrug lecture ordered by Mayor Marion Barry. This is standard operating procedure at every D.C. pool. But the staff at Langdon Park has taken it a bit further. Two of the guards, Carter and Rod Hill, have written a rap song to the music of Chuck Brown and the Soul Searchers' "Sure, You're Right."

The kids sit on the deck. There are posters on the locker room door: two crossed marijuana joints with the message "Just Say No" and another, a picture of a boy with his head down on his classroom desk. "The Head of the Class," it says.

"Hey, ya'll, listen up," Carter says. "I want you to sit back and listen and learn something."

One by one, the staff members take turns reciting the lyrics to the song. "If your body is strong and your will is long and you don't do drugs, just carry on!"

"Sure, you're right!" comes the kids' refrain.

"The loveboat is bad and the alcohol is sad, if you don't do none everybody will be glad!"

"Sure, you're right!"

"I want to ask you something," Carter says, ad-libbing now. "If you see a guy sitting up on the hill smoking a joint, what do you say?"

"It's bad!"

"What about you, Omar?" Carter says to a boy sitting near the back of the group.

"What you asking me for?" the boy says.

"Am I making you uncomfortable?" Carter replies.

Soon the lecture is over. The children head for the pool and Carter heads for the chair, his second push of the day. The afternoon is as long as it is hot. He glances at the sky, hoping for rain.

"When you're in the chair, your biggest audience is outside the fence," he says. "It's a good feeling. It's a good chance to impress some lady on the other side of the fence. For me, the novelty's worn off.

"At one point, I felt being in the chair was some type of role. You get up there, you get the attention and run the show. People trust you. You have a lot of people in the palm of your hand. If you sat back and thought about it, it's a scary feeling being a lifeguard."