The D.C. National Bank Tennis Classic separates the dilettantes from the true believers.

For the volunteers who work the tournament, it's an annual ritual of marathon labor during heat-blasted dog days with no salary but the pleasures of the game. You have to think tennis is more than adult ping-pong to do it.

"They work anywhere from six to nine hours out there" on the griddle-like clay courts, says Pat Jenkins of the ball boys she supervises. "Some of them are here 12 hours."

"People just crazy about tennis are the ones that come out," says Dwight Mosley, executive director of the Washington Area Tennis Patron Foundation. "And these volunteers come back year after year."

The organization will supervise an estimated 800 volunteer drivers, ushers, security people, ball boys and other youth this year for the tournament, which ends Monday. It also provides free housing and hospitality for the players.

The voluntary aspect of tennis is par for the court. No sport around is so dependent on a labor force of good will. It's another year, another freebie with every tournament, and the local volunteers never seem to get enough. Some have shown up every year since the tournament began as The Washington Star International tennis tournament in 1969.

The links between the tennis-support community and the game are manifold. Most volunteers have a friend or family member playing in some kind of tennis circuit. Others hold quiet tennis ambitions of their own. All of them love tennis and, for many of these racquet-and-ball addicts, driving Yannick Noah to the zoo, or throwing tennis balls to a sweating Jimmy Connors, is psychic income enough. It's not so much a Feed-the-World voluntary spirit as it is The Joy of Tennis.

"I've done it for seven summers," says Debbi Clark, a 20-year-old American University student whose job it is to chauffeur the players around. "I love to play tennis and I love to get to know the players. Most of them are really friendly. Some are outgoing, some are on the quiet side and want to be left alone with the radio.

"I drove [Jose'-Luis] Clerc last night," she says. She rolls her eyes when asked about her recent client. "No comment," she says.

"Debbi, can you go to the Shoreham?" asks Carpenter. "Clerc needs a ride."

"Jose'-Luis Clerc is my favorite," says 15-year-old ball boy Robert Spalding. "He's real nice. It's neat to talk with the players. I've talked to [Andres] Gomez and [Ivan] Lendl."

On a weekday morning at the tennis grounds at 16th and Kennedy streets NW, the sun is getting ready to do its steamy damage. Under a mini-marquee, ball boys and ball girls gather before the scheduled tennis matches to find out their schedules for the day. The smaller ones will probably find themselves kneeling at the net all day, the others at the back of the court. Some might work a small qualifier match on a side court, others might get Harold Solomon in the center.

Inside the transportation trailer nearby, the day is already cooking. The phone rings frequently and below a window festooned with notices giving names and addresses of players and drivers, Bea Carpenter fields calls and hands assignments to incoming volunteer drivers. A tennis player waits in the trailer to be taken downtown. Another calls from the Shoreham. Someone needs to be picked up at a private home.

"We take them anywhere they want to go," says Carpenter. She is straightening out the latest snafu. A player was late for his pickup and his driver, ferrying another player hot for the courts, had to leave him behind. The tardy tennis player is calling in to find out what happened. Carpenter, tanned and positive, consoles the caller and puts down the phone.

The drivers "show up here at 8 in the morning," she says. "And they stay until 11 or 12 at night. It's crazy, but they do it . . . Many are college students. One guy owns his own business and gives a couple of days a week."

A young man in T-shirt and tennis shorts comes into the office. "Hey Raymond, got a run for you," says Carpenter. Raymond's sweating face and lack of response speak volumes.

"Now Raymond," says Bea with a motherly there-there. "Grab an apple."

"It's fun, you meet a lot of people," says Raymond Wilson, a 20-year-old University of Maryland student with tournament ambitions of his own. "One day I'll be out there."

Ball boys Robert Spalding and Steve Montgomery wait listlessly in the shaded heat for their next game.

"We'll do a match," says Spalding, who sports a blond punk cockatoo hairstyle. "We'll wait a while, do another. We do about three or four matches a day. It gets hot, you take a break. You get a drink of water."

"We used to like tennis a whole lot," says Montgomery, a ball boy in his sunset years at 16. "But we've kinda grown out of it. There's other interests I guess."

Like what?

"Girls and rock 'n' roll," says Spalding.

"There are some kids whose lives are totally dependent on tennis. They're 10, 11 years old. By the time they're 13, they're playing circuits. Those are the kids that become the pros.

"I'm not good enough," he says with resignation.

The ball boys say they get little appreciation from the players. In the Grand Champions tournament (which ran just before the D.C. National Bank event), players were all over 35, and "more relaxed," says Montgomery. "The younger players are a little tense, always yelling and screaming."

"Some people like their towels unfolded. You can't give it to them folded up," says Spalding.

"You got to watch the player's face," says Montgomery. "He'll nod if he needs the towel . One guy . . . came up to me and said, 'I don't want to keep on telling you when I want a towel!' "

Ball girl Jane Cohen, 15, waits nearby, with the air of a model student waiting for math class.

"This is my third year," she says. "I'm a net person because I'm short. I don't mind it, the net people get to take care of the players . . .

"My family's a tennis family. My grandmother started the tournament when it was with The [Washington] Star. She ran the ushers, the ball people, the court crews. My uncle was head of the wheelchair tournament. My father was on the court crew here. My aunt was an usher. There's another uncle. My sister [Mia] is a ball girl . . . My dad played with Harold Solomon at the Indian Springs Country Club."

"For 10 days I don't get anything done at home," says Gladys Austin, who has volunteered for various tournament committees for 15 years. This year she chairs the players' hospitality committee, facilitating guest passes, parking tickets, entertainment, and long-distance calls for the players. Her three children have all volunteered for the tournament over the years, her son Sean is ranked 67th with the U.S. Tennis Association and "my daughter married a tennis guy."

"It isn't easy with the heat and everything," she says. "You have to like tennis. But I look forward to this tournament every year. You get an empty feeling when they pull down that site."