Players are not the only ones eliminated in a tennis tournament. So are ball person.

With each succeeding round of the Washington Star International at 16th and Kennedy Streets NW, ball collection coordinator Barbara Bath is faced with the unhappy task of informing some of her young charges that their services will not be required the next day. So how does she give the word? Very carefully. "I write it on a sheet of paper and I put it on the table in the ball boys' tent," said Bath, lapsing into outdate sexist terminology for the moment, "and then I run and hide."

Actually, very few of the ball persons give her any guff, says Bath. But parents are another matter. They are constantly homing in on Bath, demanding to know why their children have been cut.

"Some of the parents get more vicarious pleasure out of seeing their kids than their kids do (in performing their duties)," said Bath.

With ball persons as with players, performance determines who moves ahead and into the next round and who has to pack up and head for home. Bath and her sons David and T. Jay constantly, wander) from match to match with eyes peeled for any ball person who seems to be tiring, or choking, or making a lot of unforced errors.

Larry Rassin, 12, of Potomac, has ball-boyed for five consecutive Star tournaments but has never made it all the way to the finals.

You've got to be pretty good to make the finals," said Rassin, who kills time between his matches playing "hand tennis" on the sidewalk and collecting players' autograps (he already has gotten Jimmy Connors' twice).

"We get T-shirts, Cokes after the matches, we get to watch the matches, and we ket to meet the players," Rich Freeman, 13, of Chevy Chase, itemizing a ball person's compensation. And what does a player say to a ball person? "(Harold) Solomon asked me if I was feeling good or something," said Freeman.

The ball persons' biggest grievance this year is that they are apparently not going to get to see Sunday night's final - that is, except for those who are on the court picking up the balls. Last year, the ball persons sat on two rugs alongside the center court.

There will be no room for them this year, they have been told, because the final will be broadcast on commercial TV - not public TV, as in the past - and the cameras have to be able to pick up the advertisements on the sidecourt fence.

Before the start of scheduled play yesterday Arthur Ashe and Willis Thomas, the pro at the Skyline Racquet and Health Club. Baileys Crossroads, played an exhibition doubles match against Chile's Jaime Fillol and another local club player.

"That's the first time Arthur and I have been on the court together since about 20 years ago" said Thomas. "We played doubles when we were 12-to 15-year-olds. . . There wasn't much professional tennis, especially not for blacks unless you were one of the top players. I guess Arthur just had that instinct to keep on until you get to the top. I guess he was a little gamer than I was."

"I'm not interested in tennis," said Butch Smoyer, who has been the head electrician at the tournament since 1976. "I watch them bat the balls around but I don't care about it . . . I'm more or less a football fan - football, baseball."

A few years ago, Smoyer said, he did the wiring for a special gala at Larry Brown's restaurant, and Brown promised him a free football if he worked overtime. "I stayed there 6 1/2 hours of overtime, and I never did get that football," said Smoyer bitterly.

Through most of 35-year-old Ashe's match against 19-year-old Robert Van't Hof, the crowd was quiet and reduced to mutters of discontent with the older player's game.

"Sloppy!" said one critical fan of an Ashe forehand that puts him behind, 1-4, in the first set.

"Three years ago he wouldn't have missed that volley," said another, as he watched.

"I don't want to watch anymore," added a third. but a moment later there was a cry of "All right!" as Ashe put the finishing touch on an elegantly played point and then claimed a third game to Van't Hof's five.

"The "All right!" came from Bob Peabody, a professor of political science at Johns Hopkins University.

"What I look for is kind of unusual competition," said Peabody. "This is a good example where you have a young player playing a guy who is on his way down."

"Game to Ashe," said the umpire. "Games are 5-all, first set."

"How about that," responded Peabody.

Hank Finelle of Falls Church, who drives a laundry truck for a living, has tickets to every session of the tournament from start to finish.

"I know his feet aren't too good, but he can move better than that," said Finelle, offering a post-mortem on another point lost by Ashe. "Still using that Comp II, huh? Hey! That was out! Bad call!"

"You know, I can't understand these linesmen," said Carol Booth, a housewife from Arlington. "As much money as goes into a game like this, why can't they have an electronic device to call the lines?"

The first-set tie breaker has gone to Ashe, 7 points to 3, and Betsy Heidenberger, who hopes to be ranked third or fourth this year among the Middle Atlantic Lawn Tennis Association's 18-and-unders, says comments:

"When Ashe was down all these set points, he really kept the pressure on. He played even tougher when he had to. That's interesting."

Nancy Bynon, sitting with Heidenberger, has been considering another aspect of thr tournament. "Why can't we make hot dogs like this at home?" she wants to know.

Beaver Cohen is in charge of supplies, which means tennis balls, soft drinks, cups, coolers and, above all, towels. Last year the tournament was accused of losing more than 1,700 towels, and Cohen is determined not to let it happen again, although, he said "It's questionable whether we lost them or whether the towel company has a strange way of counting them."

In any case, towel losses have been cut dramatically this year. So far, said Cohen, "we've only lost 10. If we keep up the way we're going, we'll think we'll lose that many because we're keeping such good count. Right now I know where every towel is."

A tournament official burst into the supply trailer to inform Cohen of a distracting banner that must be removed from one of the grandstand courts, and as Cohen headed for the scene of the crime, he observed wearily, "It seems like when something has to get they come to me."