Washington tennis fans either are the most knowledgeable in the country or the most gullible. For nearly a week now, they have flocked to the Star tournament to watch more unknowns than Carter's new Cabinet. Or the Redskin special teams.

Like the Redskins, the Star tournament is appealing almost as much as a social occasion as for exquisite tennis, the sort of event that prospers with one Guillermo Vilas and 14 Eliot Teltschers when the other corporations in short pants - Borg and Connors, Tanner, Gerulaitis and McEnore - are chashing dollars elsewhere.

Eleven years ago, when the tournament began, few believed the area would support an avent that included every in-his-prime player who ever stroked a passing shot. Now there are enough free-spending hackers to give the sport's future elite a coming-out party - and themselves a chance to scan the crowd for the political hib servers and a David Schoumacher preening.

Every sport has its passionate core, fans as much interested in catching a future star on the rise as a present one in orbit, Basket- ball, junkies will go hundreds of miles to see the next Dr. J. serving his internship in an obscure playground. Dedicated duffers stalk junior-tournament fairways in hopes of seeing the next Nicklaus before anyone else.

Those who tall young runners and jumpers are the most honest, openly calling themselves "TaFnuts (track and field nuts)." Several years ago, they were certain the world would one day celebrate a sleek, teen-aged rocket being quietly launched in New Jersey, Renaldo Nehemiah.

Grass-roots tennis got its Orthogrow about the time John Harris and Donald Dell decided to plan a tournament for Washington. That same wild, at times unchecked, growth has given fans this week a crop of new players worth waiting until midnight to see.

"It's getting to the point where-tennis is pretty deep," Harris said. "All of the programs for youngsters, the sport's explosion, the money have produced all these great young players. And McEnroe's the first of the big group.

"Whether this one will be find as the croup Connors was in remains to be seen. That one include (Roscoe) Tanner and (Brian) Gottfried and (Radl) Ramirez and (Dick) Stockton and (Eddie) Dibbs.

"They all played against each other for years. Dibbs once beat connors in one of our satellite events here eyears ago, on one of the back courts.. Of that group, I guess Stockton was the best growning up, before his back problems."

This year, three Junior Davis Cup players - Fitz Buehning, Mel Purcell and Robert Van't Hof - made it past the first round of the Star tournament. Victor Pecci and Jose-Luis Clerc advanced to the semifinals where Pecci upset Dibbs.

Teltscher is 20 and not quite as tightly strung as his rackets, although he seems to put at least as much pressure on himself as outsiders, a 14-pounder with as much power on his backhand as you would expect from Ken Singleton stepping into the ball.

"Never saw a guy hit so many winners (off his backhand)," said Dibbs, after he managed to use a combination of his own 28-year-old wile and stamina and Teltscher's inexperience to rally from a one-set, foru-games-to-three deficit and win that quarterfinal match.

Teltscher seems to have a fine tactical sense, or he did in the first-set victory over Dibbs, and the sort of occasional backhand that knocks opponents' rackets into the stands. But instead of being pleased to have played quite well against a splendid claycourt player, Teltscher chose to spank himself. And a whole lot of grownups let him get way with it.

Before the match, he had looked at his life and said: "The reason I turned pro (after a year at UCLA) was that I thought I could do well. I had passed up my last year as a junior to play in pro qualifiers-and I did well.

"A lot of guys are jumping in too quickly, I think. They see all the money and they want to get into it. But they get out here and they're having it tough having to play in qualifiers week after week.

"I haven't had to do that since I've been on tour. I think you should be awfully sure of yourself before you drop out of college."

Later, he was as depressed as he had been hopeful. The pressures to succeed have been so great for so long that he appeared a confused and lonely child, racing to master a sport now dominated by a man just threes year his elder, Borg.

It did not help that traditional jaundice and tight deading made postmatch reporters anxious to get to the critical point of the match with Dibbs instead of guiding through the immesely positive part early in the interview."

Had he choked?

"I choked," he said - and the self-flagellation began in earnest. "On the big points, I was a tentative as could be . . . I've lost many a lead . . . It's become a habit . . . I don't feel tired (but) I'm not concentrating. I'm so nervous my hands start shaking.

"I've got to get the first serve in, because I'm scared . . ."

Surely, this is a phase part of maturing as a pro, like a young Tom Watson having to endure losing final-round leads before growing tough enough and developing the stroke - and the will - to win.

"I've done this since I was 12, it hasn't changed since, so I see no reason for it to change in the next eight years. I just don't think. I lost my sense of what's going on."

Also, Teltscher is lonely and out of sorts because he feels McEnroe - to the exclusion of other fine young players - gets all the public attention.

Teltscher growled and almost cried. He talked about language problems in France, how, he had time just to grab a beer or two and a few hours sleep before catching an early morning flight to the next torunament.

Every so often came the strong urge to yell, "Grow up." But then there is no time for that. There never has been.