Last year, at age 18, John Patrick McEnroe. Jr. became the youngest man since Jimmy Connors to be in the top 10 in the U.S. tennis rankings.

When Connors entered professional tennis at such an early age (19) it was a rarity, but today there are a host of able teen-age amateurs about to break into big-time tennis.

At the Washington Star International tennis championship this week names like Van't Hof and Iskersky were being heard in conjunction with Ashe, Connors, Ramirez and Rosewall.

"It's fantastic, what's happening now with tennis." exclaimed John Harris , cochairman of the tournament. "There are more young players breaking into tennis now them ever before.

"I think the reason is that players are being exposed (to tennis) at a younger age. There is more coverage on TV, more indoor courts, more importance now is being put on physical fitness and the prize money is getting good."

J. W. Eisenhower Jr., coach of the Junior Davis Cup team, explains the teen-age boom in tennis this way. "The guys just start out younger now. Most of these guys out here playing began at age 8 and their games mature faster as a result."

McEnroe, the best of the new players, started when he was 8.

"I got interested in the game by playing around with some friends and my dad. We (he and his father) started at the same time." McEnroe said.

McEnroe's father is an attorney who "handles me and does some investing for me."

Seeded 11th in the Star, McEnroe was the only teen-ager to advance to the third round, where he was defeated 6-7, 6-1, 7-5, by Manuel Orantes.

McEnroe is not known for accepting defeat graciously. Ever since he set a record in 1977 at Wimbledon by winning eight matches and becoming the only qualifier to reach the semifinals, he has gained a reputation of being "spoiled." In his match with Orantes he threw his racket to the ground and slammed it three times when the match reached 30-love in the second set.

As Eisenhower said recently of McEnroe, who for two years was a member of the Junior Davis Cup team, "I've known McEnroe since he was 12 and I've seen him lay down in the middle of the court and kick his feet during a match."

Spectators at the Washington Tennis Stadium for the McEnroe-Orantes match were not pulling for McEnroe. One yelled, "He's 19, the little brat."

"People in the stands watch tennis but don't really know it." said McEnroe. "You would think that the people would be for me. I am young, I am an American - Orantes is not - but it's not like that.It's really disappointing because all I am trying to do is concentrate on the court. No special shows - it's just how I react. I guess some people don't like the fact that I am young and have done well."

Sitting in a chair after his defeat and trying to postpone a prearranged interview. McEnroe didn't laugh or smile once.

Larry Gottfried, 19, a member of the Junior Davis Cup today and younger brother of Brian Gottfried, says of McEnroe. "We're good friends; I feel I can always talk to him. It does bother me though when I watch him on the court. If he does one thing wrong then the crowd gets on him."

Erick Iskersky, 20, also a Davis Cup junior, played McEnroe five times and won twice. "McEnroe is better, sure, but I don't think he strokes much better than I do. I am sure his confidence is greater. His personality is different - he's not too personable or congenial and he didn't act well when I played him." Iskersky said.

Robert Van't Hof. 19, who played two tie-breaking sets this week with Arthur Ashe, said. "McEnroe is definitely in the Connors and Ashe class now. He can be obnoxious on the court, unlike Ashe, who wouldn't pull anything."

Van't Hoff. a Junior Davis Cupper, is humble and bubbles with personality. "I pride myself on not being hung-up on my self, even though I might change if I get really good." He is ranked seventh in 18-and-under.

He has a 3.5 average at the University of Southern California but doubts he will finish his education.

"Tennis is a way of life with me. If I wait another year and a half that could kill it: Players will pass me by. Not having my education will compel me to play harder on the court. And when I am finished with tennis I will go into the management end of it (tennis)."

The amateur with the most day-to-day pressure on him is Larry Gottfried of Fort Lauderdale. His brother is world famous in tennis and was seeded second in the Star tournament.

"I guess the first time I played tennis was when I was about 4 years old," said Gottfried. "Brian was involved in the game and my folks traveled with him so it was a way of survival."

"When I entered my first tournament I was 9. But when I was about 11 I put the game to rest. It was too much pressure being Brian's brother. I wasn't good and I couldn't handle it at that time.

"I'll make my decision to turn pro within the next two years but I won't turn before I get my degree (from Trinity University in Texas). I am not wholeheartedly in tennis - I want to give a lot of things my best shot. I hate the idea of money being here longer than me."

Another member of the Junior Davis Cup team, John Sadri, attended North Carolina State on a full scholarship and says. "The only reason I went to college was to improve my game." Sadri, 21, will turn pro in September at the U.S. Open.

According to Eisenhower, Sadri, because he started playing tennis later (age 14), is one of the team's hardest workers. "Sadri has made the biggest jump of anyone I have ever seen." the coach said, "I think he will make it not only because of talent but desire."