They are 23 and 17 and can be forgiven if they sound a bit world weary at the moment. John McEnroe of the United States and Mats Wilander of Sweden, two tired tennis players, will lead their teams into the quarterfinal round of the Davis Cup beginning here Friday.

McEnroe hasn't quite caught his breath since returning from England, where he caught a cold, while losing to Jimmy Connors at Wimbledon. "Needless to say, it's not one of the greatest weeks to play Davis Cup," said McEnroe, who has played for five straight years.

Wilander, who says he does not know the word for "clone" in Swedish, has become everyone's favorite Bjorn Borg impersonator since he became the youngest player to win the French Open, beating Ivan Lendl, Vitas Gerulaitus, Jose-Luis Clerc and Guillermo Vilas.

"I don't really know much about Wilander," McEnroe said. "The first time I saw him, it was on TV at the French Open. That's the first time I ever felt old as a tennis player."

The two men, who have never met on the court, will have to wait until Sunday for their match, by which time it may a moot point. The U.S. has McEnroe and the home-court advantage--literally. "Basically, it's (the surface) that John wants to play on," said U.S. Captain Arthur Ashe.

Last year, McEnroe said it was just too difficult to make the adjustment from chilly England to muggy Flushing Meadow. So this year, the matches will be played indoors on McEnroe's kind of surface--Supreme Court. Wilander calls it "so-so," which means too slow for his clay-court liking.

In Friday's first match, McEnroe will play Anders Jarryd (for the first time ever). Jarryd, who admits to being a bit nervous, says, "He's such a good player, it's difficult for us to beat him. I just hope to make it a good match."

In the second match, Wilander will play Eliot Teltscher, who beat Wilander the only time they have met, 6-3, 6-0. Asked how he felt about playing McEnroe for the first time, Wilander said, "If he plays good, I am not looking forward to it. If Teltscher plays good, I am not looking forward to it, either."

Even if the glamour match between McEnroe and Wilander is not decisive Sunday, it may help the two separate themselves from their respective images, one as a brat, the other as a clone. McEnroe is tired but he is here (Connors is not). "I enjoy it," he said. "But it's hard. The first year or two, I enjoyed it more. I wasn't the main guy. I wasn't expected to win every match."

Wilander has a different problem. It is fashionable to say that all Swedes are Bjorn Borg clones with two-fisted backhands and lots of topspin. "None of them are clones," said Ashe. "They may play like Borg but they don't play as well as Borg."

For Wilander, the comparisons began when he won his first tournament at age 12. "Then I thought they were nice," he said. "Now, I don't care."

He was being too polite. "I don't like it," he said. "I can't do anything about it. If they should stop comparing me, the only way to not be compared is to be better. It's not easy."

Although they have practiced together, Wilander says, "I don't know him as person. As a tennis player, we're a lot different. First, he's much faster than me. You can't compare me with Borg now. He is much better. You have to compare when he was 18. Maybe I am as good as him at that age. He was much faster; maybe a little stronger. I played a little more volley. He's got a great forehand and not that good a backhand. I have a better backhand than forehand."

When Wilander returned home from the French Open, he found 40-50 reporters from all over the world waiting for him. He only talked to those from the daily papers. There have been lots of letters from lots of girls but he throws them out. This latest teen angel thinks the "others are handsomer." Indeed, he looks more like Wayne Gretzky than Bjorn Borg. So far, he says the attention has not bothered him. "It's not that much yet, but I think if I'm going on and get maybe a little bit better, at this young age, then I think it's too much."

So far, he says, the experience has not made him older than his years. "Maybe on the court," he said, "but not inside."