People who follow tennis know three things about Ivan Lendl: He can solve Rubik's cube in 2 1/2 minutes; he likes to play tennis on roller skates; he is a superb chess player.

"All true," says Lendl, "except the last. That is my father. He is good. In chess I am okay, but not like him."

In the last six months, tennis fans have learned one other interesting thing about Lendl. He can beat John McEnroe.

So far, Lendl is undefeated for 1982, has earned more than $350,000 in three tournaments and has soared to the No. 2 ranking in the world.

More significantly, the tall, hollow-eyed 21-year-old from Czechoslovakia has beaten No. 1 McEnroe in their last four meetings. He is, in fact, undefeated in his last 40 Grand Prix matches and in the eyes of most tennis observers it's only a matter of time before Lendl replaces the left-hander from New York as the top tennis player in the world.

"He just tears McEnroe apart," said NBC tennis commentator Bud Collins. "I don't think Mac knows what to do with him yet."

Magazines and newspapers are rushing to open the book on Lendl, who has burst upon the scene almost overnight. "His improvement in the last year is dramatic," said Collins. "He's stronger, much more confident."

Indeed, it wasn't long ago that Lendl was a gawky, gangling teen-ager trying to get out of his own way. He had a growth spurt between ages 14 and 16 when he shot up to 6-foot-2. It took the youngster years to get his elongated frame under control.

Lendl doesn't think there's anything unusual about that. "Everybody who grows has the same thing," he said last week from his U.S. home in Boca Raton, Fla. "I am physically stronger now, but it is because I have been running for the last four or five years." He runs an hour a day and practices tennis four to five hours a day, Lendl said, and that constitutes his physical training.

Evidently, it works. The last time he lost a tennis match was September, 1981, when he fell to Vitas Gerulaitis in the quarterfinals of the U.S. Open.

Since then he has won the International Championships of Madrid, the International Championships of Spain, the Swiss Indoor tournament, Fischer Grand Prix in Vienna, the Argentine and South American opens in Buenos Aires, the Volvo Masters Grand Prix in New York, the WCT Gold Coast Cup in Delray Beach, Fla., and the Molson Tennis Challenge in Toronto. He has won more than $1 million in prizes in 13 1/2 months.

The victory that most Americans remember vividly was his stunning defeat of Gerulaitis last month in the Masters Grand Prix. Lendl downed McEnroe to get to the final, then surged back from facing match point to win the last three sets over Gerulaitis.

The Masters generally is considered a notch below the four "major" tennis tournaments, the French, U.S. and Australian opens and Wimbledon, none of which Lendl has won. It is only this lack of a "major" that keeps him from the No. 1 ranking.

He regards his Masters victory as "certainly one of my most important wins." Gerulaitis, he said, "played very well and I kept saying to myself, 'Keep trying. He can't play that way the whole match.' But he almost did."

The bedrock of Lendl's game is a rocketing forehand, augmented by his hard serve. According to his friend and adviser on the pro tour, the 29-year-old Polish veteran Wojtek Fibak, Lendl today "is hitting the ball harder than anyone, and he is very aggressive from the base line."

Fibak said that in the last three or four years Lendl dramatically has improved both his backhand, "which used to be defensive," and his serve, "which is a very strong weapon."

But how did Lendl gain mastery over McEnroe?

"There is a way to beat everybody," said the young Czech, whose creditable English is one of six languages he speaks. "The key with McEnroe is to get a good return (of serve) and good passing shots. To get the good passing shots, I must make a good return. So everything really depends on the return. The last few matches, I have been returning well."

Fibak said that although Lendl "lacks the natural ability of McEnroe, he is stronger and he has a much safer base line game."

By contrast, Lendl has had no success until recently against No. 3-ranked Jimmy Connors. In Toronto this month he finally beat Connors in straight sets, 6-4, 6-3. "I hope it (the problem with Connors) is over now," he said.

While Lendl's talent on the court is undisputed, his social success has been less sweeping. The young Czechoslovakian has a reputation for being aloof and occasionally condescending to American media and the public. On the court, his fierce competitiveness sometimes puts him in shouting matches with opponents and officials. A photo from the Toronto tournament Feb. 2-7 has him gesturing obscenely at an official.

Close associates say it's partly an act. "He is serious on the court because that's the right way to play," said Fibak. "Off the court, with people he likes and admires, he's the nicest guy you can imagine. But he's still a very private person."

Said Collins, "Really, I think he's a pretty nice kid. He puts on an act, as if he's very stern. I think he was burned a couple of times early on by the press. He told me, 'They didn't speak Czech and I didn't speak English.'

"He looks so stiff and stern, but he's not that way at all. He just wants the public and his opponents to see him that way."

Lendl, the son of a lawyer, grew up in the industrial city of Ostrava. Both parents were top tennis players in their time and he was playing paddle tennis when he was 3 years old.

"I was always playing on some team," he said. From age 8 to 17 he spent his summers playing tournaments--16 of them every year. It was perfect training for the pro tour, he said, because it involved 160 matches over eight weeks against the best competition of his age group in the nation.

Fibak said Lendl is uncomfortable talking about his personal life; that he worries about "what he can say and what he can't" without angering Czech officials, at whose pleasure he roams the world. But according to Fibak, Lendl likes America and Americans "more than he can say. He likes the country because it's so organized and he likes the American people because they are so direct and friendly."

Lendl is quite straightforward about that. "I like the easy life and that's what you have here," he said. "You get out of an airport and you do what you want. No money to change. The telephones, hotels, rent-a-cars. It's all so simple. It's nice, with all the complications of life, that I don't have to worry about the little things."

And of Americans, he said, "I like that they say what is on their minds. If you say, 'I don't want to do business with you because I don't like you,' I say, 'Good, goodbye.' It drives me crazy when people are indirect."

For a fact, there's nothing indirect about Lendl's heading in tennis these days.

Straight up. CAPTION: Picture, Ivan Lendl has not lost a match this year and has won more than $350,000. He credits running for part of his recent surge. UPI