They are a study in contrasts: Ivan Lendl, the Czechoslovakian who has never won a Grand Slam tournament title, and Martina Navratilova, the former Czechoslovakian who has won every Grand Slam title but the U.S. Open in the last 12 months.

On the court, he is as passionless as she is passionate. He stays in the back court, never giving himself away emotionally or tactically. She comes to the net, holding little of herself back.

Navratilova, who defected to the U.S. in 1975 and became a U.S. citizen last summer, embraced America -- junk food and the Dallas Cowboys. Forget the fact that this year's Open, which begins Tuesday, would be the third leg (or fourth, depending on how tennis decides to interpret the changed date of the Australian Open) of the Grand Slam. Forget that she will receive an additional $500,000 for winning the Playtex Challenge Series. She wants fervently to win the Open because it is her country's title.

Although Lendl did not know her as a child, Navratilova has had a significant impact on his life. "The defection of Martina has really changed dramatically the way the Czech government deals with players," Donald Dell, Lendl's attorney, said recently. "He was 14 or 15 when Martina defected. It had a tremendous impact. He didn't know if he could travel. The whole coaching system has loosened up."

But Lendl has not -- partly because of incessant questions by those who wonder if he will follow in Navratilova's footsteps. Now, there are other questions, apolitical ones, he must answer. Although his match record since last year's Open is 117-6 (including a 44-match streak) and he has won 10 titles, including the Volvo Masters, the closest he has come to winning a Grand Slam event was a loss to Bjorn Borg in the final of the 1981 French Open. This year, he skipped Wimbledon, claiming he was allergic to grass.

Last year, when Navratilova lost the Open final to Tracy Austin, after leading by a set, the crowd at Flushing Meadows gave her a standing ovation, and she cried. "She was just so emotional, it was neat," Austin said. "It was fabulous they were saying to Martina, 'You did great, we still love you.' I'm sure it helped her to be more accepted."

Who is to say how much that gesture of acceptance has had to do with Navratilova's phenomenal year? She has lost one match so far in 1982, to Sylvia Hanika in the final of the Avon Championships, and one coach, Renee Richards, who quit to resume her ophthalmology practice full time. It remains to be seen whether this coaching defection will have an effect on Navratilova's tactics.

She has won everything else: 64 matches, 13 tournaments, including her third Wimbledon. She is playing the tennis everyone always expected of her, exhibiting elan, grace, confidence. "Martina is going to be confident," Austin said. "Going off her record, she is certainly the dominant force."

Austin is seeded third in the tournament despite a lamentable year. "I got burned (by coffee), had my back and the stomach flu twice," she said. She has played in only six tournaments this year, and only one since Wimbledon (San Diego, her only tournament victory of 1982). "I'm playing well. I'm eager, I'm healthy," she said. "It's just a question of whether it's enough matches."

A victory could salvage an otherwise disappointing year for Chris Evert Lloyd. It would also be her sixth Open victory. No one has ever looked wise underestimating her. But she has now played in four straight majors without taking a title (she won Wimbledon in 1981 but lost in July to Navratilova, 6-1, 3-6, 6-3) and admits that she lacks the confidence Navratilova now has.

Lendl's path appears more difficult than Navratilova's. John McEnroe, the No. 1 seed and still the world's No. 1-ranked player, has faltered since winning his third consecutive Open in 1981 (beating Bjorn Borg, this year's missing man). He has wononly two tournaments and has been a runner-up four times, including at Wimbledon where he lost to Jimmy Connors, who is seeded second at Flushing Meadows.

Lendl has beaten McEnroe five straight times. But anyone who saw McEnroe outlast Mats Wilander in a 6 hour 32 minute Davis Cup match in July, knows McEnroe will not give in easily, especially on his home turf.

"He's such a street fighter," said Steve Denton, who beat him in the semifinals of the ATP championships, 7-6, 6-4. "I think he's down on himself. That's his personality -- a perfectionist. He's not up to his standard of play. That doesn't mean he won't win."

In the other ATP semifinal, Lendl beat Wimbledon champion Connors for the first time (he had been 0-8 against Connors), 6-1, 6-1. "He told me later he only missed about five shots," Denton said. "To beat him like he did is a great confidence-builder.

"Ivan's playing really well," said Denton, who lost to him in the final of the ATP championships. "He's hitting well and he's got real confidence on all his shots. He's obviously someone to reckon with, more so than in any other year. He's really coming around as a tennis player. He's improved his volleys, all the little things you could exploit in the past . . . He's playing smarter, doing a few different things. He's not always creaming the ball; maybe he'll take something off. He comes in some; he's using more variety, using the whole court.

"It's going to be real close. It's going to be a really interesting Open. The No. 1 ranking depends on this tournament. It puts a lot of pressure on everyone. It makes it that much more exciting."