She is competing against ghosts. She looks across the net and whom does she see? Is it Barbara Potter or Suzanne Lenglen? Wendy Turnbull or Margaret Court?

Martina Navratilova's biggest opponent is posterity. She won't say so. Think how it would sound.

Greatness is a subject that requires tact and a historical perspective, especially if you are talking about yourself. "I know it's subjective," Navratilova said. "I know there will be somebody who is 90 years old and says, 'I saw Suzanne Lenglen play and she was better.' If you're talking about titles alone, then Margaret Court was the greatest ever. If you're talking about Wimbledon titles, then maybe Suzanne Lenglen or Helen Wills Moody was the greatest ever. If you're talking about longevity, Chris (Evert Lloyd) was the greatest. But if you're talking about percentage of match victories, I'm the greatest. I've only lost two matches in two years."

She has won 108 matches and lost one, to Hana Mandlikova in January, since losing to Kathy Horvath in the French Open in June 1982. She has won the last 12 tournaments she entered, including the four Grand Slam events. On Saturday, she will play Evert in the final of the U.S. Open.

Her domination of women's tennis is such that she is now speciously compared to men. She is so good that it has become fashionable to say she is bad for the game. The irony is profound. How can a great woman athlete reflect badly on women?

The impulse to bring down Navratilova is the same one that said, "Break up the Yankees." Evert was just as dominating in her era, but, as she says, her style was less aggressive. Surely, it should be possible to appreciate Navratilova's artistry and respect her superiority. "No one says Edwin Moses is boring," said her coach, Mike Estep.

The problem is staying interested: for her and for everybody else. "My biggest opponent is staying eager," she said.

She is finding out how hard it is to be eager all the time. "After first-round matches, especially after you've won a tournament, it can get boring," she said.

Last year, the U.S. Open was an obsession. She craved it. "It seems like it takes longer to get there now," she said. "You get used to getting to the finals of the Grand Slam events. Now you just want to get it (the early rounds) out of the way so you can play that final. It's long enough when you're playing a week-long tournament. Here you get to wait two weeks."

She beat Turnbull today in desultory fashion, 6-4, 6-1. "I watched that first set," said Pam Shriver, her doubles partner. "She looked like she needed someone to kick her in the butt."

"I think she's a little different than a year or two ago," said Billie Jean King. "She's complacent but she's still winning, so it's their problem. You have to wake up every morning and remember how it feels to lose -- if she can remember that far back. It's the hardest time of life to stay No. 1."

That's where the ghosts come in. If the challenges are all from within -- then you must create specters that drive you. "That's the fun part," King said. "You can manufacture goals."

"She wants to win two Grand Slams around the corner," said Estep. "She wants to win the Open and the Australian Open and clear up the thing that says she did not win the Grand Slam."

She wants to be remembered as the best ever. "That's always in the back of my mind," she said. "It's the ultimate goal, but you can't think that five years from now they're going to say that. You have to be doing it. That's what I'm playing for. To be the best I can be and at the same time think about the long term.

"You can look past when you're working out but once you play the match, you can't be thinking ahead," She said. "I'm not putting in as much time as I did. I have to start working out more. I slacked off the last six months. But at the rate I was going, I wasn't going to be able to keep it up for five years anyway. I was going to burn myself out.

"At the beginning of the year, I was not that excited about playing already again. Even after I lost to Hana, I was moping around. Then all of a sudden, something clicked. I got it all back together. It was actually a comment by Andrea Jaeger. Someone asked if I could have as good a year. She said no, because I wasn't mentally that tough."

It takes a special kind of toughness to provide your own challenge. "But tennis is a unique game," said Don Candy, Shriver's coach. "There is always a challenge. There's a challenge to win easier, from the back court, to beat someone with a double backhand. There's a million challenges."

And there are enough of them, Estep says. "She doesn't serve like McEnroe," Estep said. "She doesn't hit ground strokes like Borg . . . A year and a half ago, she did a lot of things that needed a lot of improvement. She was No. 1 and she did a lot of things tactically wrong. She made tremendous strides and left the world. Now her improvements are going to be small. She's going to feel the pressure of everyone closing in. It's going to be hard to keep her game at that level. Her only chance of improvement is mentally, learning to play the points better."

Estep's challenge is to make practice demanding enough so that her base level of play is high enough to win, regardless of the level of competition or emotion. Usually, in practice, they play to a draw -- intentionally. "Maybe if I start beating her badly in practice (sets)," he mused. "She gets very upset. She goes berserk and breaks all the rackets. She gets too frustrated and angry if I'm winning."

After she had won her semifinal match, Evert reflected on the qualities that distinguish the champions from also-rans. "Billie Jean King once said it's not that she loves to win, it's that she hates to lose," Evert said.

Navratilova will continue to win as long as she hates to lose. Someone asked her the difference between herself a year ago and today. "Knowing I've done it and trying to do it again," she said.

She smiled at the thought.