She is the defending Wimbledon champion. She is the defending U.S. Open champion. She is ranked No. 2 in the world. She is not satisfied.

"I said last year that I still thought my best tennis was ahead of me," Martina Navratilova said. "I wasn't so sure about it then. But now I am. I know I still haven't played my best tennis."

Navratilova, who will be the top seed tomorrow when the Virginia Slims of Washington begins play at George Mason University's Patriot Center, is 31. Because Steffi Graf, the woman who has succeeded her as No. 1 on the women's computer ranking, is just 18, people talk about Navratilova as if she is the George Burns of tennis. That, she says, rankles.

"I mean 31, come on, I'm not that old," she said. "Last year I had so many injuries it was a joke. Because my body wasn't the way I wanted it to be it affected my mind. I wasn't as confident as I should be or as I have been. Now, I feel great, mentally and physically."

It is strange to listen to Navratilova talk about 1987. People act as if she suffered some terrible fall from grace last year, largely because of Graf's emergence as a superstar in a game dominated by two women -- Navratilova and Chris Evert -- for a dozen years.

Great as she was, Graf was the loser in the two most important matches of the year, the Wimbledon and U.S. Open finals. The winner was Navratilova -- her sixth straight Wimbledon and her second straight Open. Yet, because athletes are judged on the past, people wondered what had gone wrong with Navratilova. Even though she won the two biggest tournaments of the year, she lost the French Open final to Graf after serving for the match in the third set. She lost to Gabriela Sabatini in the Italian semifinals and the Virginia Slims quarterfinals. She let a 5-0 first-set lead get away in the Eastbourne final and lost to Helena Sukova.

After that match, her frustration showed briefly when she said during the awards ceremony, "It may take an act of Congress for me to win a tournament this year." Two weeks later she won Wimbledon, proving that reports of her demise had been exaggerated. But she was not the same player who overwhelmed the sport for five years. She was very, very good. But mortal.

"Last year was a transition year for me, there's no doubt about it," Navratilova said. "I wasn't as confident about what I was doing as I've been in the past. I wasn't as sure of myself in matches as I used to be. But I think now that's different."

One of the reasons for her belief that things will be different is her new coach, Tim Gullikson. Last year, after splitting with Mike Estep, her coach for four years, Navratilova had as many coaches as the Yankees have managers. Virginia Wade came and went briefly. She approached Rod Laver and Roy Emerson, but they weren't available. Finally, she named Randy Crawford as her coach, even though Crawford was really only a hitting partner. Then, at the French Open, she brought back her former coach Renee Richards. Billy Martin might have gotten the call if Graf had won Wimbledon.

"Randy really was just a hitting partner," she said, admitting what everyone knew all of last year. "What's more, he was so quiet, he never really said anything when we practiced. If anything, he was too nice. I would say that I was tired and he would let me get away with it. Tim doesn't take any of my crap. He's got a lot of energy and a lot of things he wants to get done with my game. We've been working hard."

Gullikson retired from the men's circuit at the end of 1986 after a solid career in singles and an excellent doubles record that included a trip to the Wimbledon final with his twin brother Tom. He is the righthanded twin who helps Navratilova prepare for her top competitors. No one in the current top 10 is left-handed.

Estep, who coached Navratilova through most of her reign as the world's undisputed No. 1 player, used to say that the best thing about Navratilova was that she was coachable. Navratilova, always honest about her strengths and weaknesses, agrees. "I want to learn and I want to get better," she said. "I think Tim has been very happy with the way I've been able to pick things up. He asks me to do something and I can do it."

Yet, Navratilova's year got off to a disappointing start when she lost in the Australian Open semifinals to Evert, who at 33 remains formidable. "I was very nervous in that match," Navratilova said. "If a couple of things had happened it would have gone three sets. But it didn't. I went back afterwards and studied some tapes of five, six years ago when I was till trying to catch her. I found some things that I hadn't realized about her game. I learned some things."

That Navratilova can learn new things about Evert's game after all these years is remarkable. But it is that quality -- always finding something new and challenging in a game that has been her life for more than 20 years -- that keeps Navratilova where she is.

She has won 17 Grand Slam singles titles, but hungers for more. She wants desperately to set the all-time Wimbledon record with a ninth singles championship this summer and she wants No. 1 back. It won't be easy, though. Because the people who run women's tennis like to spread their stars out, Navratilova and Graf only are scheduled to meet in four more tournaments all year; the three remaining Grand Slams and the Virginia Slims Championships.

"I'd like to play Steffi more often than that," Navratilova said. "We only played four times last year {2-2 record, Navratilova winning the last two} and I'd like to think it will be more often this year. But I would have to change my schedule to do it and I'm really not sure I want to do that."

Navratilova has already changed her schedule this year. She is playing three straight weeks indoors now -- Washington will be the third week -- and then will take five weeks off, avoiding the hardcourt tournaments outdoors in March. Because she has a case of jumper's knee, brought on by her passion for playing basketball, she wants to stay off hardcourts until the pre-U.S. Open circuit.

She has already won a tournament in 1988 (Dallas); she says her knee feels fine and, when Pam Shriver made the mistake of saying during Dallas that she thought her doubles partner was talking a lot more confident game than she was playing, Navratilova turned around and ripped her, 6-0, 6-3, in the final. "I don't think Pam will say anything like that for a while," Navratilova said. "Most people know that ticking me off isn't a very good idea."

Navratilova was once one of the biggest women on the tour. Now, among the top 10, she is one of the smallest -- although still probably the best athlete. But one thing hasn't changed: her desire.

"I want to win every tournament I play in the rest of the year, that's my goal," she said. "I feel like I'm getting better every day. When the majors get here in the spring I'm going to be so tough you're not going to believe it."