er winning streak stands at 25 matches now, and Martina Navrtilova claims she doesn't think about how long it might go on. "I know I'll have to lose sooner or later. But I can't think of how many in a row I can win. I could lose tomorrow, or in three months," she said, then added, "Sometimes it's better to lose and get it over with. You can get it out of your mind."

But Navratilova, who beat Bettina Bunge, 6-1, 6-2, today in her opening match in the Avon Championships, has no desire to get this tournament, the finale of the winter circuit, out of her mind. She'd prefer to leave New York with her 1982 streak--she has not lost since a December match with Tracy Austin--intact.

Although she has always been a tough competitor, Navratilova has refined and strengthened her game of late, and fairly bristles with confidence. Even her formerly severe appearance and manner have softened. She is trim, if not quite svelte, and her shoulder-length hair is a taffy color, pulled back with pastel ribbons when she's playing.

And yes, she smiles a lot more these days.

"She's got much more to smile about. Look at how she's playing," said Nancy Lieberman, the pro basketball player without a league who befriended Navratilova last summer."Martina knows now she's surrounded by people who care about her, not the ones who want things from her. She always felt she had to buy people. Now she realizes she doesn't have to."

Lieberman's friendship led to a stiffer training regimen for Navratilova, who, according to Lieberman, "used to get by giving only 50 percent effort because she's so talented. Now she works at it."

As shown by her consistently strong form throughout the winter, Navratilova's increased concentration is paying off. Her daily routine has expanded to include running for time instead of distance, and a heavy dose of basketball.

"I just love it. I'm good, but getting better at it. And the moves and skills are so similar to those in tennis, it's helped improve my game," she said. "I'd rather play basketball than tennis sometimes."

Navratilova began toughening up at the friendly insistence of Lieberman. "When I first met her, I couldn't believe she wasn't practicing enough. She didn't set specific enough goals for herself, either," said Lieberman. "So when we became friends, I said we'd train together. I asked Martina why she didn't win all the time--and I mean, all the time! Then I saw why: she was just sort of down on herself. Martina was actually a little insecure."

Navratilova, with Lieberman's help, outlined a game plan for the year. "Instead of playing in eight events and only winning five, I told her to enter five and win them all," said Lieberman. "She said, oh, I couldn't do that, and I told her, you will do that. I'm hard on her because I want her to do well."

As Navratilova played, and won, one tournament after another, her confidence soared and helped her to keep on winning. After a while, Navratilova told Lieberman, "You know, I think I can do it this way."

Besides working with taskmaster Lieberman, Navratilova enlisted the aid of Renee Richards in developing new strategies and perfecting technique.

"I need to improve my high, hard forehand volley. That's the shot that cost me the Open; if you look at Page 15 of any tennis magazine, it'll tell you that," she said. "Back five or six years ago, it was my best shot and I never thought about it. Now I'm working on correcting it so I don't swing as if I'm trying to hit the Bronx."

While pushing Navratilova through a more disciplined training program--even some football-type grass drills--Lieberman also effected the cosmetic changes in Navratilova.

"I told her to get rid of that head band and wear ribbons, instead. I also chased her around the house with a bottle of Sun-In, spraying it at her hair. Martina said she didn't want to be blond," said Lieberman. "But I told her not to worry, it'll wear off in a year."

The result of the grand-scale makeover is a more competitive, yet more relaxed Navratilova. She once fretted visibly over bad calls, but now refuses to get upset.

"I won't panic. I just don't think about it," she said. "If you do, you carry it with you too long."

She has also stopped becoming passive when she's winning. "That was one of her big weaknesses," Lieberman pointed out. "If she had somebody down 6-love, she'd feel sorry (for her opponent) and let a point or two go." Now, Navratilova plays each point hard, as if to prove her new, soft image does not cover over a tennis player gone soft, too.

Indeed, she hasn't. Navratilova likes to be in total control of the situation. At the Avon, a PR type was pestering her to set up an interview with a broadcast type.

"What about Friday, before your doubles (with Pam Shriver)?" asked the PR man.

Navratilova looked bored and annoyed. Turning to the radio man, she said, "No, not Friday. How much time you need? I'll do it tomorrow."

In her match with Bunge, an 18-year-old she has now bested five times in five meetings, Navratilova took charge immediately and methodically played through two sets that lasted barely 50 minutes.

Said Bunge, "She always dictates the pace. I didn't think I played badly, but she wouldn't let me play any better. She's just so confident. There must be somebody who can beat her. She is beatable. I think."

Navratilova's hot streak will end some day but it probably won't be here. Absent from the ranks of contenders are Chris Evert Lloyd, Tracy Austin and Andrea Jaeger. Navratilova thinks a challenge may come from Wendy Turnbull, whose 6-1, 6-3 defeat of Kathy Jordan in 79 minutes today marks her as a strong opponent for Navratilova Thursday.

"Wendy might be the best player of the bunch, and she has a style of play that can give you trouble if you're not playing well," said Navratilova. "But I'm playing well . . ."

Turnbull doesn't disagree. "She's playing very well, for sure, and all the pressure is on her to continue winning," she said. "But the other players get a bit hacked off when all they hear is that it's Martina's tournament."

"I could've played better, but I wasn't tested," she said, referring to the Bunge match. "We had no long rallies. It was a very uneventful match, but that's what I want. It's like when people ask how your flight was and you say uneventful. Then that's a great flight. I would rather have uneventful, unexciting matches. That's good."

Asked if she thought the younger players were overly intimidated by her, Navratilova shot back, "I hope so. I've earned it."

In other matches, Sylvia Hanika defeated Mima Jausovec, 6-4, 6-1, and Anne Smith upset Barbara Potter, 6-4, 7-6