When it was over, after she had come back from 2-4 in the final set by serving impenetrably and outsteadying as well as overpowering Chris Evert, Martina Navratilova thrust her arms straight up in the air. She turned to her friends, applauding wildly in the competitors' guest box above Centre Court, and glowed.

Even in her private reveries, she had not been able to envision herself actually doing what she had just done: crack a big first serve down the middle and drill away a deep backhand volley on the last point of the women's singles final at Wimbledon.

The 14,000 spectators who witnessed Navratilova's thrilling 2-6, 6-4, 7-5 triumph yesterday will remember her ecstatic expression at the finish, the smile that outshone the sun popping in and out from behind the mass of billowy white clouds over the All England Lawn Tennis and Croquet Club.

They will recall the flood of tears she shed into a towel immediately afterward, her puffy eyes as she received the gleaming gold champion's plate from the Duchess of Kent. The jubilant little dance step she did as she posed victoriously for the gang of photographers jostling each other behind a restraining rope.

"I thought I could win before the match, but I didn't really believe that I could be the Wimbledon champion," said the chunky 21-year-old left-hander who defected from Czechoslovakia to the United States in September 1975 and now lives in Dallas.

"It's only once a year that you get the chance, and this was the first time that I was in the finals. Most people thought that Chris would win, but I came through." The most important believer had believed.

"I always wondered what it would be like. If I could sleep the night before? How it would feel going on the court? If I could keep walking if I had to serve for the match? What I would do if I ever won? It's very different from what you think . . .

"I don't know if I should cry or scream or laugh. I feel very happy that I won, and at the same time I'm very sad that I can't share this with my family."

Navratilova has not seen her father Miroslav, an "economic engineer" in the office of a Prague factory and her first tennis coach, her mother or 15-year-old sister Jana in nearly three years.

She talks to them frequently by telephone, but she has been unable to visit them since being granted political asylum in America during the 1975 U.S. Open tennis championships.

Their applications for tourist visas to the United States and England have been rejected. Martina's attempts to secure them a permanent visa so they can settle in the United States also have failed.

Her victory might help in these efforts, and in that sense it was far more precious than the $32,000 first prize and the incalculable professional self-esteem that comes with winning the oldest and most cherished title in tennis.

She is the second expatriate Czech to win Wimbledon. Jaroslav Drobny captured the men's singles title in 1954, while traveling on an Egyptian passport.

"I like the United States very much. The people there have been very good to me. But deep down I will always be a Czech, just as Drobny was always a Czech," she said.

Navratilova had a right to be proud as well as joyous. After losing four straight games from 2-0 to 2-4 in the third set, she did not unravel.

On her own serve, she played brutally agressive tennis. On Evert's, she was firm and patient in deep, fiercely contested baseline rallies, awaiting her opportunies to smack an approach shot and press the attack from the net.

She played with unshakable resolve when everyone expected her to get nervous. She looked Evert, the champion of 1974 and 1976, straignt in the eye, and it was the legendary Ice Maiden who cracked.

Navratilova, whose emotions once overwhelmed her abundant talent, won 12 of the last 13 points. She held at love the last two times she served, missing only one first serve.

It was Evert, who made three unforced errors in the end, losing to her serve to 5-6 in the most crucial moment of the absorbing 1-hour 43-minutes match.

"I was just a notch better at the closing stages, which is the only thing that matters. I was able to raise the level of the game, and Chris kind of stayed the same or even got worse," Navratilova noted correctly.

Evert agreed. The championship had hinged on a wholly unexpected psychological role reversal.

"She's just tougher than I am right now," Evert said. "In the past, the shoe has usually been on the other foot. I've been the consistent one. But she's really matured - on the tennis court and off - and it showed up," said Evert, 23.

"She used to be very emotional and moody. Now she seems relaxed. She's been through a lot in the last couple of years - a lot of bad feelings, hurt and loneliness as far as her defection is concerned. Now she seems to have it all together.

"A couple of times I heard her talking to herself, but she didn't get flustered at all," Evert continued. "At 2-4 she could have gotten discouraged. Two years ago, I think she would have. She might have given up a little bit, made a lot of erros, gone for impossible shots. But she played consistenly and forced me into the errors."

The tennis was patchy, especially in the first two sets, largely because of a swirling wind that rustled the green canopy over the royal box.

Both players had some difficulty finding the range on groundstrokes in the first set. Navratilova even suffered the embarrassment of whiffing completely on an easy overhead.

She took her eye off the ball, and a gust caught it. She swung and missed, whirled and desperately tried to get to the ball after it bounced, but couldn't. Then she stood with head in hands for a few moments, stunned.

Evert - who lost her serve at 15 in the first game of each set - buzzed a backhand cross passing shot on the next point to break back to 1-1. But the enormous error actually may have helped Navratilova. "It kind of woke me up. After that I paid more attention to the ball," she said.

By her own admission, Navratilova played "in a bit of a daze" in the first set. She did not move well. She held her serve only once. When she was broken from 40-0 for the set, in a game in which Evert got two lucky net court winners, depression seemed to be setting in.

She sulked and sent a couple of persecuted, hangdog glances toward the guest box where Sandra Haynie, the friend who shares a house with her in Dallas and manages her business affairs, was seated.

But after losing her serve in the game of the ignominious whiff, Navratilova settled down and played much more positively. The looks toward Haynie, who has been an important stabilizing influence in her life, were more optimistic.

Navratilova played an attacking game to break for 2-1 crunching a backhand volley that Evert couldn't handle. After blistering a short second serve at 15-40, she held her serve at love with a spinning drop volley and raised her arms triumphantly, as if to say, "I finally held an advantage."

She fell behind, 15-40, in her next service game when Evert, having followed in a near-perfect drop shot, drilled a forehand volley that hit her in the ear. Navratilova took two steps and dropped to her knees, rolling her eyes and feigning death by shooting.

Evert, at first concerned, smiled, reached across the net and patted her opponent playfully on the head. It was that kind of a sporting and good-natured match between good friends. Navratilova later insisted that a point on which Evert got a bad call be replayed, but when the laughter died down after the "killer" volley, Navratilova put in six straight first serves to dig herself out of trouble, holding for 4-2.

An athletic 5-foot-8 and 145 pounds, Navratilova has the oppressive weight of shot in women's tennis today. Her powerful serves and telling volleys were there when she needed them. She put in only 14 of 31 first serves in the first set, 27 of 42 in the second, 22 of 35 in the third, including seven of the last eight.

After trailing 0-2, in the final set, Evert temporarily picked up the pace and accuracy of her groundstrokes. She played her best game to break for a 4-2 lead, blasting two return winners off first serves to get to 0-40, then lacing a backhand cross-court for an outright winner off a fierce, scrambling rally.

But Navratilova broke right back to 3-4, even though Evert put in five of five first serves. Navratilova remembered their only previous meeting this year, when she recovered from 1-4 in the final set and saved a match point in beating Evert, 9-7, in the third.

Evert held for 5-4 after saving a break point at 30-40 on another magnificient all-court point. Navratilova hit a smash down the middle, Evert drilled the ball right back at her with a forehand and Navratilova slashed a low, forehand cross-court volley that looked like a sure winner. Evert got to the ball and, on the dead run, cranked an impossible backhand cross-court passing shot that bit into the turf, a foot inside the sideline.

That, however, was Evert's last hurrah.

Navratilova, damning the torpedoes and boring full speed ahead as she served to save the match, held at love.

She played steadily in the next game as Evert made those three unforced errors to lose her serve, sailing a forehand on the last point.