Bjorn Borg, so good a tennis player that he seems to have no anxieties whatsoever on the court, is due to be married next month to Mariana Simionescu, the Romanian player who has been his fiance and globetrotting companion since 1976. Borg says that he is bound to feel some of the nervous quivers customary for bridegrooms-to-be the week before the July 24 ceremony in Bucharest.

Well, maybe. Borg is not the nervous type.

Certainly he is not jittery now, about tennis or his upcoming nuptials. He appears supremely fit, relaxed and confident on the eve of the Wimbledon championships, which begin Monday at the All England Lawn Tennis and Croquet Club.

Borg has been made a 4-to-5 favorite by London bookmakers to win the men's title -- the "gentlemen's singles," as it is known in Wimbledon's precise and proper parlance -- for a fifth consecutive year, a feat no man has accomplished since tennis was a polite diversion for Victorian ladies and gentlemen.

Two weeks after winning the French Open for an unprecedented third straight year and fifth time overall on slow Parisian clay, Borg is aiming for a royal flush last achieved on fast Wimbledon grass by Englishman Lawrie Doherty in 1902-06. Historians will note that Doherty won the first of his five successive titles the year after Queen Victoria died.

"I know that Mariana is thinking more about the marriage than I am for the moment," Borg allowed during a rambling conversation recently. "To me, it doesn't seem like such a big deal. We've been together four years, so nothing is going to change."

A typically stolid Swedish view of what is being regarded as one of the highlights of the European social season, complete with three ceremonies: the Greek Orthodox church wedding for 200 family and close friends in Bucharest, followed closely by elaborate reenactments for business acquaintances and more casual friends in Monte Carlo (Borg's official residence where he has a house and tax shelters) and Marbella, Spain (where he maintains an apartment).

The triple-wedding spectacular is being organized by Regine, the Paris-based proprietress of jet set night clubs, who has Borg under contract for rather nebulous services that fall under the category of impressing her fast-living and quick-spending clientele.

Photo and film rights to the wedding have been sold by International Management Group, Mark McCormack's Cleveland-based firm that handles Borg's business affairs, supplementing his $500,000 or so in prize money winnings with annual endorsement, exhibition and appearance income in excess of $3 million.

"I am not going to worry about the wedding much until after Wimbledon," said Borg, just turned 24, who is by nature a man of simple T-shirt and jean tastes. A decent, pleasant but scrupulously guarded, almost universally liked and respected fellow, he is unextraordinary except on a tennis court, where he is an incomparable master.

Borg is happily and thoroughly devoted to Simionescu -- a bouncy, good-natured young woman who willingly sacrificed her own modest tennis career for his, and exudes her infatuation for him becomingly.

For the next two weeks, however, he is preoccupied with another manner of love. It is no coincidence that Borg's disappointing, ghost-written autobiography -- which is being excerpted in one of London's tabloids this week -- is subtitled "My Life and Game," for tennis comes first in everything he does, at least for now.

After winning the world's premier tournament for the fourth straight time last year, Borg gave a rare glimpse of his true ambition when he said: "One of my goals in the future is to win maybe a lot of big titles and to make some records if I can, so maybe one day they will say, 'You have been the greatest player of all time.'"

He is more mindful of historical milestones, more determined to better them than he generally lets on. Scandinavian reserve and his natural modesty -- attractive traits in these days of enormously inflated egos, surly tempers and inexcusable bad acting in tennis -- make him seem a particularly unflamboyant member of a brash fraternity.

But Borg's intensity on the court, his machinelike efficiency and impassiveness, and the consistently high level of his performance all give him a distinct and strangely appealing personality. Ilie Nastase calls him The Martian, because "He is like a robot who never makes a mistake . . . he must be from outer space."

Though undemonstrative compared to arch rivals Jimmy Connors and John McEnroe, who are in the other half of the 128-man draw and seeded to meet each other in the semifinals, Borg is as highly motivated as any player alive. "I hate to lose, I have always hated to lose at anything," he says -- especially when a record is within grasp.

Borg has won 28 matches in a row at Wimbledon since Arthur Ashe beat him in the quarterfinals in 1975, and has his heart set on eclipsing the all-time record of 31 straight held by Australian Rod Laver. (Laver won the sport's most cherished title in 1961-62, then turned professional and was not eligible again for five years, when "open competition" was approved and the pros were welcomed back into the game's mainstream. He reclaimed the Wimbledon title in 1968-69 and won three matches in 1970 before Englishman Roger Taylor ended the streak at 31.)

Borg's international goal is to win four rounds and supplant Laver in the record book. This seems almost inevitable, given the draw that has kindly steered him clear of most of the big servers who can be so troublesome to favorites during Wimbledon's first week. Then he will go after Doherty, whose five titles came in the pre-1922 era of the "challenge round," when the defending champion sat out until the final, waiting for a challenger to claw through the draw. (Doherty's five titles encompassed only a 10-match winning streak).

Thus, all things considered, Borg's wedding plans likely will have to do without his personal attention until July 5, when the men's title will be decided in the stately, Elizabethan-style Centre Court arena -- the grassy stage that Borg, like most champions of the past and present, holds most dear.

"There will be time after Wimbledon," he said. "The week before the wedding, then I will be nervous, for sure."

Borg nervous? Most of his colleagues would like to see that. The majority never has seen him flinch on the court, except briefly toward the end of last year's memorable, five-set Wimbledon final against Roscoe Tanner. For a few games in the tingling final set, Borg acknowledged afterward, he was so scared he could hardly hold his racket. He came through in the crunch, though, and won, 6-7, 6-1, 3-6, 6-3, 6-4.

Of the many Borg qualities that his fellow pros admire -- his superb speed, strength, stamina, concentration, competitiveness and consistency -- the one held in the highest esteem is his match temperament. "Ice in the stomach," the Swedes call it.

He never seems to get ruffled or rattled and, in the manner of grand champions, is able to produce his most sublime shots under pressure. At moments when most players are paralyzed by anxiety, he seems to have no nerves at all.

Lennart Bergelin -- who became Borg's full-time personal coach, adviser, confidant and masseur after captaining the Swedish Davis Cup team from 1970-75 -- recognized this exceptional quality early, even before Borg came back from two sets down to beat experienced New Zealander Onny Parun in a Davis Cup match when he was only 15.

"He has the right kind of courage," the taciturn but shrewd Bergelin elaborated in 1974, when Borg lost the first two sets and then crushed Spaniard Manuel Orantes in three straight to win the first of his French Open titles at age 17. "This is a gift, it cannot be learned."

Other players marvel at the gift, less in envy than in appreciative awe.

"Borg is a genious, there is no question about it," says Vijay Amritraj, the elegant Indian who has come closest to beating the Swede at Wimbledon during his winning streak, three times forcing him to serve at match game down in the second round last year. "He has an uncanny ability to raise his game on the most important points. He is most dangerous when in danger. For a long time I thought Laver was the best player I would ever see, but I think Borg has surpassed him already, and he is still improving.

This tendency to soar when others crash comes as naturally to Borg as the stubble that sprouts on his chin just before and during major championships, when he superstitiously puts away his razor.

"I think probably I was born with that," he says when asked about this ice in the stomach. "I remember when I started to play the circuit, I was more nervous because I was not used to playing big matches. But not for the last five years. I have been playing so many big matches, when maybe one ball makes the difference, that I got used to that.

"It's very difficult to tell a player that he has to be more relaxed, because the way he is is the way he is. If he is tight or nervous at 30-40 on his serve, there's no way he can change that, because that's his personality.

"I feel more relaxed when it's 30-40, or a crucial point in the match. I'm not tight or anything when I'm tossing up the ball and making my swing. Maybe that's why I get my first serve in most of the time at 30-40.

"I know a lot of players might get tight because they're thinking, 'I'm break point down, I have to get my first serve in or I'm in trouble.' Their arm gets heavy, they have trouble to make a good toss. But I am thinking that for sure I will get my first serve in, so I'm very relaxed."

He was reminded that after his narrow escape against Amritraj last year, he said he is more relaxed when he is behind. "That's true. When I'm behind, I always think that I'm going to lose, so I decide to go for my shots, to try to make shots I didn't make before," Borg said.

"I always try to play a safe game, to make the other guy take the risk, but when I'm behind I take more chances. I gamble more, go for winners, and because I'm so relaxed I usually win those points."

Borg knows that he must lose sometime, though. He is prepared for that, and takes defeat as graciously as he does victory, even though he has little practice at it.

"I accept it more easy now than maybe five or six years ago," he said. "There is no way you can keep going, winning every time. That's impossible. No one has ever done that. I hate to lose even more than I like to win, so I get very depressed right after the match when I lose. But then two or three hours later, it's over. I always look ahead and think, 'Okay, I might play the same guy next week.'

"As long as I have been trying my best, trying to win, trying to reach every single point, then it is all right. If I do that and still lose, I realize: 'Okay, the other guy was better than me today, so what can I do? I tried everything. That's it." A faint smile and even a little twinkle appears in his close-set pale, glacial eyes. "I never go to my room and scream or break the furniture, nothing like that."

Borg says he feels the pressure of his mounting Wimbledon streak, even though it doesn't make him nervous.

"I know I can't win forever, and the other guys are usually playing well against me because they have nothing to lose. I'm the one who has all the pressure on me," he said. "No one will say anything if they lose in three straight sets, but if they win it is a big thing. It was the same for me when I was coming up. When I was playing the top players, I felt I had nothing to lose, everything to gain."

Other players take a different view, however.

"When somebody finally beats Borg at Wimbledon, it's automatically going to be one of the biggest single-match wins of the century" reasons Californian Erik van Dillen.

"That works in Borg's favor, because when a guy gets close -- the way Amritraj did last year, and Victor Amaya the year before -- the pressure on him is incredible.Borg is used to it, the commotion and the tension and the hundreds of photographers who come running when they smell an upset. He's protecting the streak, but there's more pressure on the other guy, who knows this might be his one chance to make history."

Borg unquestionably is a physiological phenomenon. He has a regular pulse rate of only 35, and blood pressure of 70 over 30. Dr. Carter Rowe, an eminent Boston surgeon, recently wrote about him in the venerable New England Journal of Medicine, concluding that he is an almost perfect athlete who used nearly every muscle in his body, harmoniously, on nearly every shot.

But happily, Borg has enlarged on the great physical gifts with which he was born with diligence, hard work and a sensible life style encouraged and overseen by Bergelin, his friend, father figure, and magic-fingered masseur.

No one practices longer or more purposefully than Borg, whose workouts are devoid of nonsense but not of joy. He loves hitting a tennis ball, competing and knowing that he is the best in the world at his chosen craft.

"It feels great," he says. "There is no other feeling like that, knowing that you have been working so hard, making sacrifices, and they are worth it."

Vitas Gerulaitis, Borg's favorite practice partner, continues to work out with him before big tournaments even though he is 0-for-19 in their head-to-head rivalry. He knows Borg whips him into shape that makes him capable of beating anyone else, and he admires Borg's voracious appetite for work.

"He deserves his $1 million racket contract and $3 million a year and everything else he has, because since he was 12 years old he's worked harder than anybody else," says Broadway Vitas. "The guy was out there practicing eight hours a day. I don't begrudge him a thing. I think he's earned it all."

Borg plays essentially the same game, based on hitting exaggerated top spin ground strokes off both forehead and backhand, against all types of opponents. It is a game bred on slow, European clay courts, but he has been able to adapt it to fast surfaces because he has exceptionally quick hands and feet.

"Most of us thought it was a kind of fluke the first time lhe won Wimbledon in 1976," says Ashe, the last man to beat him there. "Hell, nobody in 30 years had been able to win on grass from the baseline hitting top spin the way he does.

"But his serve made a quantum leap -- at least a 50 to 75 percent improvement -- and his return of serve is tailor-made for grass, because he stands about two or three yards behind the baseline and just lets the top spin take its natural course.

"His hands are quick enough that he can change grips and handle the fast, skiddy bounces on grass, which is unusual for a European, and his shots just come over the net and dip. Anybody who tries to come in and volley against him is hitting up all the time. It's tough to put the ball away that way, and he runs everything down and is in a position to hit a passing shot.

"He also moves incredibly well on every surface. It's tough to move fast from side to side on grass, because there isn't much adhesion between the sole of the shoe and the court, but he can do it. He's gotten better and better."

Borg once doubted, as did most tennis isiders, that he would ever win a big tournament on grass, a fast surface given to low and capricious bounces. He had a clay court game, but he was able to adjust that. The fact is that grass court tennis accentuates athleticism, and Borg may be the best athlete in the game.

"Maybe five or six years ago, I was not that comfortable to play on really fast surfaces. I knew I could play well once in a while, but I would have to improve my game a lot if I wanted to win Wimbledon," said Borg.

"I knew especially I had to improve my serve, so in 1976 I was working a lot on that -- the whole year, but mostly the two weeks right before Wimbledon. I was practicing the serve an hour every day, which I had never done before, and Lennart made a change that was very important. He told me that my position was not exactly right.

"He changed my left foot to be a little more straight, pointing to the net. I had it on the side, like this," he went on, jumping up and demonstrating how Bergelin shifted his front foot from almost parallel to almost perpendicular to the baseline.

"Now when I serve, I have my body pointing to the net, and I toss up the ball right in front of me. The other way, I was tossing the ball more to the right side, and I didn't know exactly where it was going. I was mishitting too many serves. This way, I always have a good toss, and I hit through the ball, with my body moving forward toward the net, so I get more power."

Bergelin, who was a Wimbledon quarterfinalist himself, also convinced Borg that he had to be more aggressive.

"I had to work on developing that kind of game -- not serve-and-volley all the time, because that is not me, but just to come in to the net more, so that the opponent never knows exactly what I'm going to do," says Borg. "I worked on that luntil I was comfortable playing that kind of a game, too, and by coming in more I improved my volley a lot. I still can improve it more, but right now I am very satisfied."

Borg now has an impressive all-court game -- the best ground strokes in the business, one of the best serves, and a serviceable volley that is more than adequate because he usually gets to the net behind thumping approach shots that have the opponent out of position.

Some players consider Borg's game to be futuristic tennis -- a defensive style so highly developed that he can use it to attack. His timing, which is the key to hitting his top spin with such intimidating pace, is extraordinary. The ball even sounds menacing as it fizzes off his racket with a high-pitched, space age "ping."

Borg's rackets are strung at an unbelievably tight 80 pounds of tension. He has been known to break as many as 60 in one tournament, and always travels with a formidable arsenal of equipment since restringing is almost invariably left to Mats Laftman, who lives in Stockholm and supplies Borg with rackets all over the world.

The savvy Bergelin, a prototypal cornerman and aide-de-camp, is in charge of the equipment, as well as travel, hotel, meal and practice arrangements. He is, in effect, Borg's road manager and shield from an intruding world. At tournaments, he screens all phone calls and sees that Borg has no concerns except showing up for his matches fit and ready.

As a teen-ager, Borg tended to let himself be overscheduled, much as John McEnroe is now. Bergelin talked him into a saner aproach, and is always at hand to encourage the proper discipline. Borg is well-regimented, so they make an outstanding pair, and the result is that Borg almost always comes into a big tournament in peak form, mentally and physically. He is expertly prepared as a thoroughbred in the care of an expert trainer.

This year, Borg has pared down his scheduled even more than in the past. He still plays many high-priced exhibitions -- in eight days this March, for instance, he played in Mexico, Paraguay, Chile, Denmark and Germany -- but he lumps them together and then takes sensible rest periods before tournaments.

"I made up my schedule last December and have followed it exactly. So far it's working out well," says Borg, who has won 40 of 41 tournament and Davis Cup matches he has played in 1980, coming into Wimbledon.

"I never play more than two tournaments in a row now, so I come into every match feeling 100 percent eager. That's when I play my best tennis."

When he gets away from the tour, he forgets about tennis completely and recharges his batteries.

"I just like to be with Mariana and our friends, to have a good time and not speak about tennis," he says. "I like to play a little bit of soccer, or table tennis, or go out to the movies or a restaurant or a discotheque. I like to go to the beach, or water-skiing -- anything to get away from the tennis, to be with friends and have a beer and speak about other things."

Top matches Monday: Center Court

Bjorn Borg, Sweden, (1) vs. Ismail El Shafei, Egypt; John Feaver, Britain vs. Ilie Nastase, Romania: Vijay Amritraj, India, vs. Jose Luis Clerc, Argentina (16). No. 1 Court

John McEnroe, U.S., (2) vs. Butch Walts, U.S. Vitas Gerulaitis, U.S., (4) vs. Stefan Simonsson, Sweden. No. 2 Court

John Sadri, U.S., vs. Billy Martin, U.S.; Jimmy Connors, U.S., (3) vs. Richard Lewis Britain; Victor Pecci, Paraguay, (8) vs. Matt Mitchell, U.S.