-Bjorn Borg, who at age 23 already must be considered one of the greatest tennis players of all time, won his fourth consecutive Wimbledon singles title today in perhaps the most excruciating match he has ever played.

The astonishing Swede, who was made an almost prohibitive 1-to-7 favorite by London bookmakers after routing arch rival Jimmy Connors in the semi-finals, was stretched to the limit of his ability and will be the agressive serving and volleying of left-hander Roscoe Tanner before winning, 6-7, 6-1, 3-6, 6-3, 6-4.

Tanner, in the final of the world's oldest and most revered tennis tournament for the first time, was at Borg's throat for the duration of the splendid 2 hour 49 minute match, gambling on first serves, going to the net consistently on Borg's as well as his own second serves, attacking at every opportunity.

When he saved three match points as the champion served from 5-4, 40-0 in the tingling fifth set, even Borg- the seemingly unshakable marvel who has a pulse rate of only 35 and the quality Swedes call "is I Mage" (ice in the stomach) / admitted that he had "never been so nervous in my life."

So it seemed with 15,000 sweaty-palmed spectators around Centre Court of the All England Lawn Tennis and Croquet Club as Tanner drilled a back-hand down-the-line approach winner, nailed a short second serve with a backhand return and got to the net for a savage forehand volley, then sliced a backhand approach shot that Borg jumped at and netted with a forehand volley on those first three match points.

"That was unbelievable. When I had 40-0, I almost couldn't hold my racket, I was so nervous," said Borg, who desperately wanted to become the first man since New Zealander Tony Wilding in 1910-13 to win here four successive years.

"Then, when it got to deuce, I was thinking that if he won that game to 5-all, then there is no way I would win the match."

Tanner, who went into the match thinking "there was no reason to feel nervous, there was no pressure on me," and played with an aggression that was just on the right side of reckless, danced up (See WIMBLEDON, 7, Col. 1) (WIMBLEDON, From D1) and down and swayed hungrily as he waited to receive Borg's next serve.

The Swede, uncharacteristically tight after taking a 2-0 lead in the final set, had ceased going for his "toonder" first serves and was spinning in safe deliveries at three-quarters pace, not wanting to miss and give Tanner a crack at his second serve.

He did so again at 5-4, 40-40, but Tanner went for a big backhand cross-court return and hammered the ball into the net to fall match point down for the fourth time.

This time, the plucky native of Lookout Mountain, Tenn., was unable to hit a forcing return off Borg's first serve. The ball came back deep and kicked high off the chopped-up turf near the baseline, and Tanner raked a hurried backhand well wide down the line.

As Tanner's shot sailed out, Borg dropped to his knees in the back court, raised his arms and looked up ecstatically at the competitors' guest box where his parents sat with his fiancee, Romanian player Mariana Simionescu, and his coach, Lennart Bergelin.

Borg got up quickly, but raised his arms twice more - once on his way to the net to shake hands, again as he went to the sideline to await the trophy-giving. He looked not only satisfied but vastly relieved to have survived what he called "the toughest match I have played here, absolutely."

Borg has won 28 consecutive singles matches at Wimbledon since Arthur Ashe beat him in the 1975 quarter-finals, but he felt this one was more difficult than his five-set early-round scares against Victor Amaya (1978) and Vijay Amritraj (second round this year), the 1977 smeifinal in which he beat Vitas Gerulaitis, 8-6, in the fifth set, and the final that year in which he beat Jimmy Connors, 6-4, in the fifth.

"I always felt that I was one step behind Roscoe, even when I was a break ahead of him in the fifth set," said Borg. "I always was a little bit behind because he was serving so well. I had so many problems to break his serve."

Borg, in the fifth set, was like a gallant champion who knows he is ahead on points in a title fight and is struggling with all his heart to get through the 15th round without being knocked out by a challenger throwing Sunday punches.

After more than 21/2 hours of slugging, with Borg's incomparable ground strokes and will pitted against Tanner's determination to bore in on the net, both men agreed that this match came down to one game: Borg serving at 4-3, 15-40 in the last set.

A long forehand off a forcing return of a second serve and a forehand volley error got Borg into a hole at 0-30. And when Borg couldn't make a forehand scoop, running in to cover a sharply angled volley, to make it 15-40, someone in the gallery said: "This is where champions show up to play."

"If I win one of those next two points for 4-all, I'm going to feel exhilarated and he's going to feel a little down, and that changes everything around," Tanner said later.

He had his chance, a wide-open forehead passing shot down the line with Borg moving in the wrong direction. But Tanner steered the ball into the doubles alley and dropped to his knees, head down.

"I had a great chance on that one, but I held my stroke just a fraction of a second, trying to get him to lean the wrong way, and played it a little too fine to the line," Tanner said. "I should have just hit it, because he was looking for the cross-court all the way, but you don't know that until after you make the shot."

At 30-40, the 1973 Stanford graduate chipped a backhand approach shot off a rally and went in but netted a low backhand volley - one of his most reliable weapons - almost from his knees.

"He hit it right where I wanted it, since the backhand volley is my favorite one, but he put a lot of top-spin on the ball and it dipped as it came over the net. I kind of lost sight of the ball as it dropped," Tanner said.

Back to what an old-time tennis player once deemed "the blessed sanctuary of deuce," Borg got the advantage with a first serve wide to the backhand that Tanner returned inches long.

Tanner hung his head momentarily, thinking the ball had been good, but on the next point picked himself up and worked in to the net again. Borg cranked a sharply-angled forehand cross-court pass - a lovely heartbreaker of a shor - to get to 5-3.

The crowd, which included such divers notables as actor Charlton Heston, former world champion racer Jackie Stewart and King Constantine of Greece, plus the three lads from Surrey who had waited in line for a week for tickets and wore top hat and tails to the match, was panting now.

The imposing, Elizabethan-style Centre Court, often so hushed that it seemed like a cathedral, echoed with squeals, cheers of encouragement and thunderous applause for both players.

This final was not expected to build to such a fevered pitch. Borg - whose long, unkempt blonde hair and scraggly beard makes him look ever more like a holy man - had produced such miraculous tennis against Connors in the semifinals that few people gave Tanner a chance.

But the improving left-hander - who now complements his always impressive serve with more consistent ground strokes, quicker and more agile footwork and assured volleying - came into the match in an attacking mood.

"You've got to take chances against Bjorn. You can't go out and just play careful tennis because he's better than anybody else at that type of game," Tanner said. "You've got to take some chances on his second serve, mix up your serves and keep him from getting into a groove.

"If you play just a steady, hardhitting game, he likes that. You've got to do some things to break up his rhythm, take some gambles, go for your shots all the time. You can't worry if you miss some, because if you start staying back and playing his game, you're going to get beaten for sure."

Borg already canonized in the British press, started a bit hesitantly, uncomfortable in the chill breeze that swirled the dust on Centre Court on an overcast day.

"It was very difficult even to get the feel of the ball, to have the rhythm on the ground strokes, because you don't know what the wind was going to do with the ball - especially on the job," said Borg, who, therefore, had little confidence in the shot he ordinarily would have used to keep Tanner from crowding the net.

Tanner demonstrated early that he would win many points on his serve, especially wide serves to Borg's two-fisted backhand that either went for outright winners or jerked the Swede so far out of court that they opened it up for easy volleys.

Tanner served oppressively to the advantage court in the first and third sets, and even though he only got 91 of 167 first serves in, they were effective because of their variety of pace and spin, their placement and the strong second serves with which he backed them up.

"I missed a lot of first serves, but overall I felt I served a good match," he said. "I was going for it, very close to the lines, and I mixed it up pretty well because I didn't want him to get the rhythm of returning any particular serve."

Tanner lsot his serve only four times in five sets.

There were no service breaks - in fact, only 24 points against serve - in the first set, which Tanner won in a tie breaker, 7 points to 4, as Borg dropped the last two points on his serve.

Flushed with success, Tanner hurried a bit and started serving shorter in the second set. Borg finally loosened up and began crackling his returns and passing shots off both wings.

But in the third set, Tanner escaped three break points in the first game with winning serves, got to advantage with one of his 74 aces, held and then broke Borg in the second game. Tanner saved three more break points in the seventh game and served out the set as the crowd buzzed with anticipation of a spectacular upset.

But Borg says he is proudest of his ability to come from behind, and he showed he could do it again today. He broke Tanner with a screaming forehead return down the line for 3-1 in the fourth set, served out the set and broke again in the first game of the fifth.

"I think there was extra pressure on me because Roscoe was serving well," said Borg. "I knew I had to hold my serve every time, or I might not break him again."

He also had three break points for a 3-0 lead in the final set.

"It was very important that I get a break right away in the fifty, but then I was getting a little bit tight, I wasn't moving my legs. That was just nerves, but I was scared to come in to the net."

Until, that is, Tanner had saved those three match points at 5-4.

"Then I told myself, I just have to take a chance, and go in," said Borg, who was following his first serve to the net when Tanner missed the return that put him at the last match point.

In the end, Borg took a leaf from Tanner's book and won like a champion, going for his shots, taking a calculated gamble. CAPTION: Pictures 1, 2, 3 and 4, Four years a Wimbledon champion: Bjorn Borg with Duke and Duchess of Kent, above, 1976; accepting applause, bottom, 1977; giving thanks, right, 1978, and holding this year's trophy, far right. AP and UPI; Picture 5, Bjorn Borg plants kiss on trophy after defeating Roscoe Tanner for fourth straight Wimbledon title. UPI