John McEnroe was lucky and courageous on a day when his skills were not sharp. Bjorn Borg was superb, serving perhaps the best tennis match of his life. But, even though their routes were different, they arrived at the same place tonight: the final of the U.S. Open.

McEnroe, who habitually bemoans the fates, his luck, line calls and various demons that plague his quest for tennis perfection, came away from his struggling 5-7, 6-3, 6-2, 4-6, 6-3 victory over Vitas Gerulaitis saying: "I was lucky."

Borg, who took the court at the National Tennis Center this evening unaware of a death threat telephoned to the main switch board 90 minutes before his match started, was smiling after his 6-2, 7-5, 6-3 rout of Jimmy Connors.

"I cannot remember the last time I served that well," he said, after recording 15 aces past one of the greatest serve returners the game has ever known. "If I can just serve like that tomorrow . . . "

That's when he plays McEnroe, who ended Borg's 41-match Wimbledon winning streak in the final there, and who has been fighting himself all week. Borg, 7-6 lifetime against McEnroe seems primed for this final.

"There are no secrets when we play," Borg said. "We know what the other one will do and we just go out and play. It should be a great match."

If Borg can serve as he did tonight, he will make it very difficult for McEnroe to win a third straight U.S. Open title. Today, McEnroe escaped only because of his grit and determination and because Gerulaitis could not come up with the one big shot he needed.

In all, Gerulaitis had 15 break points in the match. He converted two. In the final set he had nine break points. He converted none.

"I was just unlucky on those points," Gerulaitis said. "I didn't play the points badly; he just guessed right every time. He had all the luck. In the fifth set when that happens, it's too good. You can't beat that."

The 3 hour 47 minute marathon, which was more brutal than brilliant, ended in a swirl of controversy. On match point, serving at 5-3, 40-15, McEnroe nailed a first serve and Gerulaitis returned it weakly.

But McEnroe, who was unusually tentative at the net all day, almost shanked the easy forehand volley. The ball landed either just in or just out. Gerulaitis saw it out. The line judge, at the the opposite end of the court, called it good.

When there was no out call, Gerulaitis turned pleadingly to umpire Leon Lipp, expecting him to overrrule the linesman. Instead, all he heard was Lipp announcing: "Game, set, match, McEnroe."

"No," Gerulaitis screamed, "the ball was out." He was immediately echoed by many in the record crowd of 18,895, an audience that had loudly supported him throughout the match.

As McEnroe, who had spent much of his afternoon exchanging words with Lipp, stood silently at the net, apparently unsure whether to celebrate or apologize, Gerulaitis continued screaming.

He finished his tirade by shouting an obscenity at Lipp that most in the stands and all in the national TV audience heard. Later, that remark cost Gerulaitis $750. His total of $5,350 in fines this year means he faces a 21-day suspension from the Men's Professional Tennis Council for going over $5,000 in one year.

Finally, realizing his case was hopeless, Gerulaitis turned and shook McEnroe's hand. Lipp, however, wasn't finished. As Gerulaitis exited, Lipp said into the microphone, voice laced with sarcasm, "Goodbye, Mr. Gerulaitis."

"I hate to see a match end like that," Gerulaitis, still angry, said later. "Usually the last point is the most important. The ball was clearly out. There was at least an inch of green between the ball and the line.

"I didn't get robbed, because he might have served an ace on the next point. But the guy (McEnroe) was getting so nervous if I'd made him play the next point I might have gotten back to deuce."

McEnroe saw the call differently, but agreed it was a bad way for the match to end. But he was glad to escape on a warm, windy day when he was often without his best weapon: the first serve. The two men split the first four sets, taking turns playing outstanding tennis.

McEnroe looked home free after winning the second and third sets with ease, losing just 10 points in nine service games. But he slipped and slightly sprained his left ankle while serving at 1-1 in the fourth set. Even though he saved break point and held the game, the momentum began to swing after that delay.

McEnroe had an uphill struggle because while Gerulaitis was serving well, the two-time defending champion was fighting himself. Gerulaitis broke in the fifth game of the fourth. He nailed a backhand down the line to get to break point and then McEnroe stunned himself and everyone else by double faulting for the break.

Gerulaitis served out the set and immediately had three break points in the first game of the final set. But McEnroe came up with an answer each time. In the third game, Gerulaitis had 15-40 and again McEnroe climbed out of the hole.

Then in the fourth game, McEnroe and Lipp engaged in a lively argument when Lipp ordered a point which McEnroe had won replayed. A fan had returned a loose ball in the middle of the point, and Gerulaitis claimed it distracted him.

"I might have done the same thing Vitas did in that situation," McEnroe said. "All I wanted was an explanation. I never got it."

Instead he got a time warning from Lipp and a broken string on his racquet, the result of his banging the racquet on the CBS mike boom directed at him during the conversation. As he returned to the court, McEnroe was booed.

He responded two ways: first by waving his hand as if by acknowledging cheers, second by winning four of the next five points for the crucial break of the match.

"The delay didn't affect me," Gerulaitis said. "I just served a bad game."

In the seventh game, Gerulaitis had four more break points. On the first three, McEnroe came up with saving shots, one a remarkable running crosscourt forehand. On the fourth, following a first serve, he tripped and almost netted a backhand volley. But it caught the net cord and the ball barely slid over.

Connors also had chances in his ninth straight loss to Borg dating back to the 1978 final here, but Borg gave him no chance to convert them. Each time Connors had Borg in trouble, the Swede rifled a serve.

Connors also fought with officialdom today, echoing earlier comments by Gerulaitis and McEnroe that the Open's corps of five line judges (as opposed to Wimbledon's 12) is defective. He screamed at umpire Jay Snyder early in the match when he failed to overrule calls that appeared wrong and called for umpire Mike Blanchard in venting more of his frustration later in the set.

But the line judges were not, as Connors himself said, his undoing. "He just outserved me," Connors said. "Almost every time I had him 0-40 or 15-40, he served his way out of it. I can't remember him serving like that against me."

Neither could Borg. "It's been a long time since I served that well," he said. "From the first game tonight, I was playing well."

Mindful of Wimbledon where he fell two sets down to Connors before coming back, Borg was all over him from the beginning. The match was full of marvelous rallies from the base line, but Borg's serve was the extra weapon he needed.

In the second set, down 1-4 and 0-40, with Connors pumped up, flailing his arms and the crowd right behind him, Borg served his way clear, with four aces in the next five points. Then he broke Connors twice in the next three serving games, each time with a backhand pass to win the set 7-5.

After that it was just a matter of time.

"Am I haunted by him?" Connors snapped when asked the question. "Why should I be. Is he a ghost?"