Francisco (Pancho) Segura, the swarthy Ecuadorian who gives tennis lessons to champions, celebrities, and anyone else who can afford to pay his high-rent-district fees, was sitting on Court No. 1 at the All England Lawn Tennis and Croquet Club Tuesday afternoon, watching Jimmy Connors struggle into the semifinals of the Wimbledon Tennis Championships.

Can it really be five years since Segura, then Connors' favored tactician and corner man, ambled jauntily on his bowed legs into a packed interview room and crowned his man the once and future king of tennis' most cherished tournament?

Flushed with the deciseveness of Connors' 6-1, 6-1, 6-4 victory over an Australian legned named Ken Rosewall in the 1974 final, Segura grinned through his prominent teeth and declared:

"Jeemy is ruthless, he is a keeler. He has the heart of a lion. He will dominate the game. He will not win Wimbledon one time, he will win 10 times."

Since that day, Connors has won three U.S. Open titles -- the first the same year, over Rosewall again, and even more lopsidedly -- but never a second at Wimbledon. He has been the runner-up three of the past four years, but Bjorn Borg has been a more ruthless killer, more lion-hearted, the man who has come to dominate the game.

In 1974, Connors seemed to have a stranglehold on the game of tennis. He lost only four matches that year, and swept the Australian, Wimbbledon, and U.S. open titles.

The lyrics of a song popular at the time, sung by the late Jim Croce, seemed made to order for the world's best and baddest tennis player: ". . . You don't pull on Superman's cape you don't spit into the wind, you don't pull the mask off an old Lone Rager, and you don't mess around with Jim."

But somehow, ever since Arthur Ashe dethroned him in the 1975 Wimbledon final, exposing for the first time his vulnerability to junk balls hit short to his forehand, Connors has never been the force he was when Segura bequeathed him the 1970s in advance.

Instead it has been Borg, whose icy impassiveness provided such a contrast to archrival Connors fiery temperament, who has come closer to fulfilling Segura's prophecy.

The stolid Swede lost seven of his first eight meetins with Connors, between 1973 and 1976, but has won seven of 10 since, including the last two Wimbledon finals. He has won three consecutive singles titles hre, a feat last achieved by Englishman Fred Perry in 1934-36. Borg is going for fourth title here, which no man has accomplished since New Zealander Tony Wilding in 1910-14.

While third-time semifinalist Roscoe Tanner and first-time anything Pat DuPre, who meet Thursday in one semifinal, harbor their own fond dreams of holding aloft the championship cup come trophy-giving time at Centre Court Saturday, virtually everyone expects this year's champion to be decided in the other semifinal matching Borg and Connors.

On current form and recent past performance, most knowledgeable observers are picking Borg. He beat Connors in the 1977 final, 3-6, 6-2, 5-7, 6-4, 6-2, 6-3. And he has beaten Connors in their only two meetings this year, 6-2, 6-3, at Boca Raton, Fla., and 6-3, 6-2, at Las Vegas.

"I don't see how Borg can lose, on the form that's been shown to date," says Lew Hoad, the still-imposing Australian who won Wimbledon in 1956-57, and is part of the three-man International Tennis Federation panel that designated Borg the 1978 world champion.

"He's been much more impressive his last few matches. Personally, I don't think that Connors has played enough tennis to get into form." Connors played only one tournament -- the French Open -- from the first week in May until Wimbledon, and only decided at the 11th hour to come here instead of staying with his wife in Los Angeles as she awaits the birth of their first child.

"Tennis is a game that, to a certain extent, you have to play all the time, so that you get to do things automatically," Hoad said.

"Jimmy's not returning serve nearly as well as he used to. He's not reaching as quickly to his opponent's shots. That's what happens when you don't play enough and your instincts desert you."

Fred Perry, another member of the ITF panel, agrees. "I've said Borg would win it all along, and I've seen nothing to make me change my mind," he said.

Connors is just not as sharp as he was. He's not as quick around the court, and this seems to affect the speed of his shots. He doesn't get into position to hit the ball as well as he once did, and his serve is not as penetrating. He doesn't get rolling with streaks of eight and 10 games anymore.

"I don't know why Conners doesn't use the swerving serve that he used to have, that tailed away from right-handers. He doesn't use his serve as a weapon anymore," said Perry. "His second ball sits up and begs to be hit. Jimmy's serve was just awful against [Bill] Scanlon in the quarterfinals. He just doesn't use that swerving serve he used so effectively against Rosewall."

Why? No one knows for sure.But as Segura will attest, it is not 1974 anymore, and Connors is no longer a ruthless killer with the heart of a lion.