Arthur Ashe's favorite sweater, which he wore to the Spectrum today, is a blue and white one bearing the words "Faded Glory." He should put it away, for he is not ready for it quite yet.

In a 3 1/2-hour struggle more memorable for the drama of a great comeback than for the quality of the tennis, the 35-year-old Ashe revived himself from two sets down and 3-5 in the third today to beat younger, quicker Vitas Gerulaitis, 1-6, 4-6, 7-6, 6-4, 6-4, in the semifinals of the $225,000 U.S. Pro Indoor Championships.

In Sunday's final, with a $40,000 prize at stake, Ashe will play Jimmy Connors for the first time since 1975, when he upset him with a tactical masterpiece in the Wimbledon final and went on to claim the No. 1 world ranking.

Connors, the defending champion here, returned serve savagely tonight in eliminating last year's runner-up, fellow left-hander Roscoe Tanner, 6-3, 6-3, 3-6, 6-1.

Tanner had not lost his serve since the opening game of his first-round match against Vijay Amritraj. He was never broken in overpowering Tom Leonard, Eddie Dibbs, and the highflying teen, 19-year-old John McEnroe, to get to the semifinals.

But Connors was devouring his favorite delivery, a hard slice to the left-handed forehand. And the rockets launched from Connors' slingshot of a steel racket crumbled the foundations of Tanner's serve-and-volley game.

Tanner served 16 aces, but never seemed really in the match after Connors broke him in the seventh and ninth games of the first set, and in the sixth game of the second set with a backhand down-the-line return winner off a bullet first serve.

Connors suffered one lapse, losing eight straight points and 13 of 14 in falling behind, 1-4, in the third set, but soon reestablished his superiority, hammering out a 5-0 lead in the fourth set.

"I think that's the hardest he's hit the ball in the last few times we've played," said Tanner, who has lost six meetings with Connors since beating him twice in 1976. "I tried to mix up y serves, but he was really nailing the forehand return every time, and that's the side I like to go to."

Some of Connors' returns -- notably the forehand winner off a blistering first serve that gave him the demoralizing break to 2-0 in the fourth set -- were blurs.

But it is unlikely that Ashe -- who played cleverly and doggedly despite getting only 49 percent of his first serves in court and double-faulting 14 times -- will make the the mistake of playing "hardball" with Connors. He knows that Connors trumps pace with pace and will likely try to softball him as he did in that Wimbledon final of '75.

Like a pitcher who learns control and change-ups when he can't fling the ball past hitters for nine innings anymore, Ashe has tempered a game that was once all-out aggression. He still has the "high hard one" for when he needs it, but he cunningly changes speed and spin, crossing up fast ball hitters like Gerulaitis, 24, and Connors, 26.

His guild and cerebral approach tto a game he once played with instinctive abandon was well domonstrated in the uphill victory over Gerulaitis, which delighted an enthusiastic crowd of 8,811 spectators.

This match -- a long climb back from nowhere against odds that seemed longer to everyone else than they did to him -- in many ways symbolized the last 12 months for Ashe.

He was No. 257 in the computerized world rankings of the Association of Tennis Professionals when he started a comeback last January. Heel surgery sidelined him most of the 1977 season. Few thought he would attain even his short-range goal of getting back among the top 15 players in the world, to say nothing of approaching the No. 1 status he earned in 1975 by slowballing Connors to a stunning defeat in the Wimbledon final.

But Ashe has already clawed back into the top 10. He reached the final of the Colgate Grand Prix Masters playoff two weeks ago, blowing a 4-1 lead in the final set and two match points against McEnroe. He has played exceptionally well in ousting Guillermo Vilas, Brian Gottfried and Gerulaitis here, and could establish throughout 1979 with another strong performance in the final.

Ashe has accepted reluctantly the role of old warhorse reclaiming faded glory.

"I decided just this morning that I was going to go along with that, because there's nothing else I can do," he told reporters ready to praise him as a splendidly refurvished antique after the match. "You guys keep bringing it up. I guess it makes a good story."

Indeed it does, especially when Ashe spices the plot with a display of physical and psychic stamina as he did today.

When Gerulaitis served for the match at 5-4 in the third set -- after Ashe had lost his serve in the fifth game with three double-faults, including the last two points -- he came back from 15-40 and was twice within two points of the match at deuce.

But Ashe did not look at this as the brink of disaster, just as he never looked at his return to the international circuit as a quixotic quest for faded glory.

"At that stage, even though he's only two points from the match, I'm only two points from the break back to 5-5. It's that close," Ashe said.

He got to advantage as Gerulaitis netted a forehand scoop off of one of numerous drop shots that eventually took their toll. He got the break with a sharply angled backhand cross-court passing shot off another all-court, cat-and-mouse point.

Two games later, they were into a best-of-12-point tie breaker. Ashe took the last two points on Gerulaitis' serve to win it, 7-4.

First he chipped a backhand return of a second serve and scooted in to the net -- a tactic he used with repeated success after overhitting numerous returns in the first two sets -- and won the point with a smash.

Then he smacked a forehand return that skipped off the net cord. Gerulaitis made a marvelous reflex volley, the ball fluttering just over the net to Ashe's left. He got to it and whacked a backhand down-the-line winner, vaulting over the blocks used as ballast to secure the net post.

Few knew it then, but the tide of the match turned on that tie breaker.

Ashe, whose metabolism starts functioning properly only after noon ("I'm an afternoon and night person, not a morning one"), stopped sleepwalking, and started hitting some of the shots that enabled him to put Gottfried away at 10:30 Friday night.

Meanwhile Gerulaitis started playing more tentatively. "He moved back a couple of feet to receive serve in the last two sets. That was a mistake," said Ashe, who mixed flat and spin deliveries to keep Gerulaitis out of rhythm. "His whole demeanor changed a little bit. He got defensive. He wasn't playing to win. He was waiting for me to make an error.

"I mixed my game up and played him the way I wanted to play him. You can't go through Vitas because he's too quick... one of the two or three quickest players on the tour. The harder you hit the ball, the worse off you are unless you have an outright opening, bacause he'll get to the ball and knock it off. He loves speed, just eats it up."