After Jimmy Connors had devoured Roscoe Tanner, 6-2, 6-4, 6-3, in the final of the $225,000 U.S. Pro Indoor championships yesterday afternoon. Isaac Stern, the great violinist who is also a longtime tennis buff, went into the dressing room at The Spectrum.

"Jimmy, you played magnificently . . . You didn't miss a note," he said softly, in a heartfell backstage tribute.

"Thank you, Mr. Stern," Connors nodded sheepishly.

"You played for me, and now I'd like to play for you," said Stern. Taking his $250,000 Ranieri lovingly from its case, he played a little day music, just a minute or so, for the street kid from Belleville, Ill. "No special composition, just a little provisation - something nice for Jimmy," Stern explained later.

It was a touching spontaeous show of appreciation from one virtuoso to another. Connors was awestruck. He says the experience gave him goose-bumps.

Connors, who figured to be exhausted but said he was "still pumped-up" instead after his 3 hour 40 minute climb from two sets down Brian Gottfried in a semifinal match that didn't end until 11:30 Saturday night, gave a crowd of 15,673 goosebumps, too.

This was more of a solo recital than a duet because Tanner, who has played so well in beating Ilie Nastase, Bjorn Borg and Eddie Dibbs, offered little of the resistance it takes to make a good match.

Tanner reverted to the ragged ground strokes that used to characterize him. The man from Lookout Moutain, Tenn., did crack 16 aces, but he lost his serve six times. His patches of good serving could not make up for the clusters of unforced errors and errant volleys that denied any semblance of consistency to his game.

Connors contributed considerably to Tanner's regression. While most observers expected a bell-to-bell slugfest between these two hard-hitting left-handers - as was the cast last November, when Connors beat Tanner, 8-6 in a fifth set tie breaker, in the $100,000 winner-take-all final of the WCT Challenge Cup at Las Vegas - Connors smartly eased into the match, taking pace off the ball throughout the first set.

Instead of coming out with all pistons pumping, as he so often does, Connors fed Tanner a variety of shots, mixing power and restraint. This seemed as bizarre as Nolan Ryan throwing mostly change-ups, but it worked superbly.

Tanner appeared stiff, awkward, unable to get his feet moving in the proper synch. He would have liked to answer speed with speed, but Connors - reversing a tactic that has often been used against him - didn't give him much speed to work with.

"I've got a little mixture in my game now that's just come about the last six months," Connors said. "I don't feel I have to slug the ball all the time. I can't because these balls (orange Spalding Australians) are quite heavy, and they stay low on this court (a medium-fast "Supreme Court" carpet). I have to wait and pick my shots to hit through the ball."

Connors tactics were also sound because he was trying to pace himself in the best-of-five-set match. He knew he might get tired because he didn't get to sleep until 4 a.m. after his 3-6, 4-6, 6-3, 6-2, 6-0 triumph over Gottfried. In that match, he threw caution to the wind and started hitting out when he was two sets down, going for the lines with savage shots in the inimitable style that makes him the most exciting player in the game.

"I'm no afradi. Maybe that's the difference between me and some of the other guys. I figure if I'm going to lose, I'll do it playing the game the way I think it should be played - eager and all out," he said of the Gottfried match.

"I went back to the hotel after that, got something to eat, watched a little TV. I relaxed real well: I wasn't sleeping, but my body was resting. I got up eager to come back out and play, and started out riding the crest of the wave. I guess I didn't have time to come down."

After Tanner held his serve at love in the first game, serving two aces. Conners held serve from 0-10, saving four break points. Tanner served an ace on the first point of the third game, then missed four first serves in a row to fall behind 15-40, and punched a low forehand first volley long after saving one break point. That game foreshadowed what was to come.

Conners held after one break point for 3-1, broke again as Tanner fell into a rut of making errors, and accelerated from there.He gradually opened the throttle, hitting harder, and made more of the aerobatic, almost bionic shots for which he is famous.

"He just played too well today," said Tanner. "On the dead run he was hitting balls very hard and very accurately, and that's what I think makes him probably the toughest guy in the world to beat . . . When it's a big match, that's how he plays."

Tanner was consistenly late on his shots, a fact he attributed to Connors' preference for hitting the ball flat. "Nastase, Borg and Dibbs hit with a lot more topspin, so the ball is coming a littl slower through the air," he said. "Jimmy hits flat, so the ball comes faster and stays lower.

"It's interesting because I used to have a lot of trouble handling the heavy topsin. Now I'm used to that, but I have to react a little quicker to the way Jimmy hits the ball, get my feet in place and my racket back."

Connors held from 15-40 in the sixth game of the second set, and got the only break in the ninth game. Tanner double-faulted to 15-40, saved one break point with an ace, then was wide with a forehand first volley down-the-line off a return that surprised him by coming back even harder than he had served it.

Tanner lost his serve to 1-2 in the third set on three volley errors, and now Connors was rolling. He was broken only once in the match - serving for it at 5-2 - but immediately broke Tanner again to close it out.

Connors finished January with earnings of $199,000, which he called "a pretty good month." He collected $100,000 for beating Borg in the final of the Colgate Grand Prix Masters, $64,000 as runner-up to Borg in last weekend's "Pepsi Grand Slam," and $35,000 for winning here.

South African Davis Cuppers Bob Hewitt and Few McMillan, who won the Masters doubles, spilt $11,500 for beating Sandy Mayer and Vitas Gerulaitis in yestersday's final, 6-4, 6-4.