Jimmy Connors and Ivan Lendl, winning easily today, will take their thunder sticks to the Stadium Court again Sunday afternoon with the U.S. Open tennis championship the prize.

Flustered only once, the second-seeded Lendl put down surprising Jimmy Arias, 6-2, 7-6 (7-3), 6-1. Then Connors, the third seed, limped on a sprained little toe through the last games of his victory over Bill Scanlon, 6-2, 6-3, 6-2.

"It's okay," Connors said after dipping his left foot in ice for a while. Four times the Open champion, Connors last year beat Lendl in four sets for a championship he first won in 1974--when Lendl was a 14-year-old boy in Ostrava, Czechoslovakia.

Six other times, Connors has won Grand Slam championships. Lendl, 23, has won many titles but never one of the big ones, his two defeats in such finals giving rise to talk he doesn't have the right stuff to take the last step to greatness.

"I'm no amateur psychologist," Connors said when someone pestered him to plumb the depths of Lendl's mind. "I have enough problems of my own."

As for Lendl, he said, "No," when asked if he were nervous about Sunday's work.

Nor should he be all atwitter. As good as Connors has been this fortnight, not losing a set, Lendl has matched him in perfection. They come to the Stadium Court Sunday afternoon a pair of aggressive warriors who have pounded 12 opponents into numb submission. Connors plays, as he says, for blood, saving nothing back as he slugs winners from every angle. Lendl is cooler, a dour personality, but no less the blunt instrument of pain.

Today, with sledgehammer forehands, Lendl reduced Arias to a mere nothing. Arias, 19, won the Italian Open earlier this summer, was the ninth seed here and became the youngest men's semifinalist since the Open first admitted professionals in 1968.

The youngster surveyed the wreckage of his defeat and could offer only slight suggestion that it might have been different.

Arias said, "I sensed Lendl getting tight when I broke him (and needed only a single point, at triple set point, to win the second set).

"Since he hasn't lost a set and hasn't won a Grand Slam tournament and everybody keeps reminding him of these things, he might have gotten a bit nervous."

Trailing, love-40, on his serve at 4-5 in the second set, Lendl did, in fact, seem in disarray. He had double-faulted three times in his previous seven service points, twice scowling at the electronic eye that calls the service lines these days.

Lendl then ripped a forehand past Arias, scored with a first serve to the youngster's backhand, caught the line with a bold forehand and closed it out with a laser-beam ace and another unreturnable first serve to the backhand.

"At 30-40, I hit a risky forehand and caught half the line with it," Lendl said. "And then I got away."

In 18 straight sets now, Lendl has been invincible. The electric moment of today's match came when Arias, brash as youth, crashed a forehand into Lendl's wheelhouse. The sound of the dueling forehands was that of small explosions. Lendl's won the war unconditionally. Besides which, he served 11 aces, increasing his tournament lead in that important category to 54.

That serve carried Lendl in the second-set tie breaker. Arias, who has a 16-5 record in tie breakers, led this one at 3-2 when Lendl suddenly won four straight points, the first two set up by strong serves, twisting Arias into compromising shots.

"I seemed to fall apart," said Arias, who came here two weeks ago as a clay-court champion eager to prove his mettle on fast courts. His unexpected advance to the semis was created by an all-court game featuring a forehand thought to be a near-match for Lendl's.

But it was an attempted forehand that foreshadowed the end, for with a 2-1 lead on his serve, Arias mis-hit a forehand, squibbing it high off the frame and into the potted plants at courtside. "That gave me a chance," Lendl said. From there on, the match was all Lendl's. He had passed his moment of peril and was back on balance. About then, the threads holding Arias together came undone. It happened when Arias needed a point to break Lendl's serve in the first game of the third set--only to lose it on a debatable line call.

"I let a call really bother me," Arias admitted later. "The way the umpire talked to me upset me. I said the ball was five inches out. He said, 'Well, the linesman called it in and I think maybe it caught the end of the line.' I got so upset . . . I lost my concentration."

So Lendl moves on to another match with Connors, who holds a 10-3 edge in their meetings the past five years. Since Connors won their first matches, Lendl has won three of the last five, including a straight-set victory at Montreal last month.

But that was Montreal last month, not Flushing Meadow on a Sunday afternoon in September. Connors left Scanlon muttering today. The conqueror of John McEnroe, Scanlon was down, 3-0, before he remembered to take a breath.

"He might not have expected the barrage right away," Connors said. Whether with his serve, which was wicked, or with his thundering ground strokes, which left Scanlon wondering how anybody can be that good, Connors turned Scanlon into a hang-dog loser quickly.

Even limping through the last set, Connors was so much in command that maybe half the estimated 15,000 spectators had left for home by match point.

Johnny Carson, the TV guy, split early in the third set. He didn't even leave a guest host.