It used to bother Jimmy Arias that Tracy Austin and Andrea Jaeger and Kathy Rinaldi got all the praise for being the super teeny-boppers of professional tennis.

The experts figured Arias would be 19 or 20 before he become strong enough to contend. But patience isn't one of Jimmy Arias' long suits and yesterday the 17-year-old from Grand Island, N.Y., upset Jose-Luis Clerc, the defending champion and fifth-ranked player in the world, in three sets in the D.C. National Bank Classic.

"I'm catching up with them physically now," Arias pronounced afterward. For the first time in his two-year professional career, Arias will play for a major tournament title.

His opponent tonight at the Rock Creek Stadium court will be Ivan Lendl, the tournament's top seed and a man who has won more matches than any other professional tennis player in 1982. Lendl, who easily defeated fourth-seeded Yannick Noah in the second semifinal, will be the odds-on favorite to win. But Arias will be the overwhelming crowd favorite, a fact of which Lendl is very aware.

"Obviously, everybody will be behind Arias," Lendl said. "I fully expect that. It makes me tougher and more determined to prove to everyone that I can beat him anyway."

Asked how he deals with playing the villain's role, Lendl replied, "The question is whether he can handle the pressure if he starts winning."

Of all the players on the professional tour, Lendl is probably one of the least likely to have a letdown in a big match. He has reached the final 12 times in 14 tournaments this year, winning eight.

"I want to beat him as bad as guys who are ranked above him," Lendl said of Arias, ranked 79th in the world.

Clerc, last year's champion, said Arias will beat Lendl if Arias plays as well as he did yesterday. Clerc may have gone out on a limb with that statement, but it is obvious Arias no longer must wait two or three more years before he can compete with players ranked in the top 10.

Arias, at 135 pounds, is still not as fast or as strong as Clerc, Noah and Lendl. He isn't as consistent from the back court as Mats Wilander, Sweden's new teen angel who is six days younger than Arias. But Arias, in winning four matches this week, showed he can do a lot of things well already.

"Jimmy's footwork and anticipation are way above that of the normal player," said Arias' coach, Nick Bollettieri. "Jimmy's backhand is getting so good now that he doesn't have to worry about running around it unless he just wants to. Wilander is as steady as anything and he's in better physical shape. But Jimmy can do a lot more with the ball."

Some parts of Arias' game already are mature. His cross-court forehand into the ad court--a somewhat odd shot for a right-hander--is devastating. "Jimmy'll club you with that shot," Bollettieri said. He did several times yesterday.

"I can keep a guy guessing and off balance with that forehand into the ad court. My backhand, they can read . . . move around it and blast a forehand," Arias said. "I developed it as a shot to keep people off of me. But it's turned into an offensive weapon."

Before the Lendl-Noah match had been decided, Arias was asked about playing one or the other tonight. He replied, "I'm going to have trouble against either of them."