After Harold Solomon, "The Mole," had worn down and out stroked Dick Stockton, 6-4, 6-4, 6-2, in the quarter finals of the U.S. Open Tennis championships, someone who had never seen him play asked Solomon if he ever gets impatient.

"Sure. That's when I lose," said the 5-foot-6, 140-pound pro from Silver Springs, Md.

Solomon does not intend to lose patience when he plays streaking Guillermo Vilas, one of his toughest clay-court rivals, in the semifinals of the Open Saturday at the West Side Tennis Club.

The winner of the match will play the victor of Jimmy Connors vs. Corrado Barrazzutti for the men's singles title and $33,000 on Sunday.

Vilas - who has won 37 consecutive matches over seven tournaments, 44 in a row on clay going back to his triumph in the French Open - generally is considered the fittest player in the game.

But that reputation, and the fact that Vilas won five Grand Prix tournaments on successive weeks this summer, something no one else has accomplished, does not worry Solomon. "He's a big, strong guy," Solomon concedes "but he gets tired just like everybody else."

Vilas has a 6-4 career record against against Solomon, 1-0 this year, but Solomon, 1-0 this year, but Solomon has won three of their five meetings on clay and both were best-of-five sets.

"I think I can outlast him in five sets," said Solomon, who did so in a five-hour match the first time they met, in the French Open of 1972.Solomon won their last clay court encounter, in the quarters of the French last year, 6-1, 0-6, 7-6, 6-1.

Solomon's last two victories here have come over players who like to get to the net as much as possible, Italian Open champ Vitas Gerulatis and Stockton. He stayed back and beat them primarily with his passing shots, controlling both matches with attacking shots from the backcourt.

"I just try to keep the ball deep. I'll go for the shot if I get it, but I'm not going to press it," he said. "If I got a short ball I'll go for a winner. If I don't, I'll wait until the opponent comes in on a bad shot or makes a mistake."

Vilas, the Argentinian lefthander who spilt finals with Solomon in the 1974 and 1975 Washington Star Internationals, plays the same kind of attacking baseline game, hitting with heavy topspin off both sides in long baseline rallies, carefully waiting out his chances to become the aggressor.

Solomon likely will try to open up the court with his two-fisted backhand - of which he can hit hard, loop, shovel little angles or drop shot - and go for winners mainly off the forehand.

Two keys for him undoubtedly will be to get a high percentage of first serves in - he did this against Gerulaitis and Stockton - so that Vilas cannot attack his weak second serve, and to keep the ball deep. He also must answer the drop shots that Vilas probably will employ in attempts to bring him to the net and exploit his deficient volley.