Quarterback Joe Theismann once remarked that playing the Dallas Cowboys was a "Sunday stroll" compared to a tennis match he once had with former basketball star John Havlicek. Theismann spoke of extreme pressure that "comes from within." Theismann is not Jimmy Connors - just another hacker like the rest of us who has experienced that primeval terror of standing alone on a tennis court staring at a foe 78 feet away.

Unlike the continuous movement in basketball and soccer, tennis is punctuated by long pauses that give you plenty of time to dwell on the missed overhead or double fault that cost you a game. This is why you can rally beautifully during a warmup, then play miserably during a match. This is pressure from within.

Take mental stock of yourself. Are you trying to play like Ilie Nastase when you can't even get your first serve in? Are you trying to impress other players with your outrageous shotmaking? You might be a serious candidate for choking up.

Start playing simply to win. Try to beat your opponent as soundly as possible and not just coast by. Decide on a game plan and stick to it for at least one set. When the match gets tight and your stomach does too, forget about your opponent, your mortgage and your job and just concentrate on the tennis ball. Play within yourself. Tell yourself you are mentally and physically tougher than your opponent. Play with confidence bordering on arrogance. You're entitled to a butchered overhead or two; just don't let them affect your game. Also don't let your opponent intimidate you with his three rackets and his Italian tennis togs; nor should you underestimate the player wearing blue jeans.

Q - I have noticed some opponents try to out-psych me by continously asking if I am ready after a five-minute warmup. What should I do?

A - Take control of the situation. Say that you intend to warm up all your shots. When you are ready take the initiative by spinning the racket and asking him to call it.

Q - I feel more pressure playing a supposedly inferior player than someone of my ability or better. Why?

A - You are probably playing more out of a fear of losing than just trying to play your best to win; the result is tentative and poor play. Change your attitude to one of confidence. Forget about your opponent; play the ball instead of the player.

Q - One of my opponents always beats me when the score is really close, but I sometimes beat him by a wide margin if there are no stakes. How is this?

A - Evaluate your overall relationship with this person. He could be getting to you in other ways. Maybe he is simply mentally tougher in crunch situations. You must simply resolve to get tougher next time and not succumb to the pressure.

Q - I can sometimes build up a comfortable lead but then not be able to put a match away. Why does this happen?

A - You could be playing out of a fear of winning. You want to display your talent and tennis mastery on the court, but you can't stand being the bad guy who crushed a friend. Thus you prolong the match and lose it.

Q - What's the best way to relax before an important match?

A - Go see the Rocky Horror Show the night before. Or anything else that will take your mind off tennis. Don't sit around watching other matches before yours is scheduled, since this gives the pressure a chance to mount. CAPTION: Picture, PLAY WITHIN YOURSELF, WITH A CONFIDENCE THAT BORDERS ON ARROGANCE. By Craig Herndon.