There are Sunday afternoons when your Eastern forehand is clutching a cold aluminum can and the nearest tennis court is flickering on the tube in front of you.

There are two reasons, besides the chance to drink beer, for watching tennis on TV. One is to be able to surprise everybody at the courts later that afternoon by casually mentioning some detail, such as: "McEnroe's first serve was off but he beat Gerulaitis 7-5 in the third." The other is to get a bit of video transference.

We just made that phrase up. But the phenomenon really exists. Watching the pros and then running straight onto the courts has lifted the game of more than one player of dubious natural gifts (including one of the authors of this gospel, but we're not saying which one). Every successful athlete learned most of his fundamentals by imitation; in tennis, we often have to get that from television.

Besides the general feeling of fluidity and mastery of the ball that one can pick up from watching a pro match, there are ways to study particular parts of the game at its highest levels. When the camera is behind the player receiving service, study his footwork for a while. Forget about the ball and watch how he prepares for service; then see how he positions himself for the next ball.

Study his backswing and service return-is it a full swing or a block return? Try imitating it the next time you face a hard server.

Try to notice that the difference in how the pros play clay and hard courts. Blackcourt artists such as Harold Solomon don't come in often but their feet are in perpetual motion. Watch how the pros often clear the net by five or even eight feet, while amateurs too often try to hit skimmers. Bjorn Borg doesn't even mind hitting moonballs - just to keep the furry little thing in play.

Q - The pros all seem to have different ways of stroking the ball, but they are all consistently better than amateurs. What are some of their secrets?

A - Apart from natural talent and years of hard work, one thing every pro does is meet the ball early. One survey of the top 200 players showed that they hit the ball much farther in front of their bodies than most of us do - and that the top 50 made contact farther in front than the next 150. This increases control and power. Certain fundamental rules really do work.

Q - How can a top player like Harold Solomon get away with such a pitty-pat serve?

A - Because he places it so well and then is so tenacious at retrieving the hard returns he gets. Solomon compensates for lack of offensive power with superb defensive play in his groundstrokes.

Q - I have noticed that the pros warm up for only five minutes before a match. Is this enough for them?

A - No. They have already warmed-up for 40 or 50 minutes on a side court with another pro. They practice all their strokes beforehand and may even play a practice set.

Q - Why are there fewer upsets in women's tennis than in men's?

A - Because there are fewer variables. Women's tennis depends more on consistency than power. A male player such as Roscoe Tanner can on a good day beat Jimmy Connors because of his overwhelming serve and volley. But even hard-hitting Betty Stove can't serve enough unreturnable balls to overcome Chris Evert's steadiness.

Q - Do tennis commentators such as Bud Collins, Tony Trabert and Donald Dell know what they're talking about?

A - Yest. Trabert won the U.S. Open twice and Wimbledon once. Dell was once ranked sixth in the United States and fondly remembers beating Rod Laver when he was 14. He also captained the Davis Cup team for five successful years. Bud Collins is a mere journalist but an excellent amateur player who probably knows more about tennis technique than any other non-proaround. The only strange thing is that he likes to play barefoot and does not wear socks in the winter.