By now, most TV fans know the mechanics involved in becoming a contestant on the TV game shows. (The majority of them are chosen at random from the studio audience). But what about the celebrity contestants? How are they selected?

We put the question to a woman who knows about these things, Debbie Wiener, a charming and personable 28-year-old who serves as talent coordinator for Bob Stewart Productions, the producer of "The $20,000 Pyramid" on ABC, it's sister syndicated nighttime version "The $25,000 Pyramid" and "Shoot For The Stars" on NBC.

"First, I'd like to point out that there are three separate units in our company," said Debbie. "Programming, which is headed by producer Anne Marie Schmitt; contestants, under the supervision of Edith Chan, and celebrities. That's my department. I book the guests for all three programs.

"The daytime 'Pyramid' and 'Shoot For The Stars' both use two contestants and two celebrities per show five days-a-week (all taped in one day). The nighttime 'Pyramid' tapes six shows in a day, with six celebrities each doing two different programs.

'"Pyramid' is easy to book simply because out producer Anne Marie started the ball rolling before I joined the company four years ago," said Debbie, taking a break from the W. 58th St. ABC studios where 'Pyramid' is taped.

"The show has become so popular and is such a challenge for the guests that they come looking for us. It's not the money that draws them to do the program (celebrities get $1,000 per day's work on the daytime entry and $1,500 a day for the nighttime shows) as much as the excitement and the fun of playing the game," she said.

In searching for new faces, Debbie said she watches all the talk-variety shows and looks for people who are not deadbeats. "I look for exciting people, not those who are going to bury their heads in their laps, afraid to shwo emotion. This type would never want to do a game show anyway," she added.

Are there any requirements for guests? "Well, they must watch the show and be familiar with the way it's played. Also, they must be the type that the audience will easily recongize. That's why we use so many TV personalities. People recongnize Charles Nelson Reilly more easily than they would a Don Murray who has made a slew of films. Many of our regulars include Soupy Sales, Anita Gillette, Tony Randall, Pat Carroll, Peggy Cass, Vicki Lawrence, Jack Klugman and many others."

Debbie then started to recall some past experiences. "Paul Lynde did our show once and was terrific. I remember Charles Nelson Reilly got so excited that when he backed up he fell to the floor and his leg went way up in the air. What a sight!

"Lee Meriwether admitted to me that she forgets to breathe when she's doing our show. She hyperventilates and literally gets out of breathe and faints. Peter Lawford was a riot. After winning a round, he got so stirred up that he went chasing host Dick Clark around the stage shouting, 'I did it, I did it!' He just went bananas."

Asked for the best players, Debbie replied, "That's hard for me to answer because guests can have their highs and lows. One day, their energy level can be very high and another time it's way down. Sandy Duncun, for instance, is a very good player. But there are days when she loses every match. But once she gets going, there's no stopping her.

"You really don't need a college education to play our games," said Debbie. "All that's necessary is a certain amount of knowledge of what's going on in the world. But don't get the idea that out shows are easy to do. Taping five or six of them the way we do all in one day is an extremely exhausting schedule. But it's a lot of fun."

Debbie, who is a game player freak at home, was graduated from Western Maryland College, where she studied to be a social worker. "I thought the world was waiting for me to take care of all those poor unfortuneates. I never dreamed I'd be working in TV taking care of celebrities."

Would she ever step in front of the cameras? "I'd probably fall to pieces," she said with a sigh, as she rushed off to keep a date with another celebrity, this time it was her fiance, Bill Hefferan, whom she planned to marry the very next day.