SOMETHING IS happening in America. Television viewing is going down. Nielsen said daytime viewing was off by 6.4 per cent, and 3.1 per cent at night. We're talking about millions of people now and the big question is where have they gone and what are they doing if they aren't watching television?

I decided to call Plotnick, who heads the "Bureau of Missing-TV Viewers," an organization set up by the networks to find out what has happened to them.

Plotnick wouldn't tell me how he got the names of the people who weren't watching TV, but he hinted he has a very close connectionwith the CIA that knows exactly what every American is doing.

He had a list of names and addresses and said I could come along and see for myself how he operates.

The first house we visited belonged to a family named Peters. Plotnick was very polite.

"Pardon me, ma'am, but I understand you're TV set is off. I was wondering if you could tell me why?"

"Who on earth told you that?" she wanted to know. "The children have it on right now. Come in and I'll show you."

We went inside and found four children in the living room. The set was on, but instead of a picture on the screen the kids were playing hockey with four dials.

"But they're not watching anything?" Plotnick asked.

"No," the mother said. "They haven't looked at a show since they got this Pong game for Christmas. It's a marvelous invention. They can play hockey, tennis, tic tac toe, race automobiles, shoot down airplanes and sink submarines."

"But that wasn't what television was invented for," Plotnick said. "It was invented to transmit pictures and sell products to the American public."

"I know," said the mother. "The kids saw the Pong game advertised on televsion and insisted we buy it. Frankly it's a lot more fun than 'Kojak' and it's been a lifesaver in our family."

Once we were out in the street Plotnick wrote some notes on a piece of paper. "This is going on all over America. The damn kids are using TV to play games. They don't realize there are millions of dollars of commercials at stake. They would rather play pin-ball on a TV screen."

The next house we went to belonged to the Strathmores. Mrs. Strathmore admitted they didn't watch television anymore because their set was broken.

"Alfred threw a beer bottle at Howard Cosell one night and smashed the screen."

"Why didn't yoy have it repaired?" Plotnick wanted to know.

"I did and the next Monday he threw another beer bottle at Howard. How many TV screens do you want me to buy?"

Plotnick was disgusted.

It was about 10:30 at night. We had visited houses where the neighbors said the inhabitants had either gone to "Star Wars" or "Close Encounters of the Third Kind," homes where one or the other person was in the process of getting a divorce, and couldn't watch TV because they were spending all their time on the telephone, and several where people admitted they had gone back to reading books.

"Each household we've visited," said Plotnick, "represents 1 million people."

Our final call was at the home of the Pells (not their real name). It took some time for Mr. Pell to answer the door. He was in his bathrobe. Plotnick asked him why he wasn't watching TV.

"We used to be avid TV watchers," Pell said. "But then Judith bought 'The Joy of Sex' and you know something - we discovered it was more fun than watching television. We're on page 85, and I don't think we'll get through it until the summer reruns."

"And you'd rather do something dirty than watch TV?" Plotnick said bitterly.

"I guess," said Pell, "it's which 'Behind Closed Doors' you want to get involved with."