If you telephone friends some evening this week, there is a much better chance than, say, a few months ago, they'll be at home.

As perhaps never before, Americans have become couch potatoes.This finding comes from an outfit that actually checked the whereabouts of Americans by calling about 4,000 households in the past month. And in one of those weeks it found only 9.9 percent of household heads weren't at home.

Albert Sindlinger, whose researchers made the calls, said the percentage is the highest he has found in 36 years of market testing. For comparison, nearly a third of breadwinners were out somewhere last Labor Day weekend.

The findings correlate with and explain the complaints of retail merchants, carmakers, airlines and others that customers just can't be found. Staying home, sitting on the couch, so to speak, has become an "in" thing everywhere.

There is great commercial significance in the percentages. If 91.9 percent of household heads - they're the ones with the money - are at home, then 141.62 million of them aren't shopping, dining, traveling or negotiating for a car.

It is true that during this time of year Americans tend to spend more time at home, if only because of bad weather and the need to pay Christmas bills. This year, two other factors, war and recession, have been added.

As you might have guessed, the record at-home period was the one in which the war began. In the period Jan. 17-21, said Sindlinger, the number of at-homes rose by more than 20 million heads of households.

"They were affixed to their television sets, watching the first war to be exhibited on television," said Sindlinger from his office in Media, Pa., where Sindlinger & Co. staff have been calling homes daily since 1955.