I had the misfortune to turn on the television the other night to something called "It Happened One Christmas." What happended was the kind of abomination you'd normally snap off immediately; a syrupy, about Tiny Tim and Scrooge, but this time set in happy, homey, small-town America with a heroine (Marlo Thomas) who exudes more goo per second than anyone seen before. The ghosts of Christmas past, present and future are combined in one Mary Poppins character with a cockney accent who goes aroung clutching a copy of Dickens as though it's the Bible. Well, if you're the script writer and get that kind of assignment, why not throw everything in the pot? It's got to come to a boil somehow.

The point is, I didn't snap off the set, but indulged in a form of a masochism by watching and wondering how bad TV can get. But many others apparently are not inflicting such torture on themselves. And therein lies this tale. The HUTs, you see, are down, sending tremors throughout the land.

Scattered across the country are some 1,200 little black boxes. Each is attached to a TV set in a home or appartment. These little boxes, called Audimeters, represent power, great power - money, markets, sucess, fame failure. They are the basic instrument by which the A. C. Nielsen Co. measures television audiences. The Nielsen Ratings tell broadcasters, advertisers and program creators who is watching what and when.

Now 1,200 or so little boxes attached to TV sets may not seem like much of a base sample for determining what we see. Particularly not when you consider there are 71.2 million American television homes. In fact, the boxes represent far less than one-tenth of one percentage point of our television homes. But that's the way the ratings are done. As network TV executive Bob Shanks writes in his book, "The Cool Fire," probably never "in history have so few had so much influence over so many."

Dreadful programming notwithstanding, all was proceeding splendidly for network TV. Year after year there have been greater and greater audiences, and more and more money made. Then, sometime last March, a little blip on the curve of progress occured. The Nielsen 1977 monthly Homes Using Television (called HUT, in the trade) - figures were down when compared with the same periods a year ago. Little concern at first. Merely an aberration. But month by month since March, the HUT ratings showed a consistent drop-off from the 1976 figures. From that evidence, it appeared the American television audience may be dwindling at a slow but steady rate.

The sharpest decline in the ratings came in the daytime hours. By November, Homes Using Television levels had registered somewhere between a 6 and 7 per cent drop. No single factor found for what seemed to be a massive TV turnoff by the public.

In the months since March, the networks have been reacting to these figures warily and with some hostility. A considerable controversy has been bubbling throughout the industry.

The figures were suspect. They were caused by seasonable factors. They were affected by the weather. They were biased. They weren't a real trend. Thus, the arguments. Neilsen itself became the target. The networks seized on a true error in the Neilsen ratings two years ago. Then, a number of meters were found to be malfunctioning, a problem that had not been detected by computers. That year, too, there had been a shift in Neilsen's random sample toward a more disproportionate representation in the national sample.

Neilsen stuck to its guns. The networks, it maintained, were blaming the messenger for the message. At the same time, Nielsen began conducting its own studies to see if it could pinpoint what seemed to be happening.

Week by week the issue has been receiving intensive internal scrutiny. The pages of Broadcasting Magazine, for instance, the authoritative journal of the TV industry, have been filled with lengthy accounts of the controversy. Headlines tell the story:

Neilsen Charged

With Short Count

Of Young Viewers

And:

In Search of

Those Missing

Daytime Viewers

And:

The Rules Just

Didn't Apply to

This TV Season

Too many interruptions in the regularly scheduled network programs, too many specials, too much confusion in viewers minds: those were the problems, if, indeed, problems ever existed. A CBS executive explained it by saying:

"For the first time, the American viewer . . . cannot be sure what's on any of the three networks on a given night."

In the last few weeks, a tentative consensus appears to be emerging. Major advertising agencies are saying the evidence for a decline in TV viewing seems persuasive. They agree that available figures show the most significant decline in daytime viewing, with lesser, yet consistent, drop in prime time, too. Broadcasting Magazine quotes a study by Ted Bates & Co. on Homes Using Television levels over the last five years: Prime-time figures are down slightly; in the daytime, Bates found a consistent five-year decline in viewing levels it described "as very serious indeed."

A top NBC executive professes not to be too concerned. But, he adds: "The real answer to the question is: no one knows.Is it the beginning of a trend? No one knows."

The latest word from Nielsen is that the HUT drop seems to be real. Demographic and other data support the idea that the decline is not an aberration but rather part of a long-term trend. The Nielsen date currently show a loss of about 1.2 million households watching TV in the daytime and 250,000 at night.Ralph Clausen, vice president of Nielsen's media research division, suggests that TV viewing levels have peaked and are likely to level off or decline in the future.

He even offers possible reasons: the number of working women is increasing. Family size, which figures in the amount of TV watching, is declining. The number of homes with sets is at the saturation point. The rapid growth of color-TV households - which watch five to six hours a week more than those with black-and-white sets - is tapering off. And, Americans 18 to 34 comprise the only demographic age group increasing in size. Yet that group is the one that contains those who watch TV the least.

They are, of course, the best educated group of Americans in our history.

You'll notice that nowhere in here is there any mention of the programs Americans are being offered. But I'll offer a seat-of-the-pants guess about why so many viewers appear to be turning on, and off - or not turning on at all: they have managed to find something better to do with their time.