Since it costs each of the television networks about $2 million a year to avail itself of the A.C. Nielsen Company's TV ratings service, you can imagine how thrilled the networks were when the high-priced messenger showed up at the door with bad news for all three of them.

The bad news, which surfaced last month, was that, since April, Nielsen's National Television Index has shown a steady decline in HUT levels - that is, in the number of Homes Using Television. Prime-time viewing was reported down by 3 per cent from 1976 and daytime viewing was down by a more alarming 8 per cent. Clearly, this was what nobody wanted to hear.

So, what do the networks do when they learn that fewer people are watching television? Do they search their souls for ways to make TV programming better and lure the viewers back? No, you fool. They all gang up on the ratings service and try to prove it wrong.

At times like these, CONTAM springs into action. CONTAM is not, as it may sound, a secret government intelligence organization hidden away in a bureaucratic cranny. CONTAM is the Committee on Network Television Audience Measurement, and its members are executives in the research departments of ABC, CBS and NBC. CONTAM monitors the monitor who mission is to find the fatal flaw in the Nielsen system that resulted in those unthinkable dropoff statistics.

To this end CONTAM has dispatched agent Gale Metzger, himself a former Nielsen executive and now head of statistical Research Inc. of Princeton, N.J., to bottom, locate the proper nail and hit it right on the head.

Metzger has covered this beat before.The last time Nielsen reported a substantial viewer dropoff, in late 1975, Metzger got the case, discovered a guilty wrinkle in the composition of the Nielsen sample, and saved the day for the nets. At this very moment, Metzger is in Dunedin, Fla., poking around the central computer that collects all the Nielsen data from around the country.

A quarter of a million prime-time viewers are missing! Metzger must search out the clues to this mysterious disappearance; what the networks hope is that it will all turn out to have been an illusion.

The Nielsen people are not happy to open their secret installation to an outsider, even if he is a former insider. "It's an uncomfortable position to be in," says Nielsen spokesman Bill Behanne. "We feel, based on looking at our system, that there has been a real decline in number of viewers."

To measure the size of television audiences and thereby help determine what advertising rates stations and networks charge, Nielsen tabulates input from meters affixed to TV sets in 1,170 scientifically selected U.S. homes and, to a lesser extent, from 2,400 "diaries" (viewing logs) distributed at random. Networks and stations pay Nielsen for access to the results - the "numbers." In 1976, they pay Nielsen a total of just over $25 million.

Complaints about the unfairness of it all are as old as the Nielsens, which date back to radio and which became the national TV standard in the mid 's 50s. By this time, if you don't like the Nielsens, that's just tough. Still, people - especially those whose ratings are low - continue to protest. Joining this chorus recently was whirlwind producer Norman Lear, who announced resumption of production on his syndicated "Fernwood 2Night" show, renamed "America 2Night," even though ratings had not been high first time out last summer.

Lear says there is a "cultural lag" between Nielsen's data-gathering apparatus and "public appreciation" of his show, which he claims drew 12,000 "impassioned" letters within three weeks of its demise. "There's a a whole segment of this nation, like college students, that Nielsen considers 'transitory,'" Lear says. "These people are not metered. They are sent no diaries. Those are the hundreds of thousands of kids who were among our viewing audience."

Under-representation of single people, especially males between 18 and 24, is a flaw of the system. Nielsen virtually admits it. "Those who live in group quarters are excluded," says Behanne. "To the extent that that is true, it is true. Also excluded are people in bars, jails and hospitals.

"Dick Cavet would have the same complaint as Lear has. But the fact is, the percentage of our population that is single, between 18 and 24 and resides in group quarters, is so small, that even if they were all watching the same thing at the very same time, it wouldn't make a bit of difference to any God-damned rating there is, and that goes for Dick Cavett, too."

It's also been said that blacks and other minorities are under-represented in the Nielsen sample and that member of minority groups are more reluctant to let a Nielsen "box" (meter) into their gomes than other people are. Normally Nielsen pays a "cash gift" of $25 to those who consent to being wired to dear old Dunedin and then an additional $1 per month per TV in the house. For ethnics, these rewards may be larger.

"In specific areas in specific cities, in the real bad news areas," Behanne says, "the cooperation rate is less. There's no ethnicity or racial type of characteristic to these people - just a geographic one. To increase cooperation, it does help if you increase payments."

Another frequently heard criticism: that Nielsen is slow to react when families add new TV sets to their homes so that they may be watching a show unbenownst to the meter. Behanne says one meter covers all the TV sets in a house but concedes the family must notify Nielsen in order to get newly acquired sets hooked into it. A field staff functionary is supposed to visit each Nielsen family five times a year to make sure they aren't doing any vagrant viewing.

What compels a Nielsen family to go to the trouble to notifying Nielsen that there's a new set in the house? "I reward you handsomely," says Behanne. How much? "A quick five bucks. This time of year is really swell for us, with people buying sets as Christmas presents, and yet you'd be surprised how many people in sample will notify us ahead of time, so that when the kid opens the set on Christmas morning and plugs it in, zappo, he's on line."

At the networks, the research chiefs are not bad-mouthing Nielsen these days, not publicly anyway, and they say the HUT level drop is but a passing ripple, even if they have sent a secret agent to Florida to investigate it.

"The whole thing may be going away," says Marvin Mord of ABC. "In the last few weeks, the prime-time level has been coming back up. And we said all along that statistical variations within the Nielsen sample will occur as television reaches a point where penetration has pretty much peaked."

"I suppose it could be considered an annoyance, an embarrassment, a blow to the corporate ego" says Arnold Becker of CBS. "Our vocal critics, all those people who hate television and say it's polluting the minds of Americans they can look at the HUT dropoffs and go 'HA HA HA, look what a lousy job you guys are doing.'

"Well, this may sound absolutely outrageous, but in my opinion, the average popularity of television programs actually increases every year; the shows that survive are so very popular that it's hard for new shows to break in, so you have a lot of programs being taken off the air. I believe there has been a long-term increase in quality."

"It isn't as if the industry is not operating at a very substantial homes level," says Bill Rubens of NBC. "In 1956 the average TV household spent 34.3 hours viewing television per week. In 1977 it's 44.4 hours. Obviously a lot of time is being spent watching television. Just not enough."

All three top network researchers deny that they are pressuring the Nielsen system to give them the good news they want, whether it's true or not, though it would seem they are going to a lot of trouble to disbelieve a system they normally wouldn't dream of questioning. Becker, 23-year TV veteran, says the HUT level drop won't worry him unless it is also reflected in the city-by-city ratings "sweeps" for the month of November. These results are not yet in.

And if the viewer decline is confirmed, will the networks make less money? "I believe not," Becker says. "Pricing in television is like an auction, supply and demand. The thing people don't realize is that for a mass advertising medium, TV is so inexpensive! You may hear of a one-minute commercial costing $100,000 or whatever, but what that means is it's costing an advertiser, say, [Word Illegible]7 of one penny to reach a household.

"So it becomes .72 of a penny - so what? Our prices will stay the same. Only the effective cost to the advertiser will go up, and by very little."

We have to remember that networks and stations do not really sell advertisers time. They sell advertisers us - our eyes and ears and fickle attention spans - and they sell us in herds, in cost-per-thousand terms. The whole nature and slant of the medium is indeed mass. Maybe we'd like to think it would be just wonderful if the HUT level drop is true and people are tuning out from disgust at shoddy programming, but this is very, very, very unlikely.

"After all, it's been the same basic programs around for 25 years," says Mord philosophically.

"Those who think cable TV or any other development is going to harm the networks always assume that people don't like what they see on television and are longing for something else," Becker says. "Well, I don't think people hate what's on television.

"I think they LOVE what's on television."