The telephone always waits to ring until you're in the shower. The county chairman, a philosophical sort, knows that well enough, so he wasn't terribly chagrined on New Year's morning when his first shower of the new decade was interrupted by the commanding jangle of the phone.

And the chairman wasn't terribly surprised when he picked up the receiver and found himself, stark naked and dripping wet, in the middle of an amiable conversation with the president of the United States. The chairman (who has requested anonymity) knew well enough that Jimmy Carter was calling all the Democratic county chairmen in Iowa, and sometime or other it was bound to be his turn.

"Actually, we didn't say much," the chairman recalled later. "The president said 'Happy New Year,' you know, and he said he'd like to have my support, but he didn't really go into any issues or any campaigning.

"Mainly, he said he wanted me to watch the TV ad he had put out about the White House, and he said that would sort of say what was important about the election and what he has been doing."

Having heard the president himslef reduced to touting a TV ad, the chairman wasn't terribly surprised a few days later when Ted Kennedy came barnstorming through eastern Iowa and gave a speech to a big audience in the chairman's town. "First of all," Kennedy said first of all, "we want to ask you all to remember to tune in our TV program next Monday night at 6:30. That will tell why it is that we're running for president and what some of the important issues are."

Historians, start your typewriters. Sociologists, man your computers. What we have here are symptoms of a major epidemic that has swept over American politics in the past few years and is not so prevalent that even the politicians have stopped lying about it: the total subjugation of political man (and woman) to the media.

It used to be that media advertising was seen in the political industry as a means to advertise the candidate. Today, the roles are reversed: The real-life candidate is a shill whose job is to advertise the electronic image that bears his name.

This development is not limited to democrats, nor is it solely the preserve of presidential campaigns. All sorts of candidates in all sorts of elections nationwide have become more and more willing to admit -- or, perhaps, less and less able to hide -- that what happens in their advertising has more impact on voters than what they do in real life.

Last fall, to take one of countless possible examples, I went to Boston to cover the campaign of Mayor Kevin White, the nation's senior big-city mayor, who was running (successfully, as it turned out) for a fourth four-year term at City Hall.

White told me, as he told everyone else, that he was sure he would win. Why? He didn't mention his stand on taxes, his record on crime, his achievements in public transit. The first thing he said was "You've got to see my ads. They are powerful."

The phrase sticks in the memory not because it was unusual but rather because it was almost identical to other boasts from other candidates in other states. Riffling more or less at random through a stack of notebooks, I find virtually the same comment from Michigan gubernatorial candidate William Fitzgerald ("The first thing you've got to see is these ads I'm hitting him with"), Arkansas senate candidate Ray Thornton ("We've got some television spots that are really going to do it for us"), Wyoming congressional candidate Bill Bagely ("We've got this jingle we're putting on every station in the state").

It is unfair, perhaps, to single out these worthies, because they are no different from other modern-day candidates in realizing a basic truth: Nobody is as good in the flesh as he is on tape.

Consider the real-life human candidate going about his activities in the actual world. He is bound to make some mistakes, say some syntax. But the same candidate, preserved on magnetic tape in the sanctity of his advertising agency, is a superhuman whose only shortcomings are those that have been programmed in to make him look like that paradigm of political virtue, "the regular guy."

If the advertising man's art often portrays a heavily retouched picture of life, on some occasions life begins to imitate the art. The example that springs to mind is Gene Stunkel, an amiable, easygoing, garrulous small-town businessman in downstate Illinois who ran for Congress in 1978. Stunkel's ad man made six spots depicting the wealthy candidate as s tough, no-nonsense decision-maker who was absorbed in the problems of the working man. Stunkel bought a Betamax and carried it in his car so that he could watch the sports in his hotel room each night on the campaign trail. And gradually, the candidate in real life began to talk and act like the person depicted in the ads: the man turned into his own image.

So who can blame Jimmy Carter for asking county chairmen to judge his televised performance rather than the real thing?According to reports of some of those who worked for him, Carter in the White House has been a simpering, indecisive lightweight who could not discipline his staff and who was so inept at delegating authority that he even maintained personal control over the hourly schedule on the White House tennis courts.

This Jimmy Carter bears almost no relation to the president of the same name who appears in the half-hour TV commercial that Carter asked our county chairman to watch during that unfortunately timed telephone call on New Year's Day. The Jimmy Carter of that particular stretch of videotape is a tough, agressive leader who depends on a passel of highly competent aides and who spends his time worrying not about tennis schedules but about tensions in the contentious modern world.

The same magic transformation has taken place for Kennedy, who suddenly starts talking in complete, coherent sentences when he shows up in a commercial, for Howard Baker, a diminutive, casual guy who turns into a fire-breathing giant in the TV ad that media types say is the "most admired" of the 1980 campaign, and for just about every other candidate who has taken his human frailties to Madison Avenue to have them disguised.

The only humans left are the voters, sitting forlornly in front of the tube and trying to decide which of these fleeting electronic images might turn out to be best at governing a country of real people.