As an offshoot of the Carter papers case, we are hearing a new version of the old line, "Everybody does it." This time, it is being said of journalists in our sometime role as campaign advisers.

Columnist and television commentator George F. Will has acknowledged seeing some of the papers copied from President Carter's files on the kitchen table of David A. Stockman, before they helped prep Ronald Reagan for his 1980 debate with Carter. Will's role on the Carter debate team had been publicized at the time, but when it came up again, in the context of the possibly purloined papers, it stirred fresh debate.

My intention was to keep my mouth shut. Will is a good friend. I regard him as the best hope for genuine intellectual distinction that journalism has produced since Walter Lippmann. Besides, as you will soon see demonstrated, it is difficult to write about "journalistic ethics" without sounding like a jerk. I am the keeper of no one's conscience but my own--and that is constantly in need of repair.

But I cannot accept--or let my silence seem to lend assent to--what has become the widespread assertion that "everybody does it." There is too much danger in that myth taking hold.

When viewers turn on television commentary these days, the journalists they see are often straight out of the political world--often from previous White House staffs. One election's losers now easily become the next election's pundits.

But it is not just these gypsies who suggest that the line of distinction between politicians and journalists is fuzzy, if not invisible. My friend and colleague of 23 years, columnist Mary McGrory, has written, "Scratch a scribe in this town and you find a campaign manager."

The Washington Post's deputy managing editor, Richard Harwood, a hard- nosed political writer if there ever was one, has confessed that he was the "ghost writer" of speeches he covered years ago in a Tennessee legislative campaign. He has cited a long list of other journalists, living and dead, who privately have helped those in power or seeking power to gain their ends.

The message the public must take from all this is that "everybody does it." It's not true. More than 20 years on the press bus have shown me fewer journalists peddling advice to politicians than there are writing advice to the lovelorn. And with just about as much impact.

When I was a pup on my first presidential campaign, I was given the best advice I ever received from the best political reporter and columnist I know, Alan L. Otten of the Wall Street Journal. Otten observed that several of our press colleagues had been seduced by the charm of John F. Kennedy into thinking themselves assistant campaign managers and, as always happens in such cases, had made themselves ridiculous in the process.

But he said that in the roller coaster of intense emotions of politics and government, it is very easy for reporters to think of it as "our campaign" or "our administration." Easy--and fatal.

Otten said there was only one way to remain reasonably straight: "Always set yourself to lean a bit against the people you're covering, and hope whoever is covering the opposition for your paper does the same thing."

The need to fight off the impulse to camaraderie--to maintain an adversarial posture, if you will--is one thing that precludes the intimacy of an adviser's role. But there is a more important reason.

I think most political journalists--reporters or commentators--feel we occupy one of the nation's favored positions. We have access to the minds of many of our fellow citizens, uninhibited by any serious censorship. That is a rare privilege. It is also a form of power. And like any power, it can be exercised justly only with an awareness of the responsibilities and inhibitions that go with it.

As journalists, our responsibility is to the reader. Anything we learn, or think, belongs first to that reader. Not to a politician who happens to be a friend.

As journalists, we owe that reader the fullest and fairest rendition of the facts we can provide, and the clearest judgment we can muster, unimpeded by the wish to see some privately recommended strategy fulfilled. That obligation does not change if we call ourselves reporters or commentators.

For the privilege of being political journalists, we accept certain inhibitions. One of them is forsaking the role of political activists--or strategists. It may not be unethical to do both. But it is surely greedy. And that kind of greed properly invites the distrust of the reader who must wonder where our first loyalty lies.

These are the considerations that make it easy for most political journalists to demur when a politician asks the flattering question, "What do you think I should do?"

The answer is simple. "You want to know what I think? Buy the paper. It only costs a quarter. You get all the ball scores and comics--and they toss in my advice for nothing. Which is probably what it's worth."