VERY SOON NOW, John Anderson is going to start sounding like Bobby Kennedy. It won't be his voice or his manner or anything like that. Instead, Anderson, like Kennedy before him, is going to have to start explaining over and over again how he is sorry for some of the things he did in the past and how he promises never to do them again in the future. By comparison, though, Kennedy had it easy. He hever proposed ending the separation of church and state.

Anderson, of course, did. He did it three times, the last time in 1965, each time introducing a proposed constitutional amendment that would have had the "nation devoutly recognize the authority and law of Jesus Christ, Saviour and Ruler of nations. . ." while at the same time, it should be pointed out, recognizing the rights of others to both disagree and practice other religions.

Anderson now takes it all back. He says the amendment was a mistake and characterizes it as misguided, but innocent -- the result of some preacher entreating him to get the country back on a more moral and Christian course. To Anderson, a religious man, the amendment seemed like a good idea at the time. It no longer does.

This is the sort of situation that sets off a debate without end. The basic question is how much does a person really change. With Bobby Kennedy, for instance, liberals were chary of him because he had once served at the knee of Joseph McCarthy. Kennedy had an explanation for that (he was young; his father insisted). And he maintained that he and McCarthy were as different as two men could be. Some believed him and some didn't, but when he ran for the Senate from New York, there were enough lingering suspicions for him to lose the votes of many liberals.

In a sense, his younger brother Edward, now involved in his own presidential campaign, is plagued by the same question. In Ted's case, the albatross is not early employment by someone like McCarthy. It is, instead, the cheating at Harvard, and, later, the accident at Chappaquiddick. People wonder if these are the mistakes or, instead, examples of a blemished character.

Back to Anderson. Like Robert Kennedy, he gives every evidence of being -- as Jack Newfield once said of Kennedy -- a politician in the state of becoming. He started his political life on the right and has since moved so much to the left his fellow GOP presidential candidates suggested to him that he was in the wrong party. It turned out that he could not have agreed more. He went out and more or less formed a party of his own.

Anderson, or Kennedy for that matter, is not the first American politician to reverse the normal aging process and become more liberal as he got older. Franklin D. Roosevelt comes to mind, but the phenomenon is fairly common in Washington. The town is full of congressmen and senators who come out of the heartland brimming with conservative fervor only to see it all dissipate in the fabled salons of Georgetown. Usually, they wind up losing to some conservative, two, four or six years later. Had Anderson not gone presidential, this probably would have happened to him.

But where Anderson is a case unto himself is that constitutional amendment of his. Under no circumstances could you call it a mistake of youth. He was 43 years old when the thing last got thrown into the hopper -- a lawyer, lawmaker, former diplomat, combat veteran, Phi Beta Kappa scholar and Harvard man.

But more than that, the proposed amendment was not something as simple or as routine as an illiberal vote on an issue -- something you could ascribe to either Anderson's early conservatism or some desire to vote his constituency. He didn't do that, for instance, in opposing school prayer.

It was something else -- something having nothing to do with politics, but with what could be called a mind-set, a way of looking at things -- a conviction that he had something called The Truth. It was not, mind you, a truth, or his truth, but The Truth and it left precious little room for your truth or my truth or anyone else's truth. In this sense, what is important is not what the amendment said (it could have declared America as atheistic republic) but the thinking behind it.

It is this thinking that is disturbing about Anderson -- this iron-like certainty. Some people call it preachiness or shrillness or a tendency to lecture. But call it what you want, it persists years after the "mistake" of the proposed amendment -- raising the question of not whether John Anderson has changed politically, but whether, fundamentally, he has changed a lot, a little or not at all.