Jimmy Carter is going to hold a White House conference on the family next year, and HEW Secretary Joseph Califano will certainly bring in large numbers of psychologists and sociologists to tell us what's gone wrong.

I mean, the divorce rate is almost unbelievable - higher than any other country in the world. We've come to the point where the marriage decision is like the decision on what movie to go to on a Saturday night. If we don't like it, we can always walk out. Troublesome, but no disaster.

And I'm sure it will be pointed out that this new fact of American life is helping to produce all sorts of other facts even uglier to contemplate, such as an extraordinarily high rate of serious juvenile crime, not merely dangerous ranks but robbery, arson and murder.

Maybe the national decline in student test scores is a result of the large number of children living in one-parent families, which in turn is a result of the divorce rate.

I think the White House conference is probably a good idea, for it may focus our attention on this seamy and vexing side of our national life. Yet I can predict with certainty the kind of thing would help, But I am not sanguine. I think the problem is much more personal, involving rules of conduct and faith that we have forgotten or not applied.

An example is Rule One, about which I was reminded just the other evening.

My youngest son had gone to a wedding and managed a seat right up in a front row. At dinner later, he turned to my youngest daughter and asked: "What is troth?"

He explained that both the man and the woman had used the word in the ceremony he had witnessed and that it was "sort of a funny word."

Which it is, if "funny" can be defined as archaic. But in any event, Elizabeth replied that it was hard to define "troth," but that she knew it was "a good thing."

At this point, the older children began to laugh at Elizabeth for pretending to know more than she did, so I entered the discussion, explaining that "troth" is an old-fashioned word for "promise" and, while I was explaining, an unusual thing happened.

A lot of years and scenes passed before my mind. I saw a lot of different kinds of wallpaper in a lot of different bedrooms. I saw houses I had almost forgotten. I remembered children born, times we were hurt - and if one of us was, the other always was, too - and times we were gay, times we were broke and times we thought we weren't, times of pride and grief, and even shame.

I thought of quarrels and of making up again and of how one person can often make another "come off it." But I also thought of times when I had not "come off it" and been angry and even mean. I thought of the first dishes we ever bought and how there is one left. I saw it the other day in the cupboard with a big chip, and maybe, I thought to myself, that's what troth is - the last dish.

Anyhow it occurred to me - and I explained it to my youngest son - that marriage is based on nothing more than a promise, a promise between two people, and that therefore the word "troth" is not to be taken lightly but is possibly the strongest word in the English language.

So that's Rule One, for which I am indebted to Elizabeth, and I told the other children that Elizabeth was not to be laughed at, because she was absolutely right. "Troth is a good thing."

I'll bet there's not a single mention of Rule One at the White House conference.