SARAH WEDDINGTON, the Texas attorney and Agriculture Department general counsel, who has been appointed to a special assistant's job at the White House, was reported to have said the other day that she intended to be involved in more than women's issues. We think that's a good thing. But it doesn't change our view that the job should not exist in the first place. Mrs. Weddington has evidently been retained to serve as a kind of ambassador to and from Women. There has already been an ambassador appointed to and from Blacks and also one to and from Jews. Yes, we know that's a rather crude way of describing these appointments, but there are times when a little crudity may tell you a lot more truth than your average delicate official announcement.

Evidently the decision to create the post Mrs. Weddinngton will hold owes something to the last funfilled days of Midge Costanza, the theory being that women would somehow take it amiss if they didn't keep one of their own right there in the White House committed to the furtherance of women's interests and concerns. After Anne Wexler, Miss Costanza's original replacement, had enlarged the scope and sharpened the purpose of the job, recreating it as, politically speaking, a unisex office, concerned with getting the president's general program through, it was felt that the women's-issues part of the job needed to be reconstituted. And that is how Mrs. Weddington came to be appointed.

You don't have to believe that the larger public-policy questions she will be concerned with are unimportant (they are not) or that the Carter White House is the first to have organized itself along the lines of a campaign headquarters (it is not) to believe that these ethnic and other special-interest-group presidential appointments are a rotten idea - they are. Largely for emblematic reasons, practically everyone these days seems to want either a Cabinet department or a "special White House assistant for . . . " or both. But an assistant for black or Jewish or women's affairs makes no more sense and is - when you get right down to it - no less inimical to the interest of the groups supposedly being favored, than is, say, the idea of a Department of Peace. The process does not expand, but rather diminishes, the reach of those who would do something about the issues in question. Peace, social equity, racial justice and the rest should be made to be primary concerns of all government workers, agencies and policies - not compartmentalized and thereby converted into special, parochial "constituent" concerns that may be safely left to the proper bureaucratice organization.

Finally, we note a flaw so fundamental and conspicuous that it often escapes notice: Not all women (for which you may also read Jews, blacks, etc.) see the public-policy issues concerning them the same way. The many women who oppose the Equal Rights Amendment, which we happen to favor, are also - are they not? - women. And so, surely, are the many Catholic and other women who are deeply opposed to Mrs. Weddington's strong stand in favor of a woman's right to choose abortion. We note, in this connection, that Mrs. Weddington's appointment has been severely criticized by the general secretary of the U.S. Catholic Conference. One answer to this, we suppose, would be to appoint - what else? - a special White House assistant for Catholic affairs. But where, finally, would be process end?

We'll tell you where we hope it ends: with a withering away of these special-interest assistantships as the Carter administration wears on the gets more self-confidence, if it does. The misguided pressure for these appointments from various lobbying groups tends to be intense. But it would be nice if, at some point, Mr. Carter turned thumbs down. Somewhere in this land of ours there should be a place, an arena, a jurisdiction, where the better aims and interests of all Americans are taken into account, adjudicated when in conflict, and furthered by means of governmental action. Not to be coy about it, that's what we thought the presidency was all about.