There is something irredeemably patronizing about much of the wowed response to Rosalynn Carter's trip - "Would you just look at that little lady, standing right up there talking about arms control . . . I mean, did you ever?" Let's knock it off. The size of the female brain is not the issue. Nor are Mrs. Carter's own savvy and sense in doubt. To me, anyway, the question raised by her Latin American trip is not whether Rosalynn Carter is capable of serving as an agent of her husband's government, but rather whether she should. That's the hard one - the question lurking beneath all those layers of pink whipped-cream prose in which we traditionally discuss the role of a President's wife.

Mrs. Carter has told us she means business. I see no reason to doubt her. Like the cliche of a substantive vice presidency, so the cliche of an activist, engaged "First Lady" seems unexpectedly to be coming to life in the Carter administration. That may strike you as little more than an inevitable consequence of the women's movement, heightened consciousness and the rest. But the first thing to understand is that women's-movement issues are only peripheral to the subject at hand. For Rosalynn Carter's self-professed role is not only different from that prescribed by the sisterhood for political wives, but also, in some respects, antithetical to it.

I have in mind the much-vaunted feminist goal of wifely independence, the newly argued entitlement of a political wife to a separate set of views and purposes and a First Amendment right to air them - never mind that they may cost the old boy his job. Martha Mitchell was the extreme case, Betty Ford a far less tumultuous example. Both were admired for their outspokenness, for their insistence on maintaining an identity an identity that was sometimes at cross-purposes with their husbands' political needs.

Well, no wire-service reporters are going to stay up late waiting for indiscreet phone calls from Rosalynn Carter - or even for heartfelt, more-in-sorrow disagreements with presidential policy. She doesn't see herself that way or fancy the role: Again and again she has publicly defined herself as a political wife. To be sure, she does not busy herself with the relentless trivia of Washington-wife culture, that gardenia-reeking world of party favors and ladies' lunches, which is, in any event, rapidly going out of fashion. On the contrary, she has an affinity for serious, substantive things that matter; Mrs. Carter sits in on important meetings and involves herself in some of the most consequential decisions her husband has to take. But she evidently sees her ticket to the world of policy and her special value in helping to formulate and promote it strictly as a function of her relationship to Carter - of her being, as she has put it, "the person closest to the President of the United States."

What we have here, in other words, is not an "uppity woman" issue, but rather a question of the proper role in government of unelected kin of elected officials. How accountable are they for whatever influence they exert? What do we owe them in the way of license to practice? These preplexities are as old as the public, and people are still plenty skittish about them. In fact, we sometimes seem downright manic on the subject, swinging from highs of adulation for a President's family to lows of suspicion and mistrust. In one breath we will announce that is a vile invasion of privacy and a show of grossest disrespect to dwell on the personal lives of the President's family; in the next we eill worry that they are beginning to act like royalty, that they are exploiting the taxpayers, that they constitute, somehow, a sinister force.

This crazy swing of attitudes has been particularly intense where a politically active wife is concernced. One the downswings, she is variously regarded as the seductress, the bewitcher, the mysterious power behind the throne, the possessor of unfair advantage and the wielder of undue influence. This "monster" image, as a Carter aide described it, is a peril of which the White House is aware. And people who work around the Carters know that it can be bestowed without justification on a wife who is only trying to help. But that, evidently, is cause only for caution, not for a back-to-the-drawing-board look at Mrs. Carter's role. The President reportedly wants Mrs. Carter involved in the business of state. She was involved in his governorshop of Georgia and he liked it. He also regards family as uniquely suitable emissaries for certain purposes: Their presence on a given scene, he feels, is an earnest of his own personal interest in the matter.

All this is in keeping with Carter's predilection for using out-of-channels, bureaucratically unencumbered agents and spokesmen to conduct his business. But it is also part of an understandable and time-honored tendency of Presidents to find concerned, energetic family members the most desirable of all officials "staff." Close and knowledgeable kin can be trusted absolutely to have a President's interests at heart; they have no separate ambition to fulfill; and yet they can also talk back and be frank in a way that's just not available to the hired help. Robert Kennedy in the aftermath of the Bay of Pigs, Julie Eisenhower as the walls of her father's administration came tumbling down - there are clearly times and circumstances when only family members will do.

Still, I think Carter intends to make much more governmental use of his wife than has been done in the past, that once again he is going to break out of the conventional presidential mold - and that, unless he and his wife are very sensitive and very astute about it, the prospect has trouble written all over it. If Mrs. Carter is going to conduct diplomatic discussions abroad and enter into policy matters in a systematic way at home, her efforts and her influence are going have to be judged as those of an ordinary professional. There is going to have to be a normal accounting - and a normal willingness to accept unsentimental scrutiny. Traditionally, presidential family, especially wives, have enjoyed a kind of protected status akin to diplomatic immunity. They also communicate with their husbands under a categorical grant of executive privilege. And it is generally regarded as loutish to write about or discuss them except with that trusty old pastry bag and the endless supply of whipped cream.

Mrs. Carter, by her very seriousness of purpose, is inviting an end to this facade of deference. She is asking to be part of the political and governing process, and the answer to whether or not she should do that is this: only if she agress to make herself accountable in the ordinary way. I calculate that before it's over, Mrs. Carter - a remarkable woman - will have demonstrated whether or not a political wife who comes out of the kitchen can stand the heat.