IT IS AMONG the ending misfortunes of this campaign that in the one area where you would most hope for a stark and useful difference between the candidates -- their approach to and skill at using presidential power -- none exists. They are different, but not in a very helpful way. Jimmy Carter has been notoriously uneven in this regard. His better intentions have frequently been confounded by a lack of political imagination, empathy and will. And sometimes they have succumbed to a streak of pettiness. The president's recurrent failures to use the powers of his office well have often amounted to abdications of responsibility. The troubling question is this: what evidence is there that Ronald Reagon has a better idea?

It is conceivable that Mr. Reagan in office could surprise the world with a gasp of the important (and selective) uses to which the presidency can and should be put -- and the attendant difficulties of doing so. But surprise is the key word. Not even his partisans' most glowing renditions of Gov. Reagan's time in Sacramento provide any notable support for such an idea. Mr. Reagan, it is offered by these fans, was reasonable, open-minded, pragmatic, unvindictive and willing to put good people in important jobs.

But none of this speaks to the point. In terms of managerial "reform" presidential candidates inevitably make -- Mr. Reagan tends to repeat many of Jimmy Carter's four-year-old fatuities: cabinet government, decontralization of White House power and so forth. Beyond that, there is the unhappy fact that very little Mr. Reagan has said indicates an appreciation of the fact that simply telling the federal bureaucracy what to do or instructing this one or that in the president's objectives isn't going to do the job. Skillful conduct of the office, otherwise known as "leadership," requires much more than that in the way of cunning, generosity, intuition, obduracy and a feel for the web of interests, egos and possibilities that is Washington.

Let it be said that at the end of 3 1/2 years, Mr. Carter has shed some of the harmful notions he brought with him to the White House on the subject of the presidency. By last summer he had recognized the merit (at last) of providing himself with a White House chief of staff. His let-a-hundred-flowers-bloom "cabinet government" ended with the kicking out of several cabinet members who evidently took him to seriously on the subject. And he stopped cultivating certain images that people were coming to view as evidence of a passive, non-leading, not-up-to-the-job character. In short, the president has seen the need to seize control of his own government, and that is a plus -- though in the matter of politically exploiting some of the more sensitive cabinet positions for his own personal campaign purposes he has gone way too far.

This last point reaches the other element in the conduct-of-the-office question: the matter of personal characteristics. It is increasingly said in Mr. Carter's behalf these days that it is the issues -issues, not the personality-quirk issues that matter what's a little human frailty among friends? It is probably true that those of us who have had a couple of things to say about the nature of the president's campaign could do with a reminder that we are not talking about Caligula. But neither are we talking about mere minor idiosyncracies, as some now insist, that have nothing whatever to do with capital letter Issues. If the nuclear-trigger issue is as important as Mr. Carter says it is, then surely the personality and temperament, the decency of the conduct of the candidates under pressure, must also be an issue. And this is true across the (non-nuclear) board. For example, when Jimmy Carter retreats from taking responsibility -- as he did -- for the forced resignation of U.N. Ambassador Andrew Young, preferring instead to let the domestically hurtful and explosive notion get around among blacks that Jewish pressure did it, well, that is not an irrelevancy, a matter of only marginal concern to the way the man governs. Nor is the particular introversion and insensitivity that has often led the Carter White House to deal harshly with its potential friends in Congress or to project confusion rather than the authority of the office overseas.

And so, on the personal temperament front, one turns to Ronald Reagan. It is a cruel, and somewhat ironic, fate. Mr. Reagan is perhaps the last Californian on earth the rest of us had in mind when all that California business about being "laid back" and "mellow" was piped into our vocabularies. But it is precisely the offhanded geniality of the man that has been so unnerving. For one thing, it suggests a candidate conceivably too complaisant and suggestible to seize and truly assert control over the far-flung federal empire any better than Jimmy Carter has done. For another, it sits oddly with some of the truly spectacular misjudgments on issues the governor has made over the years. Self-evidently, he is not a cruel or unfeeling man. But some of the positions with which he has let himself be identified are both. Why? Does it speak of something more serious than merely a governor's necessarily more limited perspective on questions that affect everyone in the country? Does it speak of a geniality and "laid-backness" not just of the spirit -- or of style -- but of the intellect? A habit of accepting too easily and inspecting with too little rigor ideas and nostrums whose surface plausibility glosses over some fundamental flaw? Where in any of this is the prospectively strong and sure president for whom people are looking?

The point is this. There are pluses and minuses on the subject-matter issues. And pluses and minuses on other key considerations as well. But there is no way, given the nature of the two prime contenders for the office, that this country is going to elect a president in November who is especially gifted in or suited to the conduct of the office. And that is that.