No subject lends itself more readily to melodrama and romance than presidential "decision-making" - the Awesome Burden, the Loneliness of Command and the rest of that media junk. So it is with a certain uneasiness that I record the following thought, even though I believe it to be true: In the past couple of weeks, Jimmy Carter has made some decisions that are distinctively presidential in nature and which will almost certainly mark a turning point in his presidency.

I am referring to the collection of choices and moves that add up to the Carter anti-inflation and dollar-rescue program. With due respect to all those people who got elected and defeated last week, I think this - the apparent change in Carter and the impact his policies will have on his own party, not just the economy - is the political fact of the season.

Carter's performance can best be defined by what it is not - presidents, after all, are always seeming to make momentous, or at least consequential, decisions, and that is part of the problem in spotting a real one. My own negotiative checklist against which to measure for authenticity begins with this simple question: Has anything actually been decided? Generally, the answer is no. And often as not that is because the decision was never the president's to make.

I give you, as an example, the great groaning genesis of the Carter energy policy last year. Lights burned late, important cars pulled in and out of important driveways, government people went around looking harassed - all the requisite imagery.And so we wrote about Carter's big energy-program decision - which was fine except that it wasn't a decision. It was an anouncement. Carter announced what he wanted a lot of other people to decide. The important decisions weren't his, as we (and he) were all to find out in time.

You would not have judged this to be the case from the atmospherics at the time, and that is part of the problem too. I sometimes think that the worst and most deforming thing that ever happened to the political press in this country was the Cuban missile crisis. We tend to force everything presidential into that particular mold, tracking in infinite detail who said what at which meeting, who switched sides, who took a middle position and who finally prevailed in the struggle for the president's mind. What regularly gets left out of the narrative is the question of whether any real choices were made.

Carter, until now, has been as good as any of our presidents and other political leaders at making lists instead of making choices, at refusing to pay in something or yield up something for the sake of getting something else. The contemporary prototype of this mode of behavior was Lyndon Johnson's refusal to choose in relation to the Vietnam war, his belief that he could have the war and the Great society at the same time without facing up to the monstrous tax burden this implied. Carter in his two years has not begun to do anything so cataclysmic or disastrous. But he has, on fiscal and monetary questions, refused to choose. He has gone from one emphasis to another, declining to move in a way that would close off any options and insisting, for the record, that we could, somehow, have it all.

That is what has changed, especially with the dollar-rescue effort that Carter announced when his anti-inflation phase-two program met with domestic and international contempt. The president identified himsel with one side of the argument. He took action that was his to take and made things happen that had consequences. In doing so he gave up some alternatives and some illusions and some support. Practically everyone agrees that before any longterm stable good can come out of the Carter policies and actions, short-term anguish of a kind that is especially unacceptable to Democrats - tight money, recession, unemployment - will have to be endured. Carter made that choice.

Around Washington there are still plenty of people who discount the boldness of the president's moves and who are skeptical about his saying power of the course he appears to have chosen. On the first of these counts, it is regularly pointed out that the calamitous response of the money markets to Carter's phase-two program left him no choice but to respond as he did on the dollar, the conclusion being that Carter didn't "choose" in any real sense at all. There is something to this. But it is also true that the president had been resisting for months the importunings of the financial community to move in to defend the dollar, and what two of his advisers described to me as the option of "hunkering down" was at least believed to be available to Carter even as the great dollar crash was occurring. Yes, there was intense pressure, an almos irresistible pressure - but a temporizing president could have devised a way around the tough and hard-to-reverse measures that he did take.

The other half of the skepticism goes to the question of persistence and commitment. How tough will Carter be on the budget decisions that are being made now? How durable is his devotion to defense of the dollar?Those who view the administration's actions as little more than a frantic last-minute emergency effort, a kind of time-buying maneuver, insist that when the worst heat is off, the administration will revert to its ambiguous, have-it-all ways.

I get a sense that the commitment is real and that you will be able to measure it from the hollers that are going to go up from the basic political constituency of the Carter White House before it is over the minorities, the unions, the city-dwellers. One of the thinkgs that was kicked back and forth a lot in the meetings that preceded the phase-two unveilling was whether or not to put a hard figure on the target budget deficit for next year. The decisions to do so - the proposed figure is "below $30 billion" - was evidently intended by Carter to fix his policies in concrete, to make it much harder, if not politically impossible, to whirl around and start off in some other direction.

To me, anyway, all this has the look of something that really happened - as distinct from that mirror-and-shadow play that so often passes for high politics in Washington. The president looks as if he has made some truly tough and - yes - presidential decisions. He has decided he can't have it all. He has agreed to give up something - in fact, plenty - to get what he thinks he can and must achieve. He has taken some king-size risks, with his own political reputation among other things. He has started some processes in train that he really can't call off - or at least not without a political plunge that would make his doldrums of the summer look mild. Maybe the importance of a presidential decision is in inverse proportion to the amount of sound and fury that heralds it. This time there wasn't much noise, and this time I think Carter has really done something.