I have been trying to figure out what it is that is so peculiar about the preconvention struggle now going on to stop Jimmy Carter's nomination. Presidents have been in low estate in the polls before. Last-minute jitters, made worse by new bursts of scandal a la the Billy Carter affair, are par for the course. And so are the attempts of rivals for the nomination to cast as matters of conscience, fair play and even the survival of the Constitution, procedural changes they wish to make to their own advantage. You may take it as an ironclad rule that all the passions evinced on either side of these explosive, eleventh-hour procedural conflicts or either overwrought or phony.

Did I say "passions"? It's an odd word to use in connection with Jimmy Carter. You sense that the minute you've said it, there, it seems to me, is the first clue as to what's wrong. As I write, they are betting that not even the combination of Billy Carter, Teddy Kennedy and Edward Bennett Williams will be enough to bring Carter down. But, whichever way the conflict ends, it strikes me that the most distinctive thing about Carter's defense is not its toughness, but the fact that it apparently engages so little beyond itself in the way of feeling or loyalty to program or constituent fervor. He will win, they say. He has the votes That is that.

Four years ago, courtesy of Robert Strauss' genuis and obsession with party unity, the tableau behind a newly nominated Jimmy Carter was almost a sight gag. Just about the only reason for not being on that crammed platform, if you were a Democrat of national note, was that you were dead. Strauss would accept no other excuse.So, there they all were, waving, at one: George Wallace and Barbara Jordan and Scoop Jackson and George McGovern and Hubert and . . . and . . . and. Only now one sees that this was an illusion. Yes, the party wasn't at its own collective throat, the way it had been over the years. But Jimmy Carter, while perhaps a "unifier," was not an embodiment or even an agent of the various institutional and political interests these leaders represented. And three and one-half years into his presidency, he still is not. It is a one-case-at-a-time, personalized, loner's presidency. And this, it seems to me, accounts for the relatively noiseless and joyless way its defenders are defending it.

I am aware that noise and joy and sweaty high emotions in general can often be the expressions of all that is worst in politics. People never cheer so loudly nor support so blindly as when they are embarked on some vindictive crusade against their fellow citizens or when they are defending obsolete policies with which they are identified and which have failed. In the camps of Carter's various antagonists from Reagan to Kennedy it is surely true that some of this, in fact a lot, prevails. Still, I think it must be accounted a failure of Carter's that he has been able to generate so little feeling of his own and so little collective sense that he represents an identifiable program -- certain values and choices and priorities -- that an identifiable group of voters thinks is right.

It is more than a desire to put some distance between themselves and Carter's foul-ups that has bred this curious detachment of the president from his constituents and supporters. It is, in addition, Jimmy Carter's own brainy, analytical and, in a sense, apolitical way of espousing positions. His policies do not hang together in any familiar, warts-and-all way.They do not represent a political bent or prejudice or predisposition. They often are politically contradictory. So they do not attract or bind a single kind of voter. Within any of the countless groupings of voters that exist, the individual must choose between Carter actions that attract and repel.

And he is no more all-out in his approach to the leaders of other institutions -- Congress, trade unions and so forth. It was an ill-considered boast of the president in 1976 and generally into the first year of his term that he had won the nomination and the office by himself -- on his own, without help, without occuring debt or obligation. Both he and Mrs. Carter frequently made this observation, and it always had a ping different from the one intended. You didn't think so much of Carter as the independent rescuer of politics from the cronyish arrangements that had plagued it. You thought of him as isolated, wary, stingy, even "conceited," as we used to say in high school -- unwilling to share the glory of the achievement or to depersonalize the office. It was the Carter Presidency, not the Democratic Presidency. The trouble was that he was owed as little by others as he himself owed them. And I don't think that in four years Carter has changed that at all. He is as distant now and disconnected from, say, the leaders of Congress, the union types et al. as he was in the beginning.

Party, program and even the office of the presidency itself have been made to yield to this curious insistence on an independent, nontraditional and uninstitutionalized role. The plan for resolving the Billy business, at the moment I write, is for the president to appear before a congressional committee to testify and be examined. I think it is a terrible idea, and not just from the separation-of-powers point of view. Politically, getting into the witness chair is to assume the suspect's role. It is demeaning for a president. Carter takes not just himself, but the office there. And yet, he has said he would do it. This is a virtuoso performance we have been promised, not a presidential one. It is the moral equivalent of jogging -- lonely, a personal endurance test, not something that has to do with the general well-being of the group as a whole.

Maybe this curious Carter presidency is right for the transition from old to new programs and alignments the country is experiencing. It is such a mixed bag and elicits such mixed emotions. It has been, like the president, at once poignant, desolate, well-meaning, self-righteous, unemotional, rational and better able to demonstrate that the opposition was wrong than that it was right. It is a one-man show. No wonder the presient's side, though convinced that he is better than the competition, doesn't seem to be in full voice.