For this reporter, the last weekend of the longest campaign meant a final flight down the East Coast and a return home to Washington. I confess to being a romantic about that particular route: no matter how many times I've made it, nor how fatiguing the journey about to be completed, when the plane banks low over the Potomac and heads down river over the capital city I still feel an almost indescribable lift. Perhaps that's naive, but on this especially golden fall day the contrasts between the beauty of the national symbols of governance below and the feelings about Washington, the city of politicians and power, held by so many citizens around the country seem especially vivid -- and saddening.

But no more so than this campaign.

In other presidential campaign years, after similar long trips around the country talking to voters, I always came home with a strong sense -- a conviction, really -- of who would be the winner. You knew, even if you didn't want to say so in print. That is not the case today. Never has there been so much anguish over how to vote, and for reasons all Americans understand.

In a stack of mail on my desk I found two letters, among many on the same subject, that express a common dilemma and question. The first is from Marguerite Morris of Narberth, Pa. She writes, in part:

"Frankly I, like many of my fellow Americans, am agonizing over the choice of Reagan or Carter for president. It's very puzzling, as the parties seem to have switched stands. Here's Reagan extolling the virtues of Franklin Roosevelt and railing against Carter's economic policies, and Carter hinting that, if elected, Ronald will get us into war.

"Do you think Mr. Reagan is as uninformed as he sometimes seems to be? Do you think the California clique which was behind Richard Nixon is also supporting him? Do you think he will name able men or will it be the archconservatives to whom he must be indebted to some degree?

"Do you think President Carter may improve with time and provide the leadership criminating interview on the Donahue show last year with [Chicago] Mayor [Jane] Byrne, and she did everything but call the president a nincompoop. She seemed an intelligent, astute lady, but then again maybe the president had denied her some favor.

"It's very difficult to know whom to believe and, in that regard, I don't always trust the media either. To make matters more agonizing for me, my youngest daughter will cast her first vote. Some choice, isn't it? She is looking to me for guidance, and I am looking to you for some clues."

Mrs. Morris, I'm flattered that you think I could help resolve those questions, but I feel inadequate to do so. Yours are the very questions I have been asking myself. I know many others share our quandary. Three questions you pose are critical to the outcome Tuesday: whether we could expect a better performance from Carter in a second term, whether Reagan is truly informed on the great range of issues he would face in the White House, and whether he would surround himself with outstanding people. I find it almost impossible to asses a second Carter administration; I believe Reagan to be woefully uninformed on many issues, and I think he would bring competent, if not outstanding, people to Washington. But these are only guesses. It is a sorry commentary on the quality of this campaign that the candidates have failed to give us adequate information on which to form those vital judgements. We are left with impressions. They are, of necessity, superficial. But they will have to do. Obviously, how a person finally answers these questions will determine who occupies the White House.

My strong suspicion now is that most voters have come to terms with their anguishing inner dilemmas.

In the last few weeks it has been been clear, to me at least, that there is a move toward Reagan. The doubts about him -- his misstatements, his possible recklessness, his real abilities -- have not been entirely dissipated, but many people I've met in this period seem to have had new thoughts about Reagan. They have become either more reconciled to the idea of a Reagan presidency or more reassured by him. I think last Tuesday night's debate, in particular, was helpful to Reagan in that regard. If he really is getting more of those undecided voters because of his Tuesday performance. Reagan's already powerful position has been strengthened immeasurably. He began this campaign with a commanding base of western and southwestern strength in the Electoral College; he does not appear to have been diminished there at all.

That brings you back to Carter. The electoral map has not favored his prospects all year. In fact, in the cold arithemtic of American politics, as dictated by the solid bloc of more numerous -- if not by any means all more populous -- states that have been aligned with Republican presidential candidates in recent elections, you could make a convincing case that Carter never really had a chance this year. And that would be making the same mistake that pollsters and political analysts have made consistently about Carter all along, and not just this year but from the time when he first implausibly entered the presidential race five years ago.

Therein lies the remaining riddle of this election. It is one I believe no pollster will pick up, for it deals in the most illusory of intangibles.

From the beginning of his presidency, Jimmy Carter has carried with him more than the normal hopes Americans give every new chief executive. He came to office amid the wreckage of American political leadership scattered over nearly a generation -- the murders of the liberal Democratic Kennedy brothers, John and Robert; of the black leaders, Martin Luther King Jr. and Malcolm X; of the destruction and disgrace of the Republican conservatives, Richard M. Nixon and Spiro T. Agnew; of the failed presidency of Lyndon B. Johnson and the bullet that ended another career, George C. Wallace's. Out of such trauma came a hunger for a period of national stability. Today, in a time that appears even more threatening and uncertain, the public desire for presidential continuity remains strong; presidential experience and stability, no matter how difficult the incumbent's experience have been, are still powerful political factors in this election.

And, paradoxically, I think Carter also helped himself the other night when he struck that chord by referring continually to aknowledge only a president can calm -- making war-and-peace decisions alone in the Oval Office. His greatest source of strength comes from those who believe him to be most careful in exercising his responsibilities from experience painfully gained over the last difficult four years. All of which leads to the critical final puzzle, the one on which this election hangs -- the turnout Tuesday.

George Gallup and other experts have been saying the turnout this year may be the lowest since 1948. If that's true, it certanly works to Reagan's advantage, for Carter will have failed to rally the traditional Democratic constituencies for one last presidential roll call. Strangely, despite all the unhappiness and negativism of this campaign, my travels have led to a different impression. People I've kept meeting have been following this election intensely. They say they are planning to vote, that this is one election too important to sit out. Quite possibly my experience has been misleading, but I wonder if the turnout won't be greater than predicted. If so, it could be the sleeper in the election.

A clue of a kind, lay among the letters on my desk. Mildred Holcomb, of St. Peter, Minn., my correspondent from afar whose views have appeared in this corner from time to time, had written twice. A month ago she spelled out her anguish over her presidential choice, but concluded then: "I think I will gamble on Jimmy again, as there is no hereo to give our asoration to. Heroes are out of date in our time." Last week's letter told a different story:

"Voting will be a debacle as far as we are concerned," she wrote. "We have voted in every election for over 50 years, and this year we are going to sit it out at home. My husband can't see to mark the ballot, and I feel it is too much trouble to call for a ride. I know it is the coward's way out, but I will have six grandchildren voting his year, and I do not want to null even one of their votes, as they are voting for the world that they will live in. I am tired of old people going to vote just for themselves . . . ."

Tuesday will tell the tale of whether she's the exception or the rule.