The most striking aspect of this dreary presidential campaign so far involves people's attitudes about Jimmy Carter.After weeks of travel and interviews it's literally true that I have yet to meet a single person who is happy about voting for him.

That doesn't mean there are no Carter voters out here, nor that the dedicated Carter loyalists have disappeared. Many people will tell you the specific reasons why they are voting for Carter . . . or why they have switched, say, from John B. Anderson to the president . . . or why they still may end up voting for him after those last hours of soul-searching before casting their ballots. And it doesn't mean Carter can't win.

But the attiudes expressed add up to a dispiriting picture of the president. In one way or another the people I've met have all had reservations about another four years of Jimmy Carter in the White House.

A few weeks ago, despite the polls of the time showing him behind, it seemed as if Carter was on his way to victory. The damage Ronald Reagan had done himself in the early days of his campaign appeared to be permanent; many of those who had been planning to vote for him would tell you they no longer thought Reagan was up to the presidency. Those doubts still persist, but they have been countered by new ones about Carter.

The first problem came when he turned down the invitation to debate his rivals, Reagan and Anderson. People wanted to see them together. In this year, even more than in past elections, they felt a need to form new impressions of how well the candidates handled themselves and addressed the nation's future.

Carter's refusal seemed specious and political. While it may not have changed many voters' minds, even his supporters were disappointed. It had a more damaging aspect: arousing memories of his refusal to debate Sen. Edward M. Kennedy all year long.

By last spring, the so-called Rose Garden Strategy that had worked so well politically for Carter in the early months of the Iranian hostage crisis had begun to turn sour. Traveling then you heard cynical remarks about his hiding out in Washington. Jimmy Carter's Rose Garden was the subject of jokes and late-evening talk show barbs that made their way around the country through TV. That impression of his playing politics over the issue of debating his opponents was reinforced this fall.

The second, and more serious, problem has been over the way he has been campaigning recently. There's no doubt that the kinds of personal remarks he has been making against Reagan have hurt him; Carter has been seen as petty and vindictive. Instead of elevating the campaign, he has given it even more of a negative cast.

His advisers in Washington are reported to have persuaded him to change his approach and stick more to discussions of issues. They surely are correct. The question now is whether he can rekindle the sort of support he enjoyed earlier this year, and, paradoxically, which was his through much of his troubled presidency.

Jimmy Carter began his campaign with an underlying layer of sympathy from citizens. No matter how plagued he was by problems and bedeviled by mistakes, people tended to separate the difficulties of his presidency from his personal qualities. Carter, the president, was not about to become an instant candidate for a Hall of Fame bust, but Carter, the person, was respected as a decent, intelligent, hard-working man of integrity.

More important, from a political standpoint, he was given credit for doing the best he could with difficult, if not impossible, conditions. He was seen as cool, rational, fair, dispassionate. His recent campaign attacks have raised doubts about the validity of that view of him.

In an interview with Barbara Walters last week broadcast over Abc, Carter acknowledged that he has made mistakes, and promised "to do the best I can to refrain from any sort of personal relationship with Mr. Reagan as far as criticisms are concerned. . . ."

He explained his behavior by saying, "Some of the issues are just burning with fervor in my mind and in my heart and I have to sometimes speak extemporaneously and I have gotten carried away on a couple of occasions." He also said, correctly, of Reagan: ". . . He shares part of the blame that I have assumed that the tone of the campaign has departed from that which it ought to be between two candidates for the highest office of this land."

When people ask you who's going to win, as if that knowledge certainly should become evident after all this time on the road, the honest answer is to say you don't know -- and for them to discount all the polls of the moment. My strong belief is that the election could go either way, and won't be decided until those hours three weeks away when voters go through their final agonies before casting their ballots -- or deciding not to vote at all, which would hurt Carter more than Reagan.

Two voters encountered along the way seemed to sum up the quandary so many feel as they deliberate over whether to return Carter to the White House. One, a young farmer from Illinois, was undecided but leaning away from the president, whom he supported before. "He hasn't done anything for us," he said, "and he's let things get out of control." The other, a young Idaho college student who is registered and plans to vote, leans toward the president. "Carter doesn't deserve a second chance," she said, "but he deserves it more than Reagan deserves a first one." Not exactly the most ringing endorsement, but if there are enough like her it could be the path to another four years.