Jimmy Carter was elected President only because of last-minute switches to him by moderate, independent voters, in the view of Carter's political pollster, Patrick H. Caddell.

In a memo written last December, Caddell suggested to Carter that these moderates, in addition to conservatives - "who have become a larger and larger bloc" - are key elements in the electorate. Failure to carry more conservative votes "jeopardized the whole election," Caddell said.

This analysis may help explain the cautious and moderate tone of the Carter presidency thus far.

Caddell agreed in his memo that large pluralities from blacks, union families, big city Catholics and the poor were crucial to Carter's victory, but he also suggested that these groups were inclined to vote for the Democratic candidate anyway. It was the moderate independents. Caddell said, who changed their minds in the closing days of the campaign in Carter's favor, putting the Georgian into the White House.

"A week or so before the election," Caddell wrote to Carter. "We were losing independent voters by as much as 10 points. Had that happened, we would have lost the election. As it was, we got about 47-48 per cent of the independents in the last-minute movement of the campaign."

Caddell's views were contained in a memo entitled "Initial Working Paper on Political Strategy," which was made available to The WashingtonPost this week.

Caddell attributed Carter's victory to votes from "nontraditional" groups, including women, better-off whites and Protestants. The pollster said Carter did less well than he had hoped among "the college-educated, white collar, middle and upper middle income voting groups," but nevertheless "he did better than Democrats traditionally have among these voters."

"However," Caddell wrote, "this group is growing so large that simply doing better than the past is not sufficient to guarantee election.If there is a 'future' in politics it is in this massive demographic change. We now have almost half the voting population with some college education, a growing percentage of white-collar workers and an essentially 'middle class electorate.'"

Caddell expressed concern that Carter did poorly with voters under 35 - carrying that group, "but only by a slight margin."

"These voters tend to be the least partisan and most liberal in the electorate," Caddell wrote. "We never seemed able to achieve any kind of visceral relationship with them."

Caddell noted that big northern cities, traditionally crucial for any Democratic presidential candidate, provided fewer votes in 1976 than previously, and thus were less important to Carter's victory. For example, Chicago used to cast more than a third of the votes in Illinois; last year it cast "only one-fourth."

Caddell said Carter had uneven success with women voters, though he ended up "running almost as well with them as we did with men." Many women had doubts about Carter's character, though they agreed with his positions on issues, Caddell said. "Noneworking housewives . . . were the bulk of the women with doubts," the pollster concluded, but "in the end many of them followed their instinct for change and selected Gov. Carter - cautiously."

Caddell told his boss that despite his Nov. 2 victory, he emerged from the elction campaign with four important weaknesses:

"1.Carter is still viewed as inexperienced.

"2. He is viewed as an individual who often flip-flops on issues and positions - a situation that we must be careful of, given the way the realities of government may force seeming changes in campaign positions.

"3. Carter was also viewed during the election as a person who 'overpromised.' There was considerable skepticism about many of his proposals.

"4. Most importantly, of course, is the general sense that Carter is a 'risk' as President. Because he is an 'unknown,' whose actions and behavior can only be discerned when he is finally in office, many voters worry."

Caddell called these four "the problems that the political activity of the administration must try to solve; they are the pitfalls that the administration is most likely to stumble in."

Caddell also lists some of Carter's post-election strengths, but starts it with the observation that "50 per cent of the public still does not know where Carter stands on the issues."

This could be seen as one of Carter's strenths, Caddell said, because "large parts of the electorate can project their own desires onto Gov. Carter . . ."

Caddell said Carter was perceived as a "strong leader with vision."

"One of his great strengths," Caddell continued, "is that he is perceived to be concerned about the average persons." The public also feels he brings a new sense of doing business to the government," Caddell said.