THE TIME HAS COME to realize that we do not need another book unveiling Jimmy Carter's character. The president has long since shed his psychological clothes, primarily in his autobiography, Why Not the Best?, published as his campaign soared out of oblivion in 1975. One of the most telling self-portraits written by someone whose ambition was not only to be famous, but to be elected to public office, Carter's book laid out his flaws and strengths so candidly that most later assessments of the president as a man would use his own revelations to make their case either for or against him.

Still, even if Jimmy Carter had not volunteered his past, we would have asked. He rose to national fame in an era when we suddenly began worrying about a president's formative years and wondering what made Richard Nixon's face tic. By 1976, Americans were still reeling from the uncomfortable images of Nixon roaming demonically through the White House, talking to the portraits on some occasions and ranging altogether too close to the apocalyptic button on others.

Moreover, if American voters wanted to know what Jimmy Carter was like as a human being, it was also true that there was little else to know at the time about him. Emerging from a political nowhere called Plains, Georgia, he had been governor of his state for one unspectacular term. The country could not examine Jimmy Carter's national record because there wasn't one.

Now, as the nation struggles this election year to judge Carter in a different way -- to determine this time how well he has done on the job -- Bruce Mazlish and Edwin Diamond have given us yet another assessment of what he is like as a person. For those of us journalistic buzzards who enjoy every tidbit in a presidential past, there are a few new vignettes. But for most people, it will quickly become apparent that Mazlish, who wrote a well-known psychohistory of Richard Nixon in 1972, and Edwin Diamond, a senior political science lecturer at MIT, have simply spread a layer of parlor psychology over shopworn facts. Ultimately, the book reads like another version of Why Not the Best?, rewritten by a recent Esalen graduate.

For example, Mazlish and Diamond do not do much to forward the cause of psychohistory -- an academic field not held in particularly high esteem among historians in the first place -- with their analysis of why Carter has a deep and abiding love for the underdog. It is not primarily because he is a Christian, we are told, nor is it because battling for the underdog has been a tradition in American politics ever since it became apparent that the underdogs had all the votes. Instead, the authors have concluded that Carter has a deep respect for the little people primarily because he is short: "Jimmy Carter, the man, has a genuine empathy with the little men of the world, those on the bottom rung of society," the authors explain somewhat witlessly. "It comes, we believe, from his own self-image. Carter has overcome his smallness by becoming a David among Goliaths."

The authors also trace Carter's intense competitive streak to his demanding father, Mr. Earl, for whom perfection seldom seemed enough from his oldest son. For those who have followed Carter for years and written extensively about how his lips tighten in anger even when he loses a softball game, this is an all too familiar facet of the president's personality. Mazlish and Diamond do, however, report on a little known incident -- Carter's failure to win a coveted Rhodes Scholarship after his graduation from the Naval Academy -- and, by giving the president's own description of his victorious rival, they elaborate on a certain pettiness Carter is often unable to control.

"He [the rival] studied Elizabethan poetry, and the interviewing board asked him something about current events, and he said he wasn't interested in anything that happened after Queen Elizabeth died," recalled Carter who remembers also that he himself told the same board about everything from nuclear technology to philosophy.

"The other kid got the Rhodes scholarship. I didn't even feel bitter about it," the president said. Then he added, "As a matter of fact, he went over there from Georgia and he had a nervous breakdown."

It is classic Carter -- a man able to behave so graciously to the lowly and the forlorn and yet equally capable of suddenly shedding his Christian forbearance in order to land one last kick on a competitor of 30 years before.

By contrast to the psychopolitics of Mazlish and Diamond, Finlay Lewis, Washington bureau chief of the Minneapolis Tribune, has written a sturdy, unpretentious and quite fascinating biography of a more difficult and less overworked subject, Vice President Walter Mondale.

Mondale is dearly loved by most reporters because he has the rare abilities (for a politician) of being able to laugh at himself and to keep his ambitious edges reasonably under wraps. And he emerges from Lewis' book as a perfect vice president, not altogether a political compliment.

Tracing Mondale's career, Lewis adroitly unravels a political history that is some ways the opposite of Carter's. Mondale, unlike the president who is still fighting old contests, could lose his battles and move on. Lewis tells of the time Mondale was gaining in a 220-yard dash during the final meet of his high school career, when he suddenly stopped 20 yards short of the finish line. "I said, 'What the hell, there's no point in this -- I'm not interested in this,' and I just quit," Mondale recalled.

Later, Mondale would do much the same thing when he backed out of a campaign for the presidency in 1974, joking afterwards to reports that he was tired of the decor in the nation's Holiday Inns.

Lewis portrays Mondale as an extremely charming and witty man but also a party loyalist, a follower of orders, a number two who doesn't try harder to be number one -- which, one suspects, is why Mondale has succeeded so well in getting along with Jimmy Carter these past three years. For the highly competitive Carter, Mondale has carefully kept out of the race. Unlike other politicians (especially Jimmy Carter), Mondale has made his biggest political strides by being appointed to offices, not running for them. He was first appointed attorney general in Minnesota, then senator to replace Humphrey in 1964 and then in 1976, Carter picked him to share the ticket. "Walter Mondale is a survivor," Lewis concludes. "Some races have been impossible to win. Sometimes winning has been knowing when to walk as well as when to run."

In passages that sometimes sound almost rueful about a man who undoubtedly is the author's friend after all these years, Lewis reveals the side of Mondale that always makes his admirers uncomfortable: He tends to have a streak of political cowardice.

Once, when they were out fishing together, his friend and then Governor Karl Rolvaag lost control of the boat because he had been drinking heavily. Mondale, after helping Rolvaag to a nearby cabin, left to catch a plane as had been previously planned. "He was obviously leaving so he wouldn't get involved in any way," said Congressman John Blatnik, (D-Minn.), who encountered the much shaken Mondale that day at the airport. "The guys told him to leave, and he probably wanted to leave anyway."

Later, a similarly timid Mondale would back his mentor Hubert Humphrey in Humphrey's defense of the Vietnam war, bringing intense criticism from his liberal friends. After Mondale had an emergency appendectomy in early 1967, one of his old allies in Minnesota remarked, "I hope they stuffed him with some guts before sewing him up."

Lewis, nevertheless, presents Mondale as a decent man, given the profession he has chosen. What Lewis has done is to give us a strong sense of the vice president by carefully recording the facts of his life and then, unlike Mazlish and Diamond, not limiting his analyses to nodules on his subject's head. There are no psychological gimmicks, it is simply a solid, well-written and well-documented book.