Four of the last eight presidents have been men who served previously in the vice presidency. None of them much resembled the president under whom he served.

In office, Harry Truman was not at all like Franklin D. Roosevelt; Lyndon B. Johnson was not another John F. Kennedy; Richard M. Nixon was not like "Ike" Eisenhower; and Jerry Ford was not another Nixon, thank goodness.

That is not surprising, inasmuch as ticket- balancing is the main principle of vice presidential selection. That implies they are more likely to be opposites than clones.

The only reason to raise this rather obvious point is that it is in danger of being forgotten in the case of Walter F. Mondale, the former vice president who has emerged, with the withdrawal of Ted Kennedy, as the early favorite for the 1984 Democratic presidential nomination.

Half the articles one reads about Mondale's prospects quickly make the point that his chances are "clouded," to use the favorite word, by his having been Jimmy Carter's vice president.

It is certainly the case that Mondale is best known to the public, at this point, as Carter's two-time running mate and loyal vice president. To the extent that he shares the record that got Carter turned out of office in 1980, it is a legitimate point.

But, as Washington reporters know, the falsest reason one could have to support or reject Mondale is the supposition that he is another Jimmy Carter. Whatever he is, he ain't that.

The most powerful influence on Mondale's character and thinking was not Jimmy Carter but Mondale's Minnesota mentor and guide, the late Hubert H. Humphrey. And there are at least four other ways in which Mondale differs fundamentally, not casually, from Carter:

1.) Carter was a stranger to the national Democratic Party organization and many of its major constituencies when he was nominated. Mondale has been a party wheel horse, at the state level since 1946, and at the national level since 1964, when he negotiated the Mississippi delegation fight at the Democratic convention for Humphrey and Johnson.

2.) Carter was an outsider to Washington, skeptical of its practices and distrustful of its people, as his memoirs make clear. Mondale is -- Lord help him -- a favorite of the Washington establishment, which is one reason he was picked to balance Carter on the ticket.

3.) Carter was never at home with Congress. Mondale is a creature of Congress, a senator for 12 years and a popular member of its inner circle.

4.) Carter was never at home with organized labor or the liberals. Mondale, like Humphrey, has his political base with the teachers, the unions and the issue-oriented liberals.

Since the press knows this history better than the general public does at this time, we owe it to the public -- if not to Mondale -- to make the point clearly as the scrutiny of this man begins. That is particularly the case because there happen to be a lot of other important questions to be answered about Mondale. So many, that we should not waste much time on irrelevancies.

Here are three relevant questions about Mondale, for starters:

1.) Can a man who has risen as the loyal prot,eg,e and appointee of others be a leader in his own right? Mondale was appointed attorney general of Minnesota and senator before he had to run for either office. He was named by Carter as his running mate and carried into office with Carter. He was loyal to those who pushed him forward. But does he have an inner core of belief that will define and sustain his leadership without them?

2.) Can a man so steeped in the liberalism of the 1950s and 1960s and 1970s sufficiently free himself intellectually to provide the fresh answers needed for the 1980s? Did Mondale's brief sabbatical really invigorate his thinking -- or just his appetite for office?

3.) Do his powerful alliances with big labor, big education and the other big-government interest groups impose big constraints on his freedom of action? Is Mondale man enough to command his constituencies rather than let them run him?

These are some of the legitimate tests he faces in the coming months. He may be able to pass them all, for he is a man of talent as well as good will. But we ought to focus on those questions, rather than waste his time -- and the voters' -- trying to make him prove the obvious: that he is not another Jimmy Carter.