Perhaps the most important political decision to be made this year is the selection of the Democratic vice-Presidential nominee. President Johnson suffered a massive heart attack nine years ago. Actuarial statistics show an alarming mortality rate among men of the President's age after the first five years following such an attack. Even if Johnson survived one or two terms, a fairly young and active vice-President would be a leading contender for the party's nomination in 1968 or 1972.

A seasoned Washington commentator said recently that "if I had to bet more money than I can afford to lose, I would bet on Sargent Shriver for the nomination." He listed three reasons for his choice. First, he said that President Johnson wants to retain the loyalty and active support of the Kennedy family and of Democratic politicians throughout the country who still feel a deep allegiance to the late President. Johnson does not want, the commentator said, to put Robert Kennedy on the ticket. Therefore Shriver, who helped construct the Kennedy machine in 1960 and has good personal relations with many "Kennedy men" in the party, appears to be the only other man who can keep the Kennedy machine intact.

Second, he said that Johnson appreciates Shriver's background in business, a background which would season him for the tough political maneuvering in which Johnson revels. As Murray Kempton recently put it in The New Republic, Shriver was the only man Joseph Kennedy trused to collect his rents at the Merchandise Mart in Chicago.

Third, the commentator said that Johnson is extremely impressed by the job Shriver has done with the Peace Corps. His enthusiasm is increased by the fact that Bill D. Moyers--a 29-year old White House staff member whom Johnson greatly admires--actually wants to return to the Peace Corps, where he was second in command.

Shriver's chief handicap is that he is not extremely well known and has never held elective office. Johnson understands this deficiency. He made Shriver director of the war on poverty partly to increase Shriver's reputation and political stock.

Whether Johnson chooses Shriver, then, depends on how desperately the President thinks he needs him to hold the Kennedy machine. And too, it depends on Johnson's assessment of Shriver's capacity to be a good President.

This latter standard will be applied by Johnson and by the public to every prospective candidate. Speaking on television Wednesday night, Walter Lippmann said that no candidate could help Johnson significantly at the polls. Therefore, Lippmann said, the only criterion for selecting a vice-Presidential nominee should be his qualifications for the Presidency.

If this criterion is used, the best Democratic nominee would be Sen. Hubert Humphrey. Humphrey wants the nomination. He has solid support from labor (although labor has not often proved to be a solid political force). But Humphrey might be too valuable to Johnson in the Senate. Sen. Mansfield, called by some "his own worst critic," reportedly will cede the Majority Leadership to Humphrey in the next Congress. Paradoxically, then, if Humphrey is outstanding in handling the civil rights bill he could impair his own chances to be vice-President.

What of Robert Kennedy? Reports of a feud between him and Johnson are probably overdone, but it is no secret that the two have never gotten along. There is a vast difference between the two in style, personality and temperment, if not in policy. According to reliable reports, Johnson will choose Kennedy only if political conditions make it imperative. Kennedy may go after the nomination, at least in private. But he will have to accept Johnson's choice. He is young and if he decides to make politics his career, he cannot afford to alienate too many men he might rely on in the future.