It is retirement time for many of those holding public office. The end of the year will mark the end of careers in politics stretching back, in some cases, to the 1940s.

Of the many who are stepping down this year, six seem particularly significant for the contributions they have made. Three are members of the House: Rep. John J. Rhodes (R-Ariz), a member since 1952 and, from 1973 through 1980, minority leader, Rep. Richard Bolling (D-Mo.), a member since 1948 and the chairman of the Rules Committee; and Rep. Henry S. Reuss (D-Wis), a member since 1954 and chairman of the Joint Economic Committee. Three are governors, all past chairmen of the National Governors Association: Robert D. Ray (R) of Iowa, who has been governor since 1968; William G. Milliken (R) of Michigan, in office just a few months less than Ray; and George D. Busbee (D) of Georgia, completing eight years as that state's first two-term governor.

It is not just their longevity that makes them leaders, but that is part of it. In a time of overweening ambition, when so many of their colleagues viewed the possession of one public office simply as a springboard to another, these stayed at their work. All six of them passed up chances to run for the Senate, that showcase of egos.

They are, of course, distinctive personalities. Milliken and Rhodes, despite their Yale and Harvard educations, are models of humility who have led by self-effacement. On the other hand, Bolling, who once served on Gen. Douglas MacArthur's staff, suffers fools about as gladly as did his onetime boss.

Ray and Reuss are regarded in their communities and among their colleagues as examples of personal integrity, as much esteemed by opponents as by their fellow-partisans. Busbee, who moved from the legislative leadership into the governorship, has a genius for negotiation and consensus-building that is all the more striking when contrasted with the lack of those skills in his more famous predecessor, Jimmy Carter.

All of these men are first and foremost successful politicians. The understated line in their biographies, "Reelected in this and this and this year," speaks volumes. But they are much more than that.

They are what Bolling calls "institutional men," as much concerned with building the capacity of the governmental instruments of which they are a part as they are in advancing their careers.

Milliken, Ray and Busbee all have enlarged and redefined the role of governors in their states, and of the governors association in national policy-making. Bolling and Rhodes, among other achievements, were major contributors to the design of the congressional budget process.

All six brought formidable intellectual abilities to their work, often in areas where there was little political reward for expertise. Not for them the one-page, boiled-down summary of a staff member's research. What they thought it important to learn, they really learned. Reuss made himself an authority on the monetary system and the Federal Reserve Board long before most of his colleagues in Congress knew either had any importance.

But more than intelligence, they brought to their daily work an enlarging vision of their own responsibilities. They overcame the parochialism of politics and showed by example to both colleagues and constituents how they might take a larger view of the world. They have been teachers as well as leaders.

Bolling, a product of the University of the South, stood with Speaker Sam Rayburn of Bonham, Texas, in maneuvering the first civil rights bills in a century past the roadblocks erected by die-hard southern opponents in the House.

Rhodes, whose Republican partisanship is as deep as his family roots in Kansas, stood tall during the trauma of Watergate, and helped his fellow Republicans understand that their obligation to the Constitution overrode any claim of party loyalty.

Milliken, who grew up in a wealthy, privileged family in lovely and isolated northern Michigan's Traverse City, battled endlessly to put the resources of his state -- and the concern of his party -- behind the struggle for survival of the people of Detroit.

And Bob Ray, in Des Moines, somehow translated his concern for the refugees of America's war in Southeast Asia into what was probably the most successful emergency feeding and permanent resettlement program in the United States.

In a time when many view politicians with deep suspicion, the integrity, ability and durability of these men are a powerful rebuttal to cynicism.