For the third straight election, the managers, pollsters and media strategists for the presidential candidates gathered this past weekend, under the friendly auspices of the Institute of Politics of the John F. Kennedy School of Government at Harvard University, to review with each other the decisions they made while they were adversaries.

Representatives of three Democrats, six Republicans and one independent who sought the presidency were brought together for the weekend. It was, for the most part, an extraordinary demonstration of the essential civility of the relations among political professionals in this country, a mixture of good manners and genuine camaraderie that would baffle anyone from a society where politics is viewed as a form of personal or ideological warfare.

The substance of the round-table discussions must remain private, under the ground rules, until Harvard University Press publishes the edited transcript of the conference in book form next summer.

It will make interesting reading. But for those of us who watched the conference unfold, the real fascination was the personal chemistry among the victors and vanquished, as they reviewed a struggle that played so central a part in all their lives.

Some of Jimmy Carter's key players did not come, the role reversal from 1976 apparently being more than they could publicly endure at this point. But those who did -- including such key figures as Tim Kraft and Pat Caddell -- were generous in their admiration of the winning Reagan strategists, led by Bill Casey, Richard Wirthlin, Peter Dailey and Lyn Nofziger. So were the representatives of the various losing Republican contenders and so was the man who called himself "the biggest loser of them all," John B. Anderson.

In that respect, the atmosphere of this conference was much more like that of 1976 than of 1972. In 1976, the admiration for the Carter group's acumen came unforced from defeated Republicans and Udall-Jackson-Brown Democrats alike. It was very different in 1972, when the shadow of the unfolding Watergate story clouded discussions between the McGovern and Nixon forces, and no one could mistake the tensions between the secretive Nixon group and their supposed fellow-partisans from the Republican National Committee.

This year's conference resembled 1972's in only one respect: the enmities between rival factions inside the Democratic Party are very sharp after this defeat, just as they were after the McGovern rout eight years ago. The most emotionally tinged exchanges in the meeting involved Carter and Kennedy spokesmen, reliving and re-justifying the tactics they used on each other in the winter primaries and in the summer maneuvering that kept the nomination fight going until the August convention.

Since this was a gathering of political professionals, it will not surprise you that the hero of the weekend, the man whose work was most widely and spontaneously praised, both at the table and in private conversations, was Republican National Chairman Bill Brock.

His comments on the developments in the Republican nomination battle, the convention and the fall campaign were sparing but exceptionally candid. They struck me as the words of a man who had done the job he hired on to do superbly well and felt completely secure about his own place in the political history of this period.

Without bragging, Brock can claim that from 1977 on, he kept Republican eyes focused on the economic issue and led an unprecedentedly well-conceived, well-organized and well-financed media and political campaign to use that issue to break apart the old Democratic coalition.

With powerful reinforcement from the equally disciplined and focused Reagan campaign, Brock saw his efforts achieve the greatest Republican victory in a generation.And he did it in a way that won admiration untinged by bitterness from the Democrats he defeated.

Bob Keefe, the Democratic pro who had a large hand in the 1976 Tennessee campaign that defeated Brock for reelection to the Senate, told him here, "I think I did your party a favor by making you available for the chairmanship." The one thing on which the quarreling Democrats might agree is that they would like to find -- and hire -- a national chairman like Bill Brock.