The endorsement game went out of fashion in Democratic presidential politics in 1972, but it is likely to be revived -- with a vengeance -- in 1984.

In that 1972 campaign, Edmund S. Muskie, then senator from Maine, collected early pledges of support from so many notables that he seemed unstoppable. But the Muskie endorsements crumbled before the grassroots appeal of the two Georges -- McGovern, the eventual nominee, and Wallace -- and Muskie wasn't even around by the time the primaries were finished.

From that day, the value of endorsements in the Democratic Party has been discounted as deeply as Penn Square Bank stock is today. In 1976, Jimmy Carter positively gloried in the absence of endorsements as he powered his way to nomination, and in 1980, the sudden fadeout of some big-name Democrats who had encouraged him to run did not keep Ted Kennedy from pushing his challenge right into convention hall.

But that pattern is likely to change -- and change dramatically -- now that the AFL-CIO executive council has approved federation president Lane Kirkland's plan to try to find consensus on a candidate endorsement at a December, 1983, meeting of the unions' general board.

It is not certain there will be a consensus; the plan requires a two-thirds vote, with each union president casting a single ballot weighted to his union's membership.

But the very existence of the Kirkland plan changes the dynamics of the Democratic contest in fundamental ways. No one can ignore -- or discount -- a pre-primary endorsement by the AFL-CIO. Union members surely will not vote as robots for the endorsed candidate. But the endorsement carries with it, not just blessings and good will, but money and propaganda and a ready-made campaign machine in every state.

At the very least, the Kirkland plan makes mincemeat of all the talk among Democrats about shortening and reducing the cost of the next presidential nomination campaign. A party rules commission sweated and strained last year to move the first Iowa caucuses back five weeks from late January to late February, 1984, and the first primary in New Hampshire back one week from late Februapy to early March.

But the December, 1983, AFL-CIO meeting now becomes at least as important as either of those postponed events. And it will not be the first such landmark on the way to nomination.

ao legitimize its president's vote at the December meeting, each international union wil, have todevise some method of sampling the sentiments of its own leadership and membership. That means that a convention of the steelworkers or machinists -- or any other big union which will exercise heavy influence under the weighted voting system -- becomes as important to the candidates as the North Carolina or Massachusetts primary. Candidates -- and reporters -- will have to learn as much about the internal dynamics of a big UAW local in Dearborn or AFSCME in New York City as they do about the characters in Black Hawk County, Iowa, or Dade County, Fla.

It will be a fascinating game. Kennedy and former Vice President Walter F. Mondale are regarded today as the main contenders for endorsement, but Sens. Alan Cranston and John Glenn will have leverage on the decision whether to endorse at all, if only because their home states of California and Ohio have such heavy union membership.

They are not the only players, nor is this likely to be the only endorsement game. The AFL-CIO decision puts pressure on other mass-membership organizations to make their own endorsements -- perhaps ahead of the labor federation's vote.

Take the National Education Assn., which had more delegates at the 1980 Democratic convention than any AFL-CIO affiliate. The teachers' group does not want to let Kirkland and Co. preempt its choice. So already there is informal discussion of "recommending" a candidate for the primaries at the September or December, 1983, meeting of NEA's 120-member board.

A recommendation is a step short of a formal endorsement, which applies only to the general election and can be made only by the full NEA convention. But a board recommendation of Carter in September, 1979, put the NEA political machinery at his disposal and proved a vital factor in his defeat of the Kennedy challenge in the primaries.

What labor and education groups do will have an impact on environmental organizations, women's groups, black and Hispanic organizations -- and may stimulate endorsement contests among them.

The net effect is likely to be to push intensive Democratic presidential politics into a much earlier part of 1983, as the candidates vie in a two-tier system, first to be endorsed, and then to prove or disprove the endorsements' value in the 30-plus primaries that still await them in 1984.