With the nomination of Walter F. Mondale for president, the Democratic Party has moved full circle. Twelve years after Sen. George McGovern opened the party to the amateur activists and eight years since Jimmy Carter emerged as the politician who lambasted the political establishment, the nation's oldest party has returned control to its professionals.
Officeholders were ''frozen out of the apparatus, and now we're back,'' declared a triumphant House Speaker Thomas P. O'Neill Jr. at a fund-raising luncheon on the closing day of the 1984 Democratic convention, in which members of Congress played the most active part in many years. In all, 208 members of Congress were delegates, compared with only 45 at the 1980 convention.
The deliberate effort to give elected and party officials a higher profile included setting aside 14 percent of the delegate slots for them.
These 568 ''superdelegates'' were not bound by their local primaries in picking the party nominee, and they overwhelmingly sided with the man they had known for many years, former Vice-President Mondale. Without their votes, Mr. Mondale might not have won on the first ballot.
Also, at least partly because of the experienced political hands, the Democratic convention, which had a potential for splintering into its many subgroups, ended without a major flare-up.
Democratic Party pros who had longed for a ''dull'' convention saw their wish largely fulfilled, as they toiled behind hotel suite doors to resolve problems that might have spilled into the convention hall and prime-time television.
In fact, the superdelegates helped dowse a controversy that started even before the opening gavel, over Mondale's attempt to replace the Democratic National Committee chairman. Amid an uproar of protests that threatened the harmony, it was a California congressman, Tony Coelho, who served as peacemaker.
House and Senate members played key roles in ironing out platform and rules compromises. And the coup de grace came when Rep. Geraldine A. Ferraro of New York rose to prominence through her post as platform committee chairman and became the party's vice-presidential nominee.
For all the glowing reports from many party leaders, however, their return to power in the party is not universally applauded.
The superdelegate system ''wasn't very democratic,'' says Lee Harris, who served as an Illinois floor leader for Sen. Gary Hart. ''It was structured so people on the inside have a dominating effect on the selection of the president.''
The system also dilutes the power of the party's many subgroups, from environmentalists to nuclear freeze advocates.
Critics of the superdelegates have already won passage of a recommendation that the next party reform commission cut their number in half. But Democratic leaders are so happy with the current system that they are resisting the cutback and have already won an agreement to delay any action until after the November election.
Even some Hart supporters say they liked the superdelegate role. ''I think it would be terrible if we changed the rules,'' says Rep. Martin Frost of Texas, one of Hart's earliest backers. He adds that participation gives the elected officials ''a stake in the campaign'' and a reason to fight for it.
Although the Rev. Jesse L. Jackson had argued for doing away with all superdelegates, one Jackson delegate applauded the inclusion of elected officials. ''I think the superdelegates are a political reality,'' said Ohio State Sen. Bill Bowen. ''You need those persons who have the wherewithal to get out the vote.''
As for the superdelegates themselves, they often described their role as that of firemen ready to hose down flames if needed.
For the most part, the alarms did not sound at the convention.
And that was exactly the way the party pros wanted to begin the 1984 campaign.