The Democratic Party wound up one important piece of business last week and started another. The Democratic National Committee gave final approval to rules that will set aside about 550 seats in the 1984 convention--one of every seven--for elected and party officials uncommitted to any presidential candidate.

At the same time the party was giving this preferred status to its officeholders, another party commission was beginning the ticklish task of exploring how to hold those same elected officials accountable for the promises in the party platform.

The work of the new commission is unlikely to produce any result as clear-cut or dramatic in its political effects as the rule creating the big bloc of uncommitted delegates. But it illustrates the continuing tension within the party.

It is a tension between its politicians, who prefer a flexible, accommodating style of operations as the surest path back to power, and its more ideological interest-group supporters, who see the party primarily as a vehicle for promoting their own causes.

The officeholders tend to blame the issue-activists for pushing the party in the 1970s into support of policies that were outside the mainstream--and saddling it with presidential candidates who were rejected by most voters. That is why they demanded--and got--a bigger role for themselves in the next convention hall.

But the issue activists have not disappeared. Their energy, money and advocacy are still very important to the party, and their demands on its officeholders will not cease.

The resolution creating a "platform accountability" commission was pushed through the 1980 convention by the so- called Progressive Alliance, an amalgam of labor unions, civil rights organizations, feminist groups and other mass-membership organizations with their own, mostly liberal, legislative and political agendas.

Representatives of these groups dominate the commission, chaired by Yvonne Brathwaite Burke of California. Burke illustrates the kind of private agendas that flourish among commission members. Although she is a former member of Congress, she went to Dallas a couple of months ago to endorse another black woman who was running for the House against the Democratic incumbent.

Burke makes no apologies for her action, saying explicitly that she wants to see more women and blacks in Congress. But the incumbent, Rep. Martin Frost, is part of the House leadership who has fought the boll weevil defectors in his state, while Burke's endorsee had so little regard for party labels that she has subsequently decided to run as a Republican.

But the clearest example of the tensions in this territory comes from the commission's co-chairman, Terry Herndon, the executive secretary of the National Education Association. Herndon is an aggressive, outspoken liberal who has tried to turn the 1.7 million-member teachers' organization into a political machine for promoting a wide range of progressive programs.

Under Herndon, the NEA elected 302 delegates to the 1980 Democratic convention, and in many states so dominated the delegate selection procedure that it controlled other votes as well.

NEA has a very explicit agenda. To win NEA endorsement, a legislator must not only support large-scale federal aid to education, he or she must also oppose any form of aid to private or parochial schools.

Thus, in his NEA role, Herndon says he cannot, at this point, support someone like Sen. Daniel P. Moynihan (D-N.Y.), because of his advocacy of tuition-tax credits.

Yet the same Herndon, as a Democratic Party activist, is trying to instill what he calls "ideological substance" into the organization and persuade the politicians they should not automatically support just anyone who manages to win nomination as a Democrat. That kind of eclecticism, he says, "won't do."

The tension between the ideologues and the officeholders, the purists and the pragmatists, is not new. But it is particularly acute in today's Democratic Party, which has grown increasingly dependent on independent organizations, like the NEA and the unions, that have their own agendas.

If the Democrats are to function as a governing party, they need some method of dealing with those legislators who defect on critical issues of budget and economic policy. But equally, they need a method that will assure that their agenda for action is the party's agenda--and not just a compendium of interest-group wish lists.