Theoretically, you can still apply to be a Democratic presidential candidate for 1984. But in practical terms the field is closed. Sens. Ernest Hollings and John Glenn, who announced this week, are the fifth and sixth candidates to do so this year.

Sen. Edward Kennedy announced last fall that he would not run, and there is no sign of a groundswell calling on him to change his mind; Sen. Dale Bumpers, who looked like the seventh candidate, withdrew last month. Other candidates have announced earlier in the two-year (or is it three now?) campaign cycle before: Jimmy Carter while he was still governor of Georgia in 1974.

But never, in our recollection, has the field been so effectively closed. County chairmen, campaign consultants, caucuses and unions are all looking over the candidates, making their endorsements, and plotting their own paths to the national convention on the assumption that these six men will be the only serious Democratic candidates.

It's natural to question whether these are the six Democrats most fit for the office. But every time you're tempted to say this is the worst field the Democrats have presented, just remember the New Hampshire primary debate in 1972, when Sam Yorty debated Vance Hartke, and Hartford antipoverty worker Edward Coll dangled a rubber rat on national television.

Some people are troubled by the fact that none of the Democrats running is currently shouldering any great responsibility for the ongoing conduct of government. Walter Mondale and Reubin Askew are, theoretically at least, lawyers in private practice. Alan Cranston, Glenn, Gary Hart, and Hollings are Democratic members of a Senate in which all major decisions are made by Republicans, and Democrats are free to vote unburdened by the obligations of a majority party. Yet all have, at different stages in their careers, shouldered major responsibilities, acting and making decisions under great pressure in full public view.

The lengthiness of the campaign process has in effect imposed a new requirement for the office: that a candidate first gain experience in office and then enter what Erik Erikson calls a moratorium. At the worst, that can be a period where a candidate's reflexes grow flabby and, freed from the discipline of having to make decisions that count, his instincts for pleasing everyone take over. At best, it can be a period when a candidate reflects maturely, takes counsel from a broad range of people and reacquaints himself with the gritty reality of life in the country he seeks to govern.

How well these Democrats have exercised their public responsibilities and how much advantage they have taken of their moratoriums are subjects we will all, thanks to the earliness of their announcements and the apparent closing of the field, have plenty of time to ponder. And we will have the chance as well to guess whether each of them--or any of them--has that instinct for governance that is essential for presidential success, and impossible to pinpoint precisely in a candidate.