NEVER MIND THAT there will be epic struggles for control of state houses and fierce battles for congressional seats all around the country this fall. We can think of no political contest more important to citizens of the nation's capital than the Sept. 12 Democratic primary contest that will decide, for all practical purposes, who will be mayor of the District of Columbia for the next four years. Today we embark on an effort to sort out the issues and the candidates, to reach some judgements on the values that ought to weigh most heavily in the final decision - and to arrive at a choice.We propose to do so step-by-step, because a process of elimination strikes us as the most manageable way to go about it.

So let us begin - and not in any frivolous way - with the two also-runners. Dorothy Maultsby and John Ray, it seems to be agreed, don't matter because neither one of them is going to be mayor; by that test, it is true, that they are not really in the race at all. But their contributions to the campaign entitle them to more serious attention than they have been able to attract. Their significance does not lie only in their potential for draining off just enough votes to tip the balance decisively in a three-way race that could conceivably be excruciatingly close. It lies as well in what they have brought to the debate: energy, conviction, seriousness of purpose, constructive provocation, and a fresh approach unburdened by old associations or responsibility for what has been done - or left undone.

To a far greater degree than any of the three principal contenders - Mayor Walter Washington, City Council Chairman Sterling Tucker, and Council Member Marion Barry - Mrs. Maultsby and Mr. Ray can honestly promise a change. There is, about their forlorn efforts, an appealing us-against-them quality, a capacity to stand back and take a hard look at the conduct of the city's business over the past four years, or more, because neither has had a day's experience as an officeholder in the District government.

They are, then, the purest personification of what this campaign is really all about: The urgent need for new energy, a new sense of commitment, a new and better way of doing things at City Hall. This is not to suggest that the Big Three are not promising to do things differently - and better, naturally. Even the incumbent, while trumpeting his achievements in office, is conceding the need for some sort of change. But the officeholders must all, to some degree, reconcile bright promises with dim performances. No such contradictions trouble Mrs. Maultsby and Mr. Ray. And so in open forums and other confrontations, they are free to press questions about the convention center or housing policy or the budget or crime control that the insiders just might not wish to press against one another. That is their singular contribution to the campaign, and it derives from the advantage of not ever having been part of the problem.

But being outsiders, of course, also puts Mrs. Maultsby and Mr. Ray at a crippling disadvantage. For one thing, they don't always know enough about the problems to have very sensible solutions. For another, their campaigns languish for lack of public recognition - or the right connections. The word is that they're going nowhere, so nobody pays much attention, which makes the word a self-fulfilling prophecy.

It doesn't sound fair, and Mrs. Maultsby and Mr. Ray have said as much, wondering out loud what it takes to break into local politics. The short answer is that it is asking a lot to break in at the top. But the real answer is that they are breaking in and beginning to get better known. They are making small, but significant waves that could turn out to be very big waves if the election is close. They have been speaking forcefully for change. In the process, they are pressing the principal candidates to give some better definition of their own thinking about the changes they would make. And that - for us, at any rate - is the central question of this campaign.