IT SAYS ALMOST everything about Walter Washington's candidacy for reelection that it should rest so heavily on excuses. His was the first administration to try to govern under limited home rule, you are regularly reminded, and in a lot of ways it's just too hard. Congressional control over the budget, you must realize, denies real self-rule and makes long-term planning impossible. Civil Service guarantees of job security carried over from the transition period have confounded earnest efforts to reorganize and revitalize bloated bureaucracies. And so the explanations run on...and on. Whenever the government hasn't worked, you must try to understand, it's been the system's fault.

As campaign arguments go, that one doesn't exactly race the pulse. And yet, we do not doubt that, with a lot of people, it stirs a certain sympathy. When self-government is a brand new experience, how can you be sure that the way Walter Washington has been governing the city isn't the way it's supposed to be?

Well, perhaps you can't be absolutely sure. We would no more minimize the hard problems that faced Mr. Washington four years ago than we would question the depth of his commitment and concern. Still less would we deny him full credit for his considerable contributions to the well-being of this city, tracing back to the difficult early days of transition when he was the first appointed mayor. A good case can be made that he was very much the right man to lead the District of Columbia into limited home rule, and had well earned the right to be the city's first elected mayor in 1974, and to try his hand as the head of a popularly elected city government under a whole new, and necessarily experimental, system of self-rule.

But that was four long, troubled years ago. And the question now turns entirely, or so it seems to us, on whehter you think Walter Washington and his well-entrenched team of ideas and advisers have made the most of those four years. Are all the failings and shortcomings of those years really owing to some intrinsic flaws in the rules and arrangements imposed by Congress? That's what the mayor seems to be saying - half of the time. But if that is the case, is it realistic to expect him to be able to make good on his campaign promises of changes for the better, reform of this and reorganization of that, of improved performance all around - the promises he's now making the other half of the time?

It will come as no surprise to you that we think the answer to both questions is No. We don't believe the present, limited system of home rule, as much as we'd like to see the limitations removed, can reasonably be blamed for most of what's gone wrong in the past four years. We don't believe, in other words, that Walter Washington has been running the city government nearly as effectively as it could be run right now - even without some larger grant of autonomy from Congress. And since Congress can't be counted on to relax its budgetary control anytime soon, in any case, we see no reason to believe that Walter Washington would find it any easier to deal with the city's most pressing problems over the next four years than he has in the last four.

So it comes down to what you think of the mayor's performance in the last four years - and also what you consider the city's most pressing problems to be. Mr. Washington sees a city, unlike a lot of other cities, that pays its bills and doesnt't run deficits, which is true enough; Congress wouldn't have it any other way. He sees general prosperity and a sudden new burst of economic activity and housing rehabilitation by developers in run-down inner-city neighborhoods - and takes credit, naturally, for those good things and others that have blessed the community in his first term. He sees a "solid record of achievement" and claims that "what I have brought to you is a dignity and a commitment that I think no mayor anywhere can match."

What we see is a record of genuinely scandalous mismanagement of the Department of Human Resources, the government's largest entity, with one-fifth of the population of the District looking to it for services.

We see a chronic inability to monitor and manage welfare payments, an epidemic of errors in Medicaid payments, federal grants lost irretrievably because applications were sloppily handled.

We see persistent insensitivity to conditions at Forest Haven and Junior Village and D.C. General Hospital and D.C. Jail.

We see corrective court orders ignored.

We see government-owned housing boarded up and unused in the midst of a grinding shortage of lower-to-middle-income housing.

We see no real strategy to deal with the wave of housing speculation in a way that would ease the plight of the dislocated and dispossessed.

We see intolerable levels of unemployment among black youths.

We see no sign of official awareness of an astonishing increase in arson in this city - let alone an effort to do anything about it.

We see the same inexplicable inaction with respect to an alarmingly high infant-mortality rate.

We see, in other words, a full catalogue of incompetence and negligence and indifference, no part of which has anything much to do with an overbearing Congress or with Civil Service strictures. What it has to do with is inertia. We are talking about an administration hunkered down, fixed in its ways, incapable of summoning the spirit or will or nerve or imagination to deal with the problems of those citizens in this city who need its help the most.

The mayor's main argument against his challengers is that they lack his experience. That's true. But is misses the point. Experience, in the full sense of the world, is not an argument that works in favor of Walter Washington.