IN A PECULIAR and deflating way, the mayoralty campaign in the past week has taken on precisely those characteristics that people have found so dispiriting in the administration of Walter Washington itself: Disillusionment, lowered expectations, exhortations to settle cheap, continued explanation of why nothing decisive or really good is ever possible, an attack upon hope and those who are foolish (or, it is said, reckless) enough to harbor it. That is the temper and spirit of Mayor Washington's government, and now it has become the awful, insidious mood music of Sterling Tucker's campaign: Come off it, Washingtonians, the siren song goes; don't you know that in this election you can't get the kind of real change you think the city needs? So come on . . . settle . . . play it cynical and safe . . . take second best.

We think that's the worst kind of argument - demeaning, defeatist, wrongheaded and unworthy of the terribly important opportunity the voters have. The District's Democrats in fact have a chance on Tuesday to vote for - and vote in - something better if they disregard that counsel of disillusion. We think that something is Marion Barry.

The question, of course, is what do you mean by change? Sterling Tucker apparently believes that anything that isn't Walter Washington is change. But that is true only in a self-evident, if politically irrelevant, sense. Mr. Tucker is not Walter Washington, but he's not all that different from him either - and that is the point. Consider a prime and central scandal of the Washington administration: its unwillingness or inability (or both) to deal honestly, compassionately and efficiently with the myriad clients of the Department of Human Resources.

DHR has surely been the mayor's worst show. And significant as the indictment and pending trial of Mayor Washington's appointee and friend, Joseph Yeldell, may be, that in fact is really the least of the DHR scandal. The DHR scandal is that agency's callous and chronic incompetence and indifference even to court orders to make it fulfill its obligations. The mayor uses the Yeldell indictment as yet another of his excuses: because this matter is before the courts, he claims, it would be somehow inappropriate for him to entertain conversation on the subject of the agency's terrible failures and derelictions over the years.

Mr. Tucker goes him one worse. He says he is "torn between reminding the people of the Yeldell incident" and his "personal feelings of not wanting to capitalize on someone else's misfortune." But he is evidently not "torn" enough to drop the issue altogether, for he goes on to warn ominously that Mr. Yeldell "will be back if he survives his trial and the mayor wins reelection." How's that for having it both ways?

But that's not the worst of it. Apart from this political turn, he conveys no awareness whatever of the magnitude, meaning and cruelty to its victims of the DHR disaster itself. Mr. Barry conveys intense concern. He has been proposing specific large changes in the organization of the agency. And he has also over the years been moved to visit personally the places DHR affects - for example, D.C. Village, Forest Haven and 20 of the 23 community-based health treatment centers. We cite this as a small example of something that is central to Mr. Barry's preferability to the other two candidates. He sees the city we live in and the government that presides over and (ideally) serves it not in terms of buildings or tables of organization or pieces of paper endlessly served up to explain why whatever it is can't be done - but, rather, in terms of real live people, some of whom have desperate needs and others of whom have a capacity to help them.

This is the kind of change we think the city needs and which we think Marion Barry, alone among the three candidates, promises to give it. And we think it is well within the reach of the electorate that will vote in the Democratic primary on Tuesday. The counsel of business-as-usual, half-a-loafism and take-what-you-can-get-you-can't-have-what-you-want add up to precisely the mood and method of governing that we now have a chance to reject and replace. It is our firm belief that it can be done with a vote for Marion Barry.