THE SHADOW of Ivanhoe Donaldson at city hall has proven long -- and costly to the mayor. Marion Barry, surrounded with trouble, is presiding over an ungraceful exodus of top administration figures as well as the disciplining of other city officials involved in the Donaldson investigation. Where this will stop is far less clear than is the necessity for the actions Mr. Barry has just taken -- and for more complete airing of the details than the public has so far. The systematic fraud committed by former deputy mayor Donaldson required help from others who, even if they had no inkling of what was going on, might have been expected to question or resist unusual and -- often -- unethical requests and procedures on the part of a superior.

While it can be argued that these other cases should have been handled more swiftly, the mayor notes that his decisions first awaited a review by his legal counsel of evidence that federal prosecutors presented in the Donaldson case. Some of the evidence was in court papers filed in December and in a presentencing memo in January; the review submitted to the mayor also led to his determination that there were no grounds for disciplining four officials named in the prosecution documents.

Meanwhile, a grand jury investigation continues; among other things it is examining whether any of those who violated city administrative rules knew of the Donaldson fraud scheme at the time. For now, the situation is this: Department of Employment Services Director Matthew F. Shannon and Deputy Director James George have resigned, eight other department officials have been disciplined and the associate director for contracts has been designated for firing, which she is contesting. But what specifically did each of these employees do or fail to do? And what if anything more is there to report in the wake of another resignation -- that of Deputy Mayor Alphonse G. Hill after he ackowledged receiving a $3,000 payment from the head of an auditing firm that has received hundreds of thousands of dollars in city contracts?

Yesterday D.C. Council Chairman David A. Clarke and council member John A. Wilson came up with separate proposals for disposing of such questions. Mr. Clarke proposed a permanent "independent" government agency controlled jointly by the mayor and council; Mr. Wilson proposed a temporary special council committee to investigate. The Wilson proposal makes some sense. The council has a legitimate legislative role, and it has immediate authority to create a committee and get to work.

But there is no reason to create a new bureaucracy, as Mr. Clarke would do. There exists already an independent D.C. auditor, with power to demand information from any part of government and to issue reports. There are internal investigators in the executive branch who report to the mayor. There are representatives of the federal General Accounting Office who look at the city books. There are congressional committees that do this as well. It may be that more of this information should be made available to the council and to the public. Surely a special temporary council committee could seek answers to this and any other questions it might have.

If Mayor Barry is as determined as he says he is to root out wrongdoing at city hall, he should welcome serious help from the council.