IT HAS been said many times in many ways by D.C. Council members and candidates for mayor: the city's government work force is top-heavy with administrators. Now comes authoritative confirmation of this by an independent, bipartisan commission of private and government experts appointed by Mayor Barry to help the city develop a five-year fiscal plan. According to the preliminary findings of a commission subcommittee, the work force should be reduced by 6,212 positions during the next five years. That would represent an 11.5 percent decrease in positions authorized for the current fiscal year and a saving of as much as $196.8 million a year.

The committee has compared the fiscal 1987 staffing levels here with those of 12 other major cities for the same period. Even after adjusting for the fact that the D.C. government performs some state and county functions, the subcommittee found the number of workers here far higher. Significant reductions could be made almost immediately, the study finds, citing 4,979 positions that could be dropped through program changes and reorganizations.

This position-by-position study is subject to adjustments, because no report has been released and the findings are still to be approved by the full membership of the Commission on Budget and Financial Priorities, which is headed by Alice M. Rivlin, former director of the Congressional Budget Office. Some of the conclusions reportedly have become sensitive issues within the commission; it will not issue its final report until after the November elections. The numbers would not be net savings in any event, since there are certain agencies that experts say are strapped and could legitimately use additional positions.

But the importance of the preliminary report is undeniable. As John Wilson, chairman of the council's Committee on Finance and Revenue says, "it does establish the fact that we have a bloated bureaucracy," even though the Barry administration "keeps saying that we don't." The political challenge will be whether and how the recommendations can be carried out. In a city facing an estimated $90 million deficit for the current fiscal year, the payroll has got to be cut. The Rivlin commission is giving the next elected mayor not just a spur but also a sound basis for moving ahead.