THE DECISION OF D.C. Democrats to replace three incumbent D.C. Council members with an old-school city politician and two political newcomers is likely to have a direct impact on the course that the city follows in the months ahead. The defeats of Harold Brazil (at large), Kevin P. Chavous (Ward 7) and Sandy Allen (Ward 8), though not unexpected, mark the loss of experienced legislators who had a direct hand in the city's financial recovery and economic resurgence. That each was accused -- successfully -- by opponents of ignoring constituent interests is a lesson for the rest of the council and for Tuesday's Democratic primary victors -- provided, of course, the latter win in the November general election.

Clearly Kwame R. Brown, who defeated Mr. Brazil, amply demonstrated that he was the superior campaigner, with the kind of energy, determination and people skills that voters were looking for in a challenger. The same might be said of Vincent C. Gray and the winning campaign he waged against Mr. Chavous in Ward 7. Sandy Allen in Ward 8 lost, pure and simple, to a name that is golden east of the Anacostia River -- Marion Barry. The question the whole city may be asking at this time is what Mr. Brown, Mr. Gray and Mr. Barry would bring to the council in January, should voters give them the nod in November. It must be a question that is also haunting Mayor Anthony A. Williams (D) and his administration.

It would not be quite accurate to say the primary elections were a referendum on the mayor's policies. But it is worth noting that the economic development course charted by the Williams administration enjoyed the general support of the three defeated incumbents. Based on the campaigns they conducted, challengers Barry, Gray and Brown may be more inclined to move in the direction of community and neighborhood development, with less emphasis on the huge downtown projects of which the mayor's economic team seems enamored. In addition, Mr. Barry and Mr. Gray were and continue to be outspoken champions of defunct D.C. General Hospital. The mayor should expect added pressure from the trio on the health care, housing and social services fronts. Jack Evans (D-Ward 2), also a primary winner, and his tax cut allies on the council should not expect much help from Messrs. Barry, Gray and Brown.

The greatest challenge now facing the mayor and council Chairman Linda W. Cropp (D) is to keep the District on the fiscal track that has produced seven balanced budgets, positive Wall Street ratings and steady economic development even as they seek to accommodate the legitimate policy and program interests of the council's soon-to-be new faces. No easy feat indeed, but not mission impossible either.