WHAT WILL the downtown Washington of tomorrow look like? According to a grand overview produced by the Mayor's Downtown Committee after more than a year's intensive study, the shape of the city in many respects may resemble that of an office building--over and over again. In the crystal ball of this committee are many corridors of office buildings, even though it is unclear whether all of them will have people working inside.

That is only one feature of the draft produced by this group of residents, business representatives, developers, architects and other people who agreed to take on this planning assignment. The value of the study is, as Post architectural critic Benjamin Forgey has written, that it exists. It is "a document, something identifiable and written down that we can argue with and--cross your fingers--change."

There is no question that a comprehensive plan for the District is necessary if there is to be any coherent relationship between land-use decisions and zoning policies. And one will be completed in a matter of weeks. The big question is whether downtown Washington will be the region's prime center of offices. The committee sees a hefty increase in the number of offices and jobs by the year 2000--which may well occur--but much will depend, of course, on what policies are adopted in the suburbs.

With a little imagination, the suggestions of the committee can be turned into a valuable start on the long-awaited comprehensive plan for the entire District. And it need not be taken as a cue for rows of dull buildings that look like computer punch cards. Luther H. Hodges Jr. of the National Bank of Washington, who served as committee chairman, points out that "many cynics and critics of the private sector look at the cranes in the air over the downtown and say the city doesn't need a plan and added bureaucracy for developing downtown. But we want a plan . . . to avoid sterile office-complex development."

Along these lines, the committee is proposing a design-review agency with authority to set standards and have broad powers over zoning, architectural design and historic preservation. This, when you consider the number of agencies now involved in these functions, may take a minor miracle to occur in anybody's natural lifetime. But the concept is sound.

When you glance up from this report, however, there is something called reality--and in development, it still turns out to be piecemeal planning. You need look no further than the site for Metro Center, at 12th and G Streets NW. The history of the city's attempts to dispose of this valuable property--it's been a decade, now--is a tale of governmental inertia and paper-lock. At this point, a Superior Court judge has ruled that the cit acted improperly when it revoked the right of developers Oliver T. Carr and Theodore R. Hagans to proceed with their project. The argument is over the price tag for the land--and unless negotiations bring some agreement, the dispute will drag along in the courts.

In planning, haste may make waste--but a coordinated hurry could help no end.