If a skyscraper is planned in Arlington that could be seen from the West Front of the Capitol, whose business is it to determine how high it should be--Arlington's, or the federal government's?

If a development is to be built next to the Suitland Parkway (which is operated by the National Park Service) and the development blocks the scenic view from the parkway, is it in the federal interest to ask Prince George's County to modify the project?

These and other questions formed the core of one of the liveliest "summit" conferences held here in years. It was conducted by an ad hoc committee representing the two caretakers of metropolitan planning in this region--the National Capital Planning Commission for the federal government and the Metropolitan Washington Council of Governments, for the local governments.

The group's mission was to define where the federal interest begins and purely local interest ends in planning. In any other part of the country, this might be little more than an interesting academic exercise, tantamount to determining how many angels can dance on the head of a pin. But in the Washington area, the subject is a deadly serious matter.

In general, planning is the sorting out of a myriad of competing interests in some rational manner to meet the "public interest." But in this region it is further complicated by the variety of "publics" whose interests are being addressed. Who, after all, are we planning for-- the Arlington, District of Columbia or Montgomery County citizen who lives here, works here, pays taxes here and commutes to a job here? Or are we planning for Mary Smith from Iowa, who sees the nation's capital as her second home town, as the federal city that she pays taxes to support as well?

For local elected officials, the question is a simple one to answer. Yes, they respect the beauty of the monumental city, they certainly appreciate the significance of the enormous federal presence here, and, in most cases, the federal interest is something they can easily accommodate, especially because it often meshes with the interests of their citizens. But for these same elected officials, the ultimate concern is the voter, and the local interest. These officials have to be concerned with creating jobs and housing for their constituents, all the while balancing precarious budgets and revenues. This sometimes conflicts with historic preservation, or with efforts to enhance views from federal buildings.

For those responsible for federal planning, the job becomes one of preventing those "local rascals" from putting a townhouse development on the Washington Monument grounds or an industrial park in the middle of Arlington Cemetery. Although these federal planners, too, usually can accommodate and often do encourage certain local goals, such as creating jobs or strengthening the local economy, their objective is to preserve the federal city that Pierre L'Enfant envisioned--and to see to it that the city meets the needs of the federal government.

As in almost any good Washington conflict, defining the federal interest boils down to an interagency battle over turf. It heated up when members of the Council of Governments thought the Planning Commission was invading the domain of local planners by telling Arlington that its buildings were obstructing the view from the Capitol steps. These and other actions prompted many angry exchanges over the role of the Planning Commission and the "true meaning" of "federal interest"--which is what the Planning Commission cites to get involved in these local decisions.

As may have been anticipated, the ad hoc committee never did define the federal interest. Instead, it set out a number of guidelines to be used to determine which bodies of law or policy should take precedence in different situations. It also came up with suggestions for better cooperation between regional bodies in the future.

Like so many "summit" conferences, this one did not quite accomplish what it set out to do. But at least the participants did agree on some rules by which local agencies could operate, some order in which proposed planning changes would be reviewed by all the various parties. And if these don't work, there is always the threat that Congress might get more directly involved.

So maybe peace will prevail again in the world of regional planning--for a while. And eventually another generation of graduate students and planners will kick around the concept of "federal interest" and conclude that, like pornography, "I can't define it, but I know it when I see it."