At a public hearing last week, the National Capital Planning Commission reviewed the conceptual site and building plans for "access improvements, plaza and buildings" at the Kennedy Center. This attempt to expand the arts center and better integrate it with its site has been in planning for some time, and will take years to complete. However, this meeting was a key step in the process.

Several witnesses and the D.C. Office of Planning questioned many aspects of the project. After testimony and discussion among commissioners, the commission voted to approve the concept.

In light of the concerns expressed, especially by the Office of Planning, and the immensity of the project, the commission discussion seemed perfunctory, and the vote to approve the concept seemed rushed.

The project applicants, the Federal Highway Administration and the Kennedy Center, pointed out that the conceptual design process has been underway for more than a year, and nods of preliminary concept approval have been received previously from D.C. officials and the Commission of Fine Arts. The applicants are understandably "disheartened" that the Office of Planning is now expressing reservations.

The planning office's somewhat delayed reaction may be a bit untimely, but in the overall time frame, this delay is minuscule. More important, the response is justifiable, well reasoned and thoughtfully articulated. This project's scope, complexity, impact and cost -- a whopping $400 million just for redoing the roadwork and building the deck -- are enormous. By the time the project is completed, its cost is likely to exceed half a billion dollars.

Whatever is ultimately done will affect this part of the District profoundly. Therefore, now, while the changes are still in the concept formulation stage, is the time to fully consider -- and reconsider -- the transportation, urban design and architectural options, and their consequences.

The project has two main goals: improving vehicle, transit, pedestrian and bicycle access to and movement around the Kennedy Center; and creating a new deck and plaza spanning the Potomac Freeway on the east side of the center, with two new buildings on top of the deck and framing the vast plaza.

Before the hearing, the planning commission staff and executive director reviewed the proposal and recommended concept approval. But in their report, in response to many of the D.C. planning office's concerns, they also directed the applicants to undertake 31 alternative design explorations, revisions, modifications and enhancements -- a record number of recommended items, according to the planning commission staff.

Some of the recommended changes would have little effect on the substance of the concept. Several, though, are significant. Among them:

* Improve and maximize connectivity to the existing city fabric and street grid for vehicles, pedestrians and bicyclists, especially those arriving from the north and east.

* Reduce the size of the plaza.

* More effectively bring activity to the plaza while reducing roads and vehicle traffic in the plaza.

* Reposition new buildings atop the deck to allow future development of adjacent, mixed-use structures.

* Configure new buildings to enhance views of, and into, the Kennedy Center complex from surrounding areas and from the Roosevelt Bridge.

* Redesign the Potomac River overlook on the west side of the Kennedy Center to ensure unobstructed views from the terrace, and to improve connections to the waterfront and Rock Creek and Potomac Trail.

To illustrate what such revisions might entail, the D.C. planning director, Andrew Altman, appeared at the hearing accompanied by his office's urban design consultants, Ehrenkrantz Eckstut & Kuhn. EEK principal Stanton Eckstut presented a graphic analysis of the city context in relationship with the Kennedy Center and suggested a number of alternative design strategies.

Casting the urban design net more widely, EEK showed the Kennedy Center strongly linked to the Lincoln Memorial, visually and symbolically, by means of a continuous, formally composed landscape, in effect bending and extending the Mall's axis northwest to the Kennedy Center. Shown were stronger ties to Foggy Bottom, with New Hampshire Avenue leading directly to and from the Kennedy Center without pedestrian-unfriendly obstructions.

EEK also showed how development of new buildings and a vehicular plaza could act as the western end of Virginia Avenue, create a spatial gateway to Rock Creek Park and resolve the currently messy confluence of park, streets and Whitehurst Freeway ramps north of the Watergate complex.

Some of EEK's proposals, although potentially good ideas, are clearly beyond the scope of the current project and beyond the control of the applicants. But reducing substantially the size and shape of the grandiose, overscaled Kennedy Center plaza, and increasing development density and uses around the plaza, are both feasible and desirable.

Presumably, with concept approval in hand, the applicants and their consultants will take into account these suggestions as they proceed further with design. Yet last week's commission hearing posed implicit questions that frequently arise when projects are submitted for conceptual design review. What is the exact meaning of "concept"? How much or how little does concept approval limit subsequent design evolution and flexibility? At what point do post-approval design modifications change a concept sufficiently to cast doubt on the original approval?

Let's hope these questions fade as the Kennedy Center project sponsors revise their concept to comply with the planning commission and planning office recommendations. Let's also hope that they, as well as the commissioners, recognize that last week's vote does not mean that the approved concept needs only tweaking.

Roger K. Lewis is a practicing architect and a professor of architecture at the University of Maryland.