It is the essential things one remembers about a place when away from it for a while -- Washington's low skyline, its proud symbolic monuments at the center, the wonderful setting of river and mostly green hills -- and it is a treat to come back and find that nothing important has changed. Yet.

Late last summer, as I was leaving for nine months in Japan, I read a report in The Post's business section about a 50-story building that might go up on the Maryland side of the Potomac, south of the city. Not a good idea, I thought, and left, hoping that somehow it would go away.

Of course, it didn't. The idea has been fleshed out by its notable creators, Philip Johnson and John Burgee, in the design for a a 52-story crystalline skyscraper, envisioned as the striking centerpiece of the PortAmerica world trade center and residential complex just outside the Beltway on Smoot Bay in Prince George's County.

In all major respects save one, the skyscraper is an appealing piece of work. Johnson, who turns 80 this month, and partner Burgee have designed and built a number of the country's more remarkable tall buildings in the past decade, and they know precisely what they are doing.

The faceted mirror glass cylinder they have conceived for the Washington suburbs will, if built, do what they intend: It will stand as a beacon above the rolling Maryland hills, subtly altering its appearance with each change in the ambient light, and saying, "Look at me." And the world will look.

The catch, however, is a big one. This is a building suited for a landscape in, say, Iowa -- in a place where it could shine alone, a contemporary version of the cathedral spire seen from some medieval wheat field. In its proposed location atop a knoll near the Potomac, just six miles from the city center, it promises to disturb significantly an esthetic balance that has characterized the region since the Washington Monument was completed more than a century ago.

Argument on this point takes visual form in a war of photographs going on between the National Capital Planning Commission and the principal developer, Virginian James T. Lewis, and his famous architects. Each side raised a helicopter to the height of the proposed building and each prepared montages of what the building would look like from various prominent points in the area.

Predictably, the images are wildly different and it may be that truth lies somewhere in between. The building may not turn out to be quite so visible from the monumental core as the planning commission predicts, but it is simply not credible that it will be, in Burgee's words, "a little bump on the horizon." Common sense alone is sufficient to conclude that a structure on the Potomac bluffs, 200 feet higher above sea level than the Washington Monument and 15 times its mass, would prove a major alteration in the regional skyline.

Is this something we want? I think not. I hope not. It is true that the center city model of the Washington area is fast being eclipsed by a multicenter metropolitan reality. The amazing pace and scope of Tysons Corner development is but the most extraordinary manifestation of this trend. It is also true, however, that we have something rare and beautiful here in the Washington region, and we have, through various actions of federal and local governments over the years, fought hard to maintain it.

This is nothing less than one of the great, prolonged feats of planning in the history of the world: the creation of a political and symbolic national center that has, despite all vicissitudes, maintained its basic structure for nearly 200 years. In this structure, it scarcely need be said, the topography of the Potomac hills plays an essential role. That these hills today appear, at least from a distance, reasonably close to what they were is something we should be proud of, and treasure. Is a world trade tower, even quite a distinguished one, more important than this history?

Of course, it would seem to be asking a good deal in the way of restraint on the part of Prince George's politicians -- restraint and some flint, as well -- to ask Philip Johnson, whose fearsome wit is almost as famous as his architectural skill, to go back to the drawing boards. But this is what they should, and easily could, do, for Johnson himself has supplied crucial clues to how the problem might commodiously be solved.

Though so far overshadowed by the skyscraper debate, the PortAmerica project, as distinct from the world trade center, is in many ways more challenging, more innovative and more instructive a piece of design. Johnson or Burgee would doubtless argue that the two go together, that their shimmering glass tower, located at the end of an arrow-straight axis a mile off the bay front, is the contrasting visual accent needed to tie the two parts of the project together. But a persuasive case can be made that the opposite is true: PortAmerica would look better and work better if the nearby world trade center were more in harmony with it.

PortAmerica is a residential-commercial complex located right on a pretty bay south of the Beltway's Woodrow Wilson Bridge. Its chief elements are 1,200 residential units, 176,000 square feet of retail space, one or two marinas, a ferry terminal and deep-water docking facilities, a waterfront hotel, community facilities, an inn, a lighthouse, many urban-scale parks, and a long, formal bay-front walkway that promises to be quite a regional attraction in a decade or so.

By designing this complex as a sequence of well-ordered spaces defined by rows of town houses and punctuated by crisp, solid volumes with spare, classical details, the architects demonstrate their awareness of national and regional architectural history, and also an exemplary consideration for the topography of Smoot Bay. It is quite a formal affair, this planned town, part suburb and part city, part London, part Charleston and part Alexandria, and it deserves (and will get, in time) separate consideration in this space.

Its relevance here is, simply, to pose the question: Why not develop the world trade center in a similar spirit? Not a similar style, necessarily, for differences in scale and use are obviously important, but in a way that treats the terrain, and its historic setting near the nation's capital, more sympathetically. Much more sympathetically. This cannot be too much to demand of designers as brilliant as Johnson and Burgee.

They'll yelp about artistic integrity and play to Prince George's County pride, but they must, or should, know they're putting their monument in the wrong place. They can, and should, do better.

What about it John? What about it, Philip?