I live below the flight path along the Potomac River leading to and from National Airport, yet I think the airport's planned transformation, encompassing architectural preservation and expansion, is a good idea whose implementation is long overdue.

National Airport is undeniably here to stay, and it should look and work much better than it does. With quieter aircraft and, one hopes, improvements in both air and ground traffic control, the airport doesn't have to be a nuisance, a hazard or an eyesore. And how many airports are served by a subway that is among the world's most attractive urban transportation systems?

I admit to still having a boyish fascination with airplanes. Passing through airports, many of which have become self-sustaining minicities, I always feel compelled to figure out their diagrammatic organization and structural composition.

Big-city airports have become giant machines for handling complex flows of vehicles, people, baggage and aircraft. Conceptually, they are made up of two movement networks joined by a third element, the terminal. One side of the terminal connects to the ground network and accommodates people arriving or departing by cars, taxis, buses, limousines and vans. This network also includes vast quantities of parking. The other side of the terminal is for airplanes, along with their service vehicles and equipment.

Unifying these two networks of ground and air travel is the interior world of the terminal -- a network of lengthy concourses and sometimes cathedral-like spaces. Here passengers on departing flights buy tickets, check baggage, pass through a security checkpoint, wait in lounges and, when called, proceed through gates and ramps to aircraft.

The ideal airport diagram separates departing and arriving passengers, usually by different levels. Upper levels are for departures. Arriving passengers, after deplaning, are typically shunted down to baggage claim and ground transportation areas at ground level, facilitating distribution of baggage from aircraft to carousels to vehicles.

But there is more to the airport experience than just moving bodies and baggage. Passengers, plus those who transport them, may have to spend hours in terminals waiting for delayed planes.

Therefore, considerable amounts of space within airport terminals are devoted to restaurants, fast-food outlets, bars, cocktail lounges, gift stores, newsstands, bookstores, barber shops, post offices, branch banks and myriad boutiques selling everything from fine chocolate to hardware to freshly cut flowers.

If this sounds like a description of a shopping mall, that's what airports increasingly resemble. It's probably just a matter of time before we see airports that house department stores, food markets, real estate sales offices, dry cleaners and multiscreen movie theaters. One wonders what the Rouse Co. would produce if it could develop an airport.

The best airports are often the easiest to use and understand architecturally. The original version of Dulles International Airport, designed by Eero Saarinen, remains the simplest airport diagram ever developed, even with its dependence on mobile lounges for moving passengers from departure gates to planes. And Dulles' concrete and glass main terminal is still considered an architectural tour de force, a structurally bold shelter for terminal operations that symbolizes movement and flight.

Unfortunately, Dulles, like National, has outgrown itself. Greatly increased passenger volume has destroyed the smooth, effortless and almost elegant functioning of Dulles' main terminal. New, architecturally neutral midfield terminal facilities have been added, and the main terminal's lower level concourse and gates have been expanded. So many passengers pass through the original upper-level concourse that airport officials removed all the black leather seats because they impeded traffic flow. There now are only a few seats left in Saarinen's great hall.

Finding a parking space, at least in the same county, also has become difficult at Dulles. National Airport has had the problem for years. The rule seems to be that when you're late for your plane, all lots are full. Like every other major airport, structured parking is a necessity, even with access to the Metrorail. The proposal for transforming National Airport seems to make all the right diagrammatic moves. The plan saves and rehabilitates the original 1941 art deco terminal, which would be linked to a new, linear, two-level terminal abutting the primary service road. Pedestrian bridges at the roof level span the road and connect directly to new parking garages and, most important, to the existing Metrorail station.

The now hazardous and unprotected walk of several hundred yards from the Metro station to terminals will be significantly shorter, safer and more comfortable in both summer and winter. More people would use the rail system.

National Airport, like a city in microcosm, has grown haphazardly over the last 46 years. Buildings were added and remodeled ad hoc, with little concern for their relationships to other buildings. Roads have been rerouted and parking reconfigured to improve circulation, but no integrated master plan seemed to guide what was happening in totality, either on the exterior or interior.

Moving through some of National's terminals is a mazelike experience. One continually has to make lateral and vertical shifts in direction, turn corners and climb up and down stairs. Colors, decorative motifs, the style of signs and lighting change unpredictably. Coping with layers of vehicles in drop-off areas is perplexing and dangerous for pedestrians and drivers. Perhaps the layout is intended to prepare motorists for driving in Northern Virginia.

National Airport's future architectural details are yet to be developed, but they probably will reflect current airport design trends -- modern, structuralist, high-tech, function-specific, if not expressively symbolic. And Washington's neoclassicism is unlikely to manifest itself. An airport, so totally a 20th century, technologically inspired phenomenon, seems inappropriate for historical allusions to ancient monuments.

Whatever the case, National Airport must be made workable and commodious. With good design, it actually might become a delightful place at which to look, catch a plane or even get stranded.

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