The continuing debate in Montgomery County over transferable development rights (TDRs) calls to mind again the inadequacies of traditional zoning in shaping cities and suburbs.

The TDR program, recently restored by the county council's unanimous vote after a court ruled the earlier program invalid, allows developers to purchase zoning rights to build houses on properties in one part of the county and transfer them to designated properties in other parts of the county. Shifting unused development potential from still rural to already urbanizing areas ostensibly preserves the open space and rural character of outlying county lands, at least for the moment.

The TDR strategy has been used elsewhere, and not only to transfer rights from county to city. Within some cities, density shifts from one property to another nearby property have been negotiated between developers and property owners with the sanction of municipal authorities.

The TDR idea is an ad hoc, remedial tactic. It was invented to overcome the inability of most conventional zoning laws to anticipate growth pressures along with changing travel patterns, economics, technology and social values.

Historically, zoning arbitrarily predetermined an inventory or a quota of density, expressed as floor area or dwelling unit limits, distributed in some presumably rational way throughout a jurisdiction. Time passed and conditions changed, yet original zoning laws changed little. Instead of rethinking the law, people have tended to look for legal loopholes or end-run opportunities that, like TDRs, allow piecemeal readjustment of original land use and zoning assumptions.

Recently, a number of American cities, dissatisfied with traditional zoning and patchwork development, have begun to reassess and restructure the way urban planning, land use and architectural design are regulated, particularly in their downtown areas. In some cases, they have adopted extremely radical, controversial policies and statutes governing growth and design that go far beyond zoning.

In part, they also are rejecting the laissez faire, let-the-market-dictate approach to city evolution. They have decided that more is at stake than increasing the tax base, creating jobs and boosting economic activity.

With substantial citizen support, interventionist jurisdictions have stretched the envelope of constitutional "police power," the right of government to protect public "health, safety and welfare." They have chosen both to control growth and to determine precisely where, when and how new growth will occur, including what it looks like. And they are using the "police power" simultaneously to meet social, economic and aesthetic goals.

Such cities believe they have a unique, recognizable identity with physical and cultural characteristics that must be preserved and extended. They believe in making plans with specific urban design intentions. And they believe that it's constitutionally defensible, under the same theory that justifies zoning, to insist that standards of design quality be met.

Although none has tossed out its old zoning maps, some cities have added enough new rules so that, in effect, they've created a whole new city plan and protocol for building. Admittedly, court challenges also are cropping up.

What are some of the new approaches to zoning being adopted in cities like San Francisco, Miami, Boston and Seattle?

Overlay zones. Planners and lawmakers are inventing totally new zoning categories and stipulations to be superimposed on areas previously zoned. While sometimes more liberal in allowing later variety and mixing of uses, they also may be more prescriptive and demanding about what is built, or restrict what can be changed or torn down.

Mandated preservation. Laws are being passed requiring that specific buildings, collections of buildings, neighborhoods, streetscapes and views be preserved. Demolition of designated structures or neighborhoods without extraordinary justification is outlawed. Tree protection ordinances also are being passed.

Mandated environmental quality. New regulations are addressing rights of access to sunlight, prevention of unwanted glare and shadows, and effects of new buildings on pedestrian level wind patterns. Of special concern is the impact of new buildings on the microclimate of public open spaces -- parks, plazas and courtyards.

Mandated architectural quality. Some cities are adopting regulations focusing not only on building bulk, height and setbacks, but also on roof shape and profile, graphics and signage, use and occupancy of sidewalk level spaces, street wall design and facade character. Design review and approval, necessitating inevitably subjective judgments, are being required as more design review commissions are formed.

Growth caps. Among the more draconian measures being adopted are specific, quantitative ceilings on the amount of development, particularly commercial space, permitted within specified districts and time periods. These seem to be driven by concerns over traffic, parking, office vacancies and market absorption rates and the timely availability of adequate public services and infrastructure. Assessing more carefully how each project contributes to the collective urban fabric has slowed the rate of new development.

Exactions. Some jurisdictions "exact" from developers specific contributions -- fees or other consideration -- whose purpose is to help provide necessary, public-interest urban services or facilities, such as low-income housing.

Confirming zoning to planning. Increasingly, cities are passing legislation requiring that zoning be consistent with adopted master plans, and that steps be taken to modify or abandon old zoning accordingly. This can represent a significant change in a city's future growth to the extent that new plans are generated. However, if master plans primarily reflect patterns of land use and zoning already established, as in the District, then such mandates may have limited practical effect.

The search for innovative growth management strategies, the consideration of unprecedented planning and zoning ideas, seems inevitable as people become increasingly worried about the livability of cities, preservation and urban and architectural design quality.

It's exciting to see such experimentation and risk-taking. Yet there is a downside. In more aggressively managing growth and advocating high standards of design, cities run the risk of stifling growth and compromising economic, as well as cultural and social, revitalization.

It's premature to judge most of these new efforts, but it will be interesting to watch.

Next: The San Francisco experiment.

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