To many Washingtonians, "floating zone" may sound like an innvoative defensive strategy employed by the Redskins.

But it is rather one of many zoning strategies adopted by cities and counties during the past several decades and intended to facilitate innovative, flexible land development and design.

In the 1950s and '60s, separation of homogeneous uses and precisely prescribed geometrical constraints seemed too obstructive for increasingly sophisticated planning, architectural, financial and market concepts.

Zoning and master planning were accepted as legalized instruments of public policies only distantly related to protecting "health, safety, welfare and morals." Achieving economic, social and aesthetic goals were legitimate grounds for zoning and for new zoning tactics.

In fact, many communities, especially suburban ones, had tested the bounds of zoning legitimacy. "Exclusionary" zoning had effectively separated socio-economic classes by limiting subdivision lots to one, two or more acres. Low- or moderate-income homes were unlikely to appear because the costs of acquiring and improving such large lots were substantially greater than improving lots containing 5,000, 10,000 or 15,000 square feet.

During the '60s and '70s, judicial actions overturned exclusionary zoning in specific cases and locations. Plaintiffs argued that such zoning was clearly discriminatory and effectively reinforced existing patterns of segregation by race as well as by economic and social status. No protection of the public interest could be shown, they claimed.

But local governments could use zoning for positive economic purposes. By encouraging and enabling certain types of development to occur in a community, government could augment its property tax base, increase business and employment activity, and thereby enhance economic opportunity and growth.

Of course, more intense land use or higher density does not always lead to improved fiscal conditions. Sometimes, new development can result in greater demand for municipal services -- schools, roads, road maintenance, police and fire protection, utilities, trash collection and other administrative support. If the additional costs of providing these services exceed the additional tax revenue generated, the fiscal impact is negative.

For example, neighborhoods with town houses and homes of modest size are likely to attract young, middle-income families with school-age children. Because public education is usually the largest single governmental expense, this type of development will have greater fiscal impact than zoning targeted for singles, couples, the elderly or the affluent. As a result, many jurisdictions have tried to shape their zoning ordinances to control the demand for, and cost of, urban services.

Industrial parks, office buildings and certain kinds of retail activity usually produce a net positive fiscal benefit. However, they can generate new and serious traffic and parking problems whose costs are indirect. For some neighbors the nuisance deficit may outweigh the tax surplus.

Much recent zoning reflects aesthetic policy. Developers, architects, planners and government officials believed that imaginatively written zoning ordinances could provide incentives for designing and constructing better environments. Most believed that this was virtually impossible using traditional Euclidean zoning based solely on constraint.

Once again, New York took the lead. After World War II, Manhattan's skyline and skyscrapers were characterized by the "wedding cake" look. Buildings rose straight up from the sidewalk at the property line, then stepped back incrementally as they rose higher and higher to an often exuberant silhouette or spire. This was a direct expression of the mandated zoning envelope, intended to ensure adequate light, air and sky view.

Setting back the whole building could create a public plaza, an amenity perceived to be lacking in New York's canyon country. But the developer would have to sacrifice leasable floor space, for the building's "footprint" and gross area would be smaller.

So planners and zoners came up with incentive, or trade-off, "bonuses." As motivation and in return for making a plaza and a thinner building, it seemed both fair and economically indispensable to allow such buildings to reach higher and contain even more square footage with increased FAR (floor area ratio, a comparison of building space with land area).

The presumption was that certain amenities -- plazas, arcades, courtyards, atria -- rarely would be included by developers seeking to maximize their investment returns on traditionally zoned property by filling the zoning envelope.

Thus, if the body politic could reach consensus on which amenities were worth having, then zoning could become a "quid pro quo" process. In effect, zoning commissions and agencies could negotiate with motivated developers and architects.

Traditional constraints -- on density, height, setbacks, lot size and shape, and, most importantly, allowance uses -- could be relaxed in exchange for dedication of open space, easements, extra roads, elaborate landscaping, preservation of historic structures or special facilities for selected population groups.

Incentive zoning appears to serve public and private interests. But to maintain control over final results, most jurisdictions impose a multistep process to finalize the private-public "deal."

Unlike "matter-of-right" zoning which allows building to proceed without special reviews and approvals, most flexible zoning requires the developer to submit site plans and building designs for review prior to zoning approval and issuance of building permits.

This entails considerable risk. First, it can be costly and time-consuming, depending on numbers of reviews, notice periods required for public hearings, workloads of planning and zoning staffs, and the schedules of planning and zoning boards or commissions.

In some jurisdictions, final actioneven may depend on approval of the legislative council. And, after months or year of work, the final vote may be negative.

Second, there is the "cooks stirring the broth" risk: design by committee that yields camels instead of horses. At each step in the process, developer and architect are subjected to "input" from reviewers who willingly make suggestions about design characteristics of the project for which zoning is sought.

What are some of the zoning categories that typify incentive zoning, yet normally require layers of approval?

* Planned United Development (P.U.D.) zones allow a mixture of uses and buildings to occupy a single parcel of land.

* Cluster zones allow housing units to be aggregated rather than spread out on a tract so that the overall density of the tract remains unchanged; constructed density and infrastructure efficiency are increased, along with common open space.

* Floating zones, usually of intense and mixed uses, are not assigned in advance to particular lots. As if floating freely in space, they come down to earth only when applied for by an owner or developmer for a particular property.

* Conditional zoning, adjudged illegal by some state courts, grants zoning to properties contingent on the applicant meeting specific, agreed-upon conditions for development of the property.

* Special, or ad hoc, zoning is created by a legislative act establishing a new category only for special projects that otherwise could not be implemented under existing zoning.

Zoning has come a long way since the 1920s. Pamphlet-size zoning ordinances have turned into weighty sets of statute books. Specialized attorneys handle zoning cases. Architects spend dozens of hours researching, reading and interpreting regulations to figure out what they can and cannot design.

One wonders if it's all necessary, if the results justify the means. What might our environment look like witout zoning? No pun intended, but zoning may have its limits.

NEXT WEEK: Washington and Houston.By Roger K. Lewis; Roger K. Lewis teaches architecture at the University of Maryland and is a practicing architect.