Debate over proposed zoning amendments for creating a new "living downtown" in Washington's old downtown is separating idealists from realists.

Idealists enthusiastically support the proposal's most controversial provisions of requiring and offering incentives to developers to construct housing along with office buildings, retail stores and arts facilities in the area south of Massachusetts Avenue, east of 15th Street and north of Pennsylvania Avenue.

Having a populated downtown is indispensable to creating a "living downtown," an explicit goal of the District's adopted comprehensive plan, idealists say.

Without downtown housing, the idealists say, the central business district will never be a secure, vibrant, 24-hour destination teeming with cultural, recreational, civic and commercial activity. Unless people reside downtown, the District's streets will be lifeless during evenings and weekends.

Realists are just as adamant in opposing the housing proposal, not because they don't share in the ideal and its aspirations, but rather because they know the numbers don't work. To them, the ideal isn't attainable given what land, construction and financing cost today.

Mixed-use plans sound great on paper, opponents say, but the economic facts show that reasonably priced housing isn't feasible. Urban housing costs more per square foot than commercial space and yields much less rental income. Even the District loses, they argue, because a square foot of housing generates less real estate tax revenue than a square foot of commercial property.

Some engaged in the debate -- call them realistic idealists -- want commercial developers to build or pay for housing, but not downtown. They argue that downtown housing will only be affordable to the well-to-do and will contribute nothing to solving the District's real housing problems. For them, housing efforts should be directed toward constructing or rehabilitating dwellings for the needy in existing residential neighborhoods.

Finally, after months of negotiation and hearings involving the District Office of Planning and the D.C. Downtown Partnership, the D.C. Zoning Commission soon must reach a decision: Should zoning regulations require housing in commercial zones within the downtown development district? Should downtown developers have the option to build housing elsewhere or to contribute funds for affordable housing developed by others -- nonprofit sponsors or public housing agencies? Should office building developers alone shoulder this burden?

In fact, it is unrealistic to believe that creating a "living downtown" is only a matter of land use regulation. Making the zoning commission the sole focus of the debate likewise seems to be a misplacement of responsibility in light of the non- land-use implications of the proposed zoning overlay.

The reasons for wanting downtown housing are valid, despite idealistic intentions. However, satisfying these intentions requires more than zoning ordinances, which are necessary but not sufficient. It requires feasible methods of implementation coupled with substantial financial subsidies.

Thus, the downtown plan is realizable, but only with a public commitment of money, something over which the zoning commission has no control. It requires political leadership, also beyond the commission's control. And it could require a sacrifice of development rights and loss of economic value, which no private property owner or developer is likely to accept willingly, even if advocated by the zoning commission.

Call it what you will, the pending downtown zoning overlay could constitute downzoning. Are the politicians, the courts and the public ready to endorse downzoning? Creating housing downtown might necessitate condemnation. Are the politicians, the courts, and the public ready to support condemnation?

Free-market economics, coupled with current zoning adopted in the distant past, set the stage for the controversy.

The downtown zoning now in effect stipulates allowable types and maximum intensities of use, and the market value of zoned property reflects this maximum use potential. Therefore, switching part of the allowable density from commercial to residential diminishes the preexisting value of the property and, in the eyes of the law, may be a "taking" of property or curtailment of property rights.

Therefore, to avoid claims of downzoning or condemnation, which could require substantial monetary compensation, the District would offer developers compensation in other forms to make up for decreased value or loss of future revenues.

The bonus incentive approach grants the right to build mixed uses, including housing, at a density greater than that allowed for commercial use alone. The transfer of development rights approach allows selling unused commercial density to designated "receiving" zones -- properties approved for transferred density increases elsewhere in the District.

Unfortunately, these approaches have drawbacks. Neither addresses the problem of profitability in developing downtown housing, even with no land cost attributable to the residential footage. Neither ensures housing affordability. And both assume that the District can increase densities at will on properties when, in fact, such density increases may be publicly opposed for reasons unrelated to the desired production of housing.

The zoning commission's decision-making would be much easier if it knew that public support for housing in general, and downtown housing in particular, were forthcoming, along with public investment. Even developers would be more receptive to downtown housing if they felt that they alone weren't expected to pay all of the economic freight.

Perhaps the zoning commission would feel more comfortable if the city had a clear, comprehensive, proactive housing policy, if its programs were effectively meeting housing needs both downtown and in the neighborhoods. But that feeling of comfort is unlikely to come when thousands of housing units stand vacant and neglected, tenant waiting lists for badly maintained, poorly managed public housing lengthen, and budgets shrink.

Washington Post staff writer Rudolph A. Pyatt Jr. recently commented on the increasing shortage of affordable housing for employees of companies throughout the Washington area, not just downtown. He reported on studies pointing out how the expense of housing is making it difficult for private businesses, government agencies, schools and colleges to recruit new staff.

Yet are Washington's businesses, public institutions and private citizens prepared to to subsidize part of the cost of building housing for the employed middle class on whom the city and region depend for economic survival? Shouldn't some of this housing be downtown as well as in the city's neighborhoods and suburbs? Why not treat housing as a regional, multi-jurisdictional problem transcending zoning?

Whatever their decision, the zoning commission will take much of the heat, though not deservedly. They should be able to consider and advocate downtown housing in the context of plans for District and region of land use, transportation, housing and public investment, and these plans should embody high ideals achieved through realistic means. But not this year.

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