A flood of nearly 200 lawsuits filed last month by property owners, builders and developers in western Loudoun County illustrates dramatically how difficult it will be to implement conservation-minded, anti-sprawl land-use policies, especially in states such as Virginia, with strong private-property rights.

The lawsuits challenge recently adopted county zoning legislation curtailing development of hundreds of square miles of land between Dulles International Airport and the Blue Ridge Mountains.

Loudoun County supervisors, planning officials and many residents consider the new law a "smart-growth" plan. Opponents see it as a "slow-growth" plan at best and, at worst, as a "no-growth" plan.

Under the zoning regulations, overall residential density in western Loudoun County would be drastically reduced. Instead of one house per three acres, development would be limited to one house per 10, 20 or even 50 acres. The law provides density incentives for clustering homes to preserve open space and protect sensitive natural resources -- wetlands, streams, flood plains, mature forests, wildlife habitats, and aesthetically or historically valuable rural landscapes.

Plaintiffs claim that the law is a form of geographically discriminatory down-zoning that reduces property values, unfairly revokes vested development rights and represents unconstitutional taking of property.

By restricting the future supply of subdivision lots and homes, opponents further argue, the new zoning will result in rising housing costs. They assert that the law amounts to exclusionary zoning intended to safeguard the economic and social interests of "elitist" landowners in western Loudoun County.

The county has been wrestling with the sticky politics and rising costs of rapid population increase for more than two decades. Previous county growth-management plans and zoning changes have been chronically frustrated as attitudes shift and voters elect either pro-growth or anti-growth supervisors.

It's possible to sympathize with those on both sides of the argument.

On the one hand, many voters recognize the compelling need to wisely manage growth to protect the environment for future generations. Most citizens voice support for reducing air and water pollution, relieving traffic congestion, providing and maintaining quality public services, and combating unsightly sprawl. For some, smart growth is a moral issue.

On the other hand, put yourself in the place of an owner of property whose value has been instantly shrunk by half, two-thirds or even more. Imagine awakening one morning to learn that you are among those whose assets are substantially diminished by a new law. Is this fair?

Can these conflicting but legitimate interests be reconciled?

If they cannot, smart growth in the future is likely to be little more than a catch phrase. Litigation will persist as landowners, builders and developers ask courts and legislatures to uphold private-property rights, even though private-property rights and values are created by public policies and public investments.

Reconciling these conflicting interests requires achieving two objectives at once: implementing smart-growth plans and legislation to better use and protect natural resources for the benefit of society as a whole, and fairly compensating those property owners who lose vested development rights and suffer unreasonable financial loss because of government acts aimed at achieving the first objective.

There are basically two means for accomplishing this. Both are difficult politically and economically.

One entails direct or indirect use of eminent domain, whereby government pays property owners for lost rights, or buys property outright, using public tax money. This can be costly and is always contentious because it requires establishing fair market value for rights or for land based on a hypothetical assessment of future development potential.

The other entails transferring development rights from down-zoned areas to areas where greater density is desired, planned for, and supported by appropriate infrastructure and public services. This, too, requires establishing hypothetical fair market values for transferable rights.

Owners or developers of properties receiving additional development rights would purchase them at a cost based primarily on the location of "receiving" properties, not "sending" properties. In this scenario, a government agency or other fiduciary entity can act as a development-rights bank to financially bridge the time gap between purchasing and selling rights. This would be profitable for the public because the cost of acquiring development rights from a lower-density sending area typically would be less than the value realized upon subsequent sale and transfer to a higher-density receiving area.

To be fair and effective, a system for transferable development rights, commonly called TDR, must be regional in scale, adequately funded during start-up years, properly managed, and, above all, supported by detailed master plans that adequately justify and precisely designate sending and receiving areas.

For these reasons, relatively few jurisdictions in the United States have embraced TDR as a smart-growth planning and implementation strategy. And TDR remains a foreign concept in Virginia. Unfortunately, given the state's political culture and the legislature's constitutional dominance over local authorities, creating a workable TDR strategy in Northern Virginia would be an uphill battle, one that would have to be waged mostly in Richmond.

Yet it is a battle that must be fought if urbanizing counties really believe in smart growth. For the moment, only courthouse battles will be waged, defending against countless lawsuits like those just filed in Loudoun County. And even if Loudoun planning officials and lawyers have fashioned a zoning law capable of withstanding the litigation attack, the real struggle over coping with growth will have only just begun.

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