When approaches to land-use planning and control are considered, one tool many public and private groups have turned to is the easement, or limitation on the future use and development of a property.

An easement takes away some of the rights that come with a tract of land. Such interests often can be sold or donated to someone else. When those rights are contributed to a charitable organization, their value can be taken as a deduction for income tax purposes.

One of the biggest problems with either sales or donations of easements is deciding their true value, according to the participants in a seminar held this week in Warrenton, Va., to discuss "valuating" conservation easements.

The conference was put on by the Land Trust Exchange, a Boston-based association that serves as an information clearing house for "land trusts." Land trusts are private, nongovernmental organizations that work to preserve notable properties and special environments. The trusts accept easements on such lands and commit themselves to monitoring the properties in perpetuity. The Land Trust Exchange estimates that there are some 500 such groups around the country.

Land trusts, as well as local, state, and federal government agencies, are using easements in this region for a wide range of preservation objectives. Maryland has a joint state/county program to keep land in agriculture use by buying the development rights on it. Montgomery County has a program for farmers in one part of the county to sell the development rights on their agricultural land to builders who will use those rights to construct housing with a higher density in other parts of the county.

Along some sections of the Appalachian Trail, the federal government has purchased land easements to protect the right of way and the scenic character of the property next to the trail. Several historic preservation groups in the Washington area accept building-facade-easement donations from owners of notable structures. In all these situations, the preservation groups have found that purchasing or accepting donations of easements is a less expensive way of achieving their goals than buying properties outright.

Nevertheless, because an easement represents only a partial interest in a property, judging the value of such rights can be extremely difficult.

With other real estate, where there is complete fee-simple ownership, appraisal techniques are highly standardized. On any piece of property, appraisers use three basic methods for determining its value. A direct comparison with sales of comparable properties is generally favored. Another approach involves isolating the cost of the land and each of the buildings located on it. A third method, often used with agricultural and timber land, is to look at its income-producing potential.

Appraisers should use these same techniques in valuating properties with easements on them, according to Judith Reynolds, a Washington, D.C., appraiser who spoke at the conference.

The major problem comes from having to decide the value of a piece of property and its potential uses both before and after an easement is imposed. With land having limited development possibilities because of zoning restrictions or unfavorable topography, an easement may cause only a small diminution in value. In other cases, the loss may represent nearly the entire original value of the plot.

Only a small number of appraisers nationwide are experienced in doing these valuations, according to conference participants. Under the professional guidelines they must follow, appraisers are barred from assessing any unfamiliar types of properties unless they are working with a more experienced peer.

Doing a thorough analysis can be expensive, sometimes running several thousand dollars or more. While this is not a problem for higher income individuals with valuable properties, it can be a significant deterrent for middle-income individuals who wish to donate an easement to a charitable organization.

Faced with this dilemma, some individuals have chosen to use poorly qualified appraisers or individuals willing to inflate the value of the rights surrendered with the easement donation.

A land trust that accepts an easement in such a situation may not even be aware of the exaggerated value the donor is claiming. Charitable organizations traditionally have viewed the valuation of gifts to be a matter between the contributor and the Internal Revenue Service.

That practice drew fire from many of the conference participants, who believe land trusts should take a more assertive role in pushing donors to obtain accurate and complete appraisals in order to prevent land trusts from being viewed as merely abusive tax shelters for wealthy donors.

Pressures for improving easement valuation procedures also are coming from the Internal Revenue Service and the Treasury Department. In the last several years, the IRS has begun scrutinizing the tax returns of easement donors more closely in an effort to cut down on revenue losses from abusive and inflated contribution valuations.

Land trusts should focus more of their energies on self-regulation, said conference speaker William McKee, tax legislative counsel at the Treasury Department.

One of the first steps in this direction will be to develop written easement-appraisal standards to be used by both private organizations and government agencies. At the end of the conference, the Land Trust Exchange board of directors announced the establishment of a steering committee of attorneys, appraisers and land trust officials who will begin writing a basic manual detailing sound easement-appraisal techniques. No such text now exists.

Land trust representatives at the conference were optimistic that such standards will cut down on abusive valuation practices and preserve the integrity of their preservation efforts.

Land trusts "are saddled with blemishes because of problems with the appraisal process. That's unfair," said H. William Sellers of the Brandywine Conservancy of Pennsylvania. "There is a justification for private land trusts. They can do preservation work cheaper and faster than federal agencies."