The IRS, in an action generally applauded by historic preservation advocates, has released proposed regulations governing the charitable donation of easements, or partial interests in land and buildings.

Nevertheless, the long-awaited rules leave largely unresolved the thorny question of what constitutes an accurate and fair appraisal of an easement. This is a major concern because donations of easements to nonprofit groups are tax-deductible.

"In general, with some modifications, the regulations look workable and they resolve some of the ambiguities of the statute," commented Allan D. Spader, executive director of the Land Trust Exchange, an association of land conservation groups that accept easement donations and monitor them in perpetuity.

The proposed regulations, released by the IRS on May 23, cover changes Congress approved in the Tax Treatment Extension Act of 1980.

Easements have been used for many years by conservation groups seeking to protect open land and special natural environments. Several U.S. government agencies, including the National Park Service and the Fish and Wildlife Service, routinely purchase such partial interests. This approach is less expensive than buying properties outright in order to preserve them.

An easement limits what an owner can do to the property. With a piece of land, it often means not being able to build on it or to change its current use. With an historic building, an owner is usually barred from tearing it down or from changing its exterior appearance. These restrictions bind not only the original easement donor, but also all subsequent owners.

Limiting a property's development potential causes a decrease in its value. An individual contributing an easement to a charitable organization can claim a tax deduction equal to the decrease in value caused by the easement's restrictions.

In several areas around the country, including Washington, the IRS has been conducting extensive audits of individual taxpayers and partnerships that have made easement donations. In many cases, the IRS has disallowed much of the easement deduction value claimed on tax returns. In a few cases, the IRS has declared the restrictions caused absolutely no diminution in the property's worth.

The proposed regulations only briefy discuss the appropriate methodology for appraising easements. When possible, the IRS says, sales of other properties with easement restrictions on them should be used for comparison. Where no such data are available, the value of the tax deduction for the easement donation will be the difference between the worth of the property before and after the limitations are imposed upon it.

While continuing to prepare their formal comments on the IRS' proposed regulations, several land conservation and historic preservation groups are working on alternative approaches to dealing with the easement-appraisal question.

In early March, the Land Trust Exchange announced the establishment of a study group of attorneys, appraisers, and land trust representatives that will attempt to write a set of uniform standards for easement apraisals. The National Trust for Historic Preservation said last month that it was drawing up a checklist of guidelines that could be used by appraisers, easement donors and interested nonprofit organizations.

Another suggested approach to dealing with the appraisal question would be to establish a so-called "safe harbor" provision that would set one minimum percentage figure for the value of all easements. If a taxpayer were willing to accept that amount, no appraisal of the property would be necessary.

"Ten percent is a generally accepted figure for the diminution in value for a residence," said Frannie Goldman, development director of the L'Enfant Trust, one of the three Washington groups that accept historic buildings easement donations. "That would be particularly good for individual home owners who just want to see their homes protected in the future."

So far, only a small number of groups and individuals have commented on the proposed IRS regulations, but many of the informal, verbal remarks the agency has received have been favorable, IRS representatives said earlier this week. Comments on the proposals will be accepted until July 22.