Perched on crumbling shale in a remote section of Alleghany County, Christopher Clampitt observes a few fragile sprigs of Kate's mountain clover. Along the Potomac, Larry Morse seeks out the fruits and flowers of Steele's meadow-rue, to compare them with a doubtful sighting on the Blue Ridge.

The forays of the two botanists are part of the Virginia Natural Heritage Program, a new, systematic effort to locate and catalogue occurrences of the state's rarer plant and animal species so that they may be preserved. The program was initiated by the Nature Conservancy, a nonprofit organization that is splitting the cost of the $260,000, two-year pilot project with the state.

The new information is expected to serve commercial and environmental interests, said the conservancy's state director, George Fenwick.

A similar fund of data on endangered species might have averted what he calls the "Great Snail Darter Episode." Completion of a $119 million dam on the Little Tennessee River was halted for three years in the late 1970s by the discovery of a three-inch perch that has since become emblematic of environmental conflicts.

"They would have known that the snail darter not only occurred at that particular dam but on several tributaries," he said. "Had there been a heritage program, they could have made an informed decision."

The conservancy's first cataloguing program was launched in South Carolina in 1974. Since then, six Latin American nations and 46 states have adopted some form of it, according to the Nature Conservancy's national headquarters in Arlington. Virginia became the 44th last August.

Michael Lipford, the state program's ecologist and coordinator, said about 600 plants, 585 animals and 40 habitat communities have been noted as worthy of monitoring so far. The major part of the survey to date has been on plants.

Of the plants, 35 have been flagged as exceedingly rare, not only in Virginia but everywhere. Thirteen of those may be recommended for inclusion on the state's list of endangered species.

That list now has only three items: ginseng, the small world begonia and the Virginia round-leaf birch. A fourth species, the Peters Mountain mallow, is a candidate for both federal and state protection. Only six stems are known to exist.

A team of five conservancy employes, under contract to the Virginia Department of Agriculture and Consumer Services, collects information on plants and animals from the Smithsonian Institution, herbaria, museums and collections around the state, undertakes field surveys, and subcontracts other surveys to specialists.

When, say, a chestnut lip-fern is located (its few appearances in Virginia and West Virginia are the only ones east of Texas), 64 items of information about the plant and its surroundings are noted for a computer record, including the ownership of the site and any threats to the plant. Each occurrence is also keyed to a topographical map, but information about the plants' precise locations is protected as vigilantly as the rare species themselves, to prevent them from being "loved to death" by well-meaning visitors.

Lipford said the Virginia program's method of cataloguing the information has become something of a model for other conservancy-sponsored surveys.

So far, about 2,000 plant, animal and habitat types have been logged, and another thousand or so await processing. Each is given a ranking of one to five, based on rarity and other vulnerability factors. A state as well as a "global" ranking is assigned.

Thus, an entry in the burgeoning data bank would tell a highway engineer requesting environmental information on a proposed route that the red-shouldered hawk was last observed in woods near Rte. 50 and Gallows Road, and it is "S3," rare within the state but not immediately threatened. It is also "G5," secure and not meriting special concern throughout the rest of its range, which extends north of Virginia.

By the end of June, Lipford had fielded more than 450 such requests from state agencies and developers.

Information about other natural features is being coded, mapped and typed into the system: lists of caves, significant waterfalls, nesting areas and rattlesnake dens, and trees of "championship" height and girth. A pin cherry near the Rose Lane Motel in Galax is the tallest of its species in the state. An American elm discovered last year along the Nottoway River is the largest in the nation at 125 feet, easily overshadowing a 99-foot Kansas specimen, the former champ.

Lipford stressed that this computerized clump of information is not a static artifact like a list, or a report from a blue-ribbon commission. It will grow or contract, depending on the new information it incorporates. The yellow blooms of a species of "S3" buckwheat have turned up in unexpected numbers this summer, for example, and its ranking may decline.

Lipford cites these reasons for concern about the loss of entire species:Many pharmaceuticals derive from plants and, presumably, others await discovery. A new treatment for childhood leukemia was recently derived from the rosy periwinkle.

"It's the height of ignorance and arrogance to eliminate a species we know nothing about," Lipford said. Some species serve as indicators of environmental quality, like a canary in a coal mine, because they are sensitive to changes that may eventually affect the well-being of humans. There is room for suspicion that if humans cannot fend off threats to biological diversity, they may be the next victims of the narrowing spectrum. "My great-grandfather walked down these roads, and these species were here then. We should protect them for our descendants."

The conservancy's long-term goal is to protect living examples of existing species and habitat communities within each state and in other countries. A short-term goal is to persuade the state General Assembly to vote funds to make the program permanent at its 1988 session.