The Nature Conservancy, in the hope of saving some special types of land now almost wiped out by development, has begun the largest series of land purchases by a private group in the history of the conservation movement.

The group plans to raise $30 million to buy and preserve representative types of lands -- including Texas blackland prairie and Southeastern coastal forest -- which are both unique and near to being lost permanently.

To carry out the ambitious project, the Nature Conservancy has had to build a list of the 50 or so bits of land in 21 states that are the most threatened, and are also the most worth saving.

One example of a place to be saved is called Nags Head Woods in North Carolina. About a quarter mile from the ocean on the Outer Banks there are a series of high dunes -- up to 150 feet high with sheer drops into miniature valleys. In these rifts between tall dunes are a series of fresh-water ponds hidden from the killing salt air by the tree-topped first rank of dunes.

The trees and plants here, oddly, are varieties usually found in the mountains -- such as beech, hickory, and red oak -- and not found within many miles of this spot. "In addition, all 35 kinds of trees in the whole Nags Head area, and 70 percent of all the plants -- and most of them the best examples of their kind in the area -- can be found in a little 300-acre patch here. It's a little library of the Outer Banks life," said Thomas Massengale, director of the North Carolina office of Nature Conservancy.

Some 50 such unique sites around the country are expected to be saved. They include such ecotypes as: the juniper-oak savannah in central Texas; the Ceniza scrub in the Rio Grande Valley; bluestem-sacajuista prairie in coastal Texas; mesquite forests in Arizona; tule marshes in California's Central Valley; Central Valley bunch grass areas; vernal pools in the Central Valley foothills; southern California oak woodlands; southern California chaparral; Columbia River basin grasslands in Washington state; foothills prairies in the Rockies; bluestem tall grass prairies in the Midwest, prairieland in Illinois; the "bigwoods" of basswood maples in Minnesota and Wisconsin; elm-ash forest of the South; blackbelt prairie in the South; bottomland hardwood forests in the South; and others.

The huge conservation buy was begun when the Goodhill Foundation of New York offered to donate $10 million if the Conservancy could come up with the other $20 million through fund-raising over the next three years.