Only about 5 percent of land in the continental U.S. is developed. But that reality hasn't stopped extreme environmentalists -- as well as politicians who want to appear pro-environment -- from raising fears that America is losing wilderness and farmlands.

Some events in Pennsylvania illustrate how relying on faulty data can prompt the kind of panic that gives birth to wrong-headed land use policies.

• In a study called the National Resource Inventory, the U.S. Department of Agriculture calculated that Pennsylvania lost 1.1 million acres to development in 1992-1997 -- or about five times the land "lost" in 1982-1992.

• Then the USDA withdrew the inventory in April, citing a computer programming error -- but not before Pennsylvania policy makers had swung into high gear.

Using the flawed data, Pennsylvania bureaucrats promoted legislation and land use plans called "Growing Greener" and "Growing Smarter" which include buying land to preserve open space and giving towns incentives to follow "smart growth" policies.

The bureaucrats say they have no plans to correct the land use report that was based on the USDA's faulty figures. However:

• Steven Hayward of the Pacific Research Institute calculated that for the USDA's figures to be accurate, Pennsylvania would have had to develop 28 acres for each new resident in the state.

• He and Heritage Foundation economist Ron Utt looked at data on the number of new homes in the state and the number of farms -- and concluded that only about 22,000 acres of farmland had been lost.

Source: John Berlau, "Is Farmland Vanishing? Not Exactly, Data Show," Investor's Business Daily, July 21, 2000.