WHATEVER OTHER legacies Parris Glendening may leave Maryland, the preservation of unspoiled lands for public use will be the most treasured. Gov. Glendening has made Maryland a leading state in studying the high costs of ill-considered growth and finding opportune investments in open spaces. This month he is negotiating what would be the largest-ever single land deal -- for about 58,000 forested acres on the Eastern Shore. Part of a three-state arrangement to protect Delmarva, the latest acquisitions would be the "crown jewel" in his land-use program, the governor says.

Virginia and Delaware plan to purchase another 9,000 acres each, for a three-state total of 76,000 acres in parcels up and down the peninsula. Maryland is to buy about half the 58,000 acres and to receive the other half as a gift from the Richard King Mellon Foundation, after the foundation has come up with plans for a sustainable forestry operation.

The Delmarva acreage is being made available by the Chesapeake Forest Products Co., owned by the Chesapeake Corp. of Richmond. The company announced earlier this year that it was getting out of the timber business and planned to sell much of its land to John Hancock Mutual Life Insurance Co. Hancock approached the nonprofit Conservation Fund, a trustee for the Mellon Foundation.

The land involved is a series of forests covering watersheds that feed the bay and nearby waterways. The acreage stretches across five Maryland shore counties, fronting five rivers. Many of the tracts have been voluntarily set aside by Chesapeake for the protection of wildlife and water quality.

Last year Maryland decided to buy Deep Creek Lake, in the mountains of Garrett County, to preserve land as well as to ensure that current property owners could retain access to the utility-company-owned lake. Other public acquisition plans included the Chapman's Landing acreage along the Potomac in Charles County, where a housing development had been planned. On a smaller scale, the state -- along with Montgomery County and the federal government -- has worked on a proposal to rebuild Glen Echo Park.

Governments shouldn't be gobbling up land all over the place merely to stop growth or to stockpile ordinary terrain. But when reasonable prices can be negotiated to preserve public access, to save valuable wetlands and to protect wildlife, the benefits to future generations can be priceless.