Strapped into the jumpseat of a National Guard helicopter, Gov. Parris N. Glendening today surveyed a portion of the 58,000 acres of Eastern Shore forest that he wants to acquire for preservation, hoping to show off the merits of his planned purchase.

A carpet of green treetops spread out beneath the whirring blades of the Blackhawk as far as the eye could see, interrupted here and there by a muddy river snaking through the landscape or the linear lines of farmland, carefully cut into squares and rectangles.

When a small subdivision of houses popped into view, Glendening (D) spotted the justification he was seeking for making the largest land purchase in state history.

"Think about development along the Potomac River and the Patuxent and several rivers in the Baltimore area," Glendening told reporters later. "Then think about what you see here and know that if we do not move aggressively, then in another 20 to 25 years . . . we can see the same type of growth and development along these rivers. And once it's lost, that will never be recaptured."

Glendening has proposed that the state preserve 58,000 acres scattered across five Eastern Shore counties by splitting the $33 million cost with the Richard King Mellon Foundation, a private charitable organization. Each would spend $16.5 million to buy 29,000 acres, and the foundation eventually would turn its parcels over to the state to manage.

Maryland would buy the land from the Chesapeake Forest Products Co., which is selling its timber business. Never has the state bought so much land at once. Since 1969, the state has purchased 189,000 acres as part of its Program Open Space.

Glendening, who also toured the area yesterday by boat on the Nanticoke River and Marshyhope Creek, talked to reporters at a Boy Scout camp in Dorchester County. Behind him, wild rice and pickerelweed swayed in the breeze. A tangle of sweet gums and maples stuck out of the banks like toothpicks in a tray of cheese cubes.

"It is not until you see firsthand what is really at stake here that you appreciate . . . the decisions that have been made," Glendening said.

The pending acquisition of the Eastern Shore properties is part of a Glendening initiative to use tax dollars to buy open land to save it from development. It also ties into his smart growth efforts to discourage new development in rural areas such as the Eastern Shore.

Glendening said the state will use money from its reserves to buy its portion of the land.

The Board of Public Works, which overseas state purchases, tentatively approved the deal but with conditions. Mike Morrill, a spokesman for the governor, said that in recent days all of those conditions were met, including a stipulation that the land be appraised at a value greater or equal to the purchase price.

The negotiations, which are being brokered by the Conservation Fund, a national nonprofit, could be completed by early September, several weeks later than expected. State officials attributed the delay to the amount of work involved in researching 673 different land titles that comprise the purchase area.

The deal also hinges on approval of land sales in Virginia and Delaware, as Chesapeake Forest Products, owned by Chesapeake Corp. of Richmond, sells off most of its nearly 280,000 acres in the mid-Atlantic region to the John Hancock Mutual Life Insurance Co., which has a timber subsidiary.

The governor and conservation officials credited Hancock for approaching the state with its offer to sell the land for preservation.

Brent Keefer, southern region planner for the Hancock Timber Resource Group, said the Eastern Shore land is particularly sensitive because of its dual characteristic as wetlands and forest.

"That led us to think about alternatives here," he said.

Conservationists said the deal is a protection against the future. While the land is still extremely valuable for the hardwood and pine it produces--and some timber will continue to be harvested--eventually the forest will decrease in value. Once that happens, a private company probably could make more money selling the land for residential and commercial development.

William C. Baker, president of the Chesapeake Bay Foundation, said that scenario would be harmful to the health of the critical watersheds in the five-county area that includes Wicomico, Dorchester, Worcester, Somerset and Caroline counties.

"Sprawl is killing the Chesapeake Bay," he said, adding, "There [are] certain acres that are so important that they should never be developed."