For years, the historic, 1,000-acre Mount Airy plantation in Rosaryville has been more of a burden than a boon to the state.

It became a 1,000-acre state park in the 1970s but has no facilities for the public. Two attempts beginning in 1985 to turn the manor house into an elegant restaurant and inn ended in failure, bankruptcy and labor disputes. For most of this decade, its gates have been kept locked, and its future was uncertain.

But now, the estate eight miles south of Upper Marlboro has a new lease on life, under a plan approved recently by the Maryland Board of Public Works. For at least the next 15 years, a small group of residents known as the Rosaryville Conservancy will oversee the property, holding equestrian events there while making the entire park more accessible to the general public.

The manor house, part of which was built in 1665 as a hunting lodge for the third Lord Baltimore, proprietor of the Maryland colony, will be rented out for weddings and other special events, under the management of Pineapple Alley Catering, a Clinton company that will have exclusive rights to prepare the food.

"We have since the early '90s been trying to figure out a way to have something happen there from the private sector," said John Surrick, spokesman for the Maryland Department of Natural Resources. "From the state's perspective, what we're hoping to gain is money for regular maintenance and upkeep and management. Our goal is to have it up and running at a minimal cost to taxpayers."

Until now, taxpayers have lost money on the place, which has been largely inaccessible to the public in part because the state lacked funds to develop the park. The failed attempts to develop its manor house as a restaurant and inn, from December 1985 to November 1991, were costly.

In the process of failing, the restaurant operators stopped making payments on $675,000 in state enterprise loans backed by Prince George's County, employees walked off the job when their checks bounced, and the state canceled the lease. The first firm that ran the restaurant said it spent $2 million to renovate the property, and the state invested an additional $1 million in the property, according to Surrick.

Since the restaurant closed, the manor house had deteriorated. Now, as the house is readied for this summer's planned reopening under Pineapple Alley, the state is plowing $240,000 more into repairing its roof, plumbing, heating and air conditioning.

Through it all, the handful of members of the Rosaryville Conservancy has mowed the fields and trimmed the trails elsewhere on the estate and has sponsored equestrian events at the site. Such programs will continue under the new agreement.

The conservancy hopes also to turn a tobacco barn on the property into a museum, begin interpretive nature programs, and better market the park's pavilions for family reunions and other uses.

"We plan on having it open to everybody so people can access and enjoy it," said Sally Marshall, whose home and horse stable adjoin the property. "Now, you have to be an insider, someone who knows the park and who to contact."

The manor house has a colorful history that includes visits by five U.S. presidents. The first member of Maryland's founding clan to live there was Benedict Calvert, who took up residence in 1760. George Washington was a frequent visitor, and Mount Airy was the site of the 1774 wedding of his stepson, John Parke Custis, to Eleanor Calvert. The property remained in the family until 1902, when it was sold at auction.

In 1931, it was purchased by Eleanor Medill "Cissy" Patterson, publisher of the old Washington Times-Herald, and used as one of her country estates until her death in 1948. She bequeathed the property to a friend, Ann Bowie Smith, who was a Calvert descendant. Legislation to turn the property into a state park was approved in 1970, and the land was acquired in 1973.

"We used that land for fox-hunting for years for the Marlboro Hunt," said Edward L. Coffren III, former hunt master and president of the conservancy, which he formed in 1991. "I was farming the land in the '70s and '80s, keeping it mowed, renting the land from the state, and raising corn and soybeans. We were trying to preserve it and keep it in open space, so I formed the conservancy with four or five people."

Coffren said his group had hoped the restaurant would provide the cash to properly maintain the park and expand its use, and that's still the hope for the facility. Under the new agreement, Pineapple Alley will turn 90 percent of the rental income over to the conservancy exclusively for Rosaryville State Park.

Chef Tom Mueller said he is projecting $109,500 in rental revenue the first year. He said the rental fee on weekends will be $2,400 for eight hours, compared with $2,880 at Newton White Mansion and $2,520 to $2,880 at Oxon Hill Manor, two other historic properties. Newton White and Oxon Hill, unlike Mount Airy, are owned and operated by the county and used for weddings, corporate receptions and political events.

"We won't be doing a restaurant, but we'll do a lot for the public," said Nancy Goodier, Mueller's partner. "We're going to have an archaeological dig, and we plan to restore the gardens to what they might have been in the 1700s. The house has a marvelous history. The more we can find out, the better."

CAPTION: Tom Mueller and Nancy Goodier, of Pineapple Alley Catering, and Dorothy Troutman, of the Rosaryville Conservancy, talk in the doorway of the historic Mount Airy manor house.

CAPTION: The manor house, begun in 1665, has had a colorful history, including visits from five presidents.