Marshall Hall, an 18th-century plantation mansion overlooking the Potomac River, is just a burned-out shell now. Its four charred and crumbling brick walls house rotted wood and bits of peeling whitewash, but there are no ceilings, floors or windows.

This is the house of Peggy Marshall's dreams.

Marshall, a descendant of the Colonial Maryland family that built the Charles County mansion about 1730, will devote the next 25 years of her life, if that's what it takes, to getting the National Park Service, which now owns Marshall Hall, to rebuild her "baby" and turn it into a visitors center. And Marshall is not the only one transfixed by the ruin and its history.

Also under the spell of Marshall Hall--which sits in Piscataway National Park just across the Potomac from Mount Vernon--is ranger Don Steiner, who cried the October 1981 day the house was devastated by a still-unsolved arson.

Clinton Addison, whose family managed a popular amusement park on the grounds for decades, is similarly bewitched. Addison, 38, of Waldorf, is so devoted to the idea of bringing Marshall Hall back to life that he makes regular trips out to the remote site to look after what's left of the house. He often replays the fateful fire in his mind, wishing desperately that he could have been there to put out the blaze.

All three chastise the Park Service for neglecting the historic property and for not rebuilding the house.

Marshall, 47, of Fairfax, hopes to raise millions of dollars to do what the Park Service once promised to do. A seismic researcher at the Defense Department, she recently cut back to a part-time work schedule to accommodate her campaign. Marshall is in the process of setting up a nonprofit foundation, and she will begin studying for a master's degree in historic preservation at the University of Maryland in the fall.

But Marshall may have an uphill battle attracting a wider audience for Marshall Hall. Over the years, supporters have come mostly from the ranks of people who visited or worked at the amusement park there or who have Marshall blood. Like many historic sites, the plantation house has no single selling point, no angle--no famous person or epic story.

"We'd like to restore Marshall Hall, but not enough people are interested in it. It's way down in the country," said Gary Scott, a Park Service historian. "Marshall Hall just has not been that much of a public interest, and the Park Service always has other priorities. I don't see national visitors from Washington, D.C., going out there."

The government's point of view used to be different. The Park Service spent about $5 million to purchase Marshall Hall in 1974. The house and grounds were added to Piscataway Park, largely in a bid to preserve the view from Mount Vernon, according to Scott. Even several years after the mysterious fire, park officials promised to restore Marshall Hall and use it as a visitors center.

But now, the Park Service has reversed itself, saying that Marshall Hall is "considered a ruin" that does not conform to its standards "as a property suitable for rehabilitation."

Peggy Marshall is incensed. She and Addison hold the Park Service responsible for the fire because the mansion had no overnight ranger or other security. Marshall said the plantation house continues to go neglected. Its walls were reinforced after the fire, and a new stabilization effort is planned for this year. However, she fears that Marshall Hall's three chimneys--which now bend precariously at an angle--could collapse any day.

"It is very obvious to me that they want it to fall down, and the sooner the better, as far as they are concerned," Marshall said.

She sees politics in the marginalization of Marshall Hall. High-profile support can make or break a historical project, and this one has yet to win a powerful champion.

She notes other Washington area sites that recently have been rejuvenated by having a political benefactor. Montgomery County Executive Douglas M. Duncan (D) won a pledge of $6 million from the state for Glen Echo Park in the spring, while Rep. Steny H. Hoyer (D-Md.) pushed the appropriation of more than $1 million from Congress last year for the Sotterly Plantation on the Patuxent River in St. Mary's County.

Marshall believes that she can sidestep the National Park Service and get financial support from private sources or with the help of politicians who take up her cause. At the very least, she wants to see the house rebuilt as a sound structure with a roof and windows. She's still formulating the missing angle.

Maybe it could become a museum of the Marshall family or, she muses, of the Potomac River in concert with the Potomac American Heritage River project. She believes there is a large hidden audience for her project, citing the e-mail she receives each week from several visitors to the Marshall Hall Web site--mostly wistful memories of the amusement park.

Marshall Hall was built about 1730 by Thomas Marshall, the older brother of Peggy Marshall's seventh great-grandfather. The plantation primarily grew tobacco, and it used slave labor into the 1850s. Thomas Marshall II was a member of the Committee of Correspondence for Charles County, according to Peggy Marshall's research, and corresponded with George Washington about a possible land-swap that never went through. His son, Thomas Marshall III, was twice a guest of Washington's at Mount Vernon.

About 1900, Marshall Hall became an amusement park that hosted jousting tournaments and other cultural events. Many Washingtonians still fondly remember family trips to the park, with its swimming pool and rickety roller coaster. Or they recollect the seedier side of its later years--the Happyland slot machines, the drunken fights and the tensions that accompanied its integration in the 1960s.

Today, a visitor to Marshall Hall finds a dilapidated cemetery, a half-mowed lawn, picnic tables, an insecure fence around the house and a portable toilet that apparently hasn't been pumped in a year.

"We have beautiful resources here; why can't we do more with them?" park ranger Steiner lamented. "This is an important site, and to totally ignore it is wrong."

But will Marshall Hall ever generate enough interest for these devotees to realize their dream? "That's the big question with all of these properties," said Kay Volman, president of the Charles County Historical Trust. "They can't all be saved, because someone has to maintain them."

According to Scott, the Park Service historian, Marshall Hall is most valuable for its early architecture. The largest house in Southern Maryland built before 1740, it has a vernacular English look, Scott said, unlike many 18th-century Georgian plantation houses. "It's one of the earliest things we've got," he said.

Despite their overflowing zeal, Marshall Hall's partisans have trouble describing exactly what its appeal is, beyond age. "It's the family that lived there and the human relationships," Marshall said. For Steiner, "it's calm beauty" that makes the place special, as well as the delight of returning visitors who grew up with the amusement park. "Just watching their faces is a reward," he said.

Marshall knows that the rest of the world may need some convincing, but she says that failure is inconceivable.

"I'm not going to tolerate it not being taken care of," she said.