The museum would rise on 78 of those acres, on a hillside that offers sweeping views of the Schuylkill and Valley Forge National Historical Park. If all goes according to plan, construction would start by the summer of 2008. Talk about a museum began in 1995.
The center will house more than 15,000 rare documents, artifacts, weapons and other materials, many of which have never been publicly displayed.
"The time for a center to commemorate the American Revolution and the independence of our nation is long overdue," said H.F. "Gerry" Lenfest, chairman of the board of the American Revolution Center (ARC). "Now we have the opportunity to make it a reality."
The Lenfest Foundation is contributing $3.1 million toward the purchase of the land. The state and county are each contributing $2 million from open-space funds.
The county has also pledged $2.5 million and the state $20 million toward the estimated $60 million to $70 million construction costs. The entire campaign is pegged at $150 million, including a $40 million endowment.
The project's backers believe that fund-raising should not be a problem. "We feel something of such great national importance can get support nationally," said Lenfest.
Lenfest and other ARC officials are expected to unveil details of the project tomorrow at a meeting of the Montgomery County commissioners before they approve the expenditure for the county's share.
"This property has been high on our priority list for open space," said Commissioners Chairman Tom Ellis. "It just made a lot of sense for us. We think this will make Montgomery County a destination site."
The ground borders the Schuylkill, the Perkiomen Trail, the Schuylkill River Trail, and the Mill Grove preserve, he said.
Gov. Rendell, who at one point offered to buy back Valley Forge from the federal government after it blocked plans for the museum, called the purchase "a good development in a great location."
"Doing this will not only help us build the center but also preserve open space, which is extremely challenging in Montgomery County," he said. "It's a very positive step."
The combination of Independence Mall and the National Constitution Center, the ARC museum and Valley Forge, and Gettysburg National Historical Park makes the state a premier destination for heritage tourism, he said. "Not even Massachusetts can come close," Rendell said.
Archdiocese spokesman Matthew Gambino said in a statement that the land for this project was not critical to the mission of St. Gabriel's Hall, which serves delinquent boys from Philadelphia and surrounding communities.
"Catholic Social Services of the archdiocese, which oversees St. Gabriel's, tried to be sensitive to its own operational needs and the needs of our Audubon neighbors as it sought a partner for the sale of the parcel," Gambino said. "Proceeds will help St. Gabriel's continue its century-long mission."
Lower Providence Township Manager Joe Dunbar said that, under the current zoning, hundreds of houses could be built on the land.
"It's a creative way to preserve open space, negate another 300 houses, create jobs, and preserve history," he said of the project.
The price for this ground is far less than the $8.5 million the federal government paid Toll Bros. Inc. in 2004 for 62 acres to keep luxury homes from sprouting inside the park's boundaries.
But that close call triggered the interest of the Conservation Fund, a nonprofit organization based in Arlington, Va., which steps in when critically important environments are at risk of being developed.
The fund had the archdiocese land under contract when this deal came along, said Blaine Phillips, the fund's mid-Atlantic director. The fund was happy to yield, he said.
"We acted as an agent to make sure the property was protected," he said. "We were there at the right time. We took the first step."
When plans for the museum were unveiled three years ago, it was designed to be built into the side of a cliff along the edge of the lower parking lot at the Welcome Center of Valley Forge National Historical Park.
The architect, Robert A.M. Stern, said 80 percent of that design can be transferred to the new site, with the added bonus that it can be built without blasting through rock.
The property the ARC is acquiring is within the congressional boundary of the park, but it is not owned by the National Park Service, a crucial distinction, said Lenfest.
One reason the partnership between the center and the National Park Service dissolved in 2005, Lenfest said, was the restrictions the agency places on fund-raising, construction, and operations. Now, those issues will not be an obstacle, he said.
"Their interests were to protect the United States taxpayers," he said. "We couldn't live with the restrictions."
That doesn't mean, however, an end to a cooperative relationship with the park, said center and park officials.
"We believe that the American Revolution is a huge story and that there is much to be told," said Valley Forge park superintendent Mike Caldwell. "The more ways to tell the story, the better."
About the only sour note to be heard about the deal came from Bruce Baky, president of the Friends of Valley Forge, who worries that there was too much geographical separation - including the Schuylkill - between the park and the museum for both parties to benefit.
"We're decidedly ambivalent about the value of what they are doing," Baky said. "I don't think it's going to get us where we need to go to tell the story of the American Revolution."
Contact staff writer Nancy Petersen at 610-701-7602 or firstname.lastname@example.org.