Plans for a Sept. 11, 2001, memorial at the Flight 93 crash site in Southwestern Pennsylvania got a significant boost yesterday when the federal government reached agreements with at least half of the people who collectively own the last 500 acres needed.

The Department of the Interior warned the owners last week that their properties would be seized by eminent domain if no deal was reached by yesterday's deadline. Although the talks have at times been contentious, by day's end it was clear that negotiations would continue with the owners who were still holding out.

"We're working to finalize agreement-in-principle with a number of landowners," said Kendra Barkoff, spokeswoman for Interior Secretary Ken Salazar.

Barkoff said a more definitive announcement was expected in coming days. She declined to provide details, but three of the six landowners confirmed that they had reached sale agreements.

Dan Wenk, acting director of the National Park Service, who negotiated with the landowners, said that remarkable progress was made this week and that he would work through the weekend to reach agreements with the holdouts.

For those who reached deals, it was a burden lifted after many years of on-again, off-again talks with the Park Service, which has been trying to assemble 2,200 acres in a remote section of the Allegheny Mountains for the memorial park.

"We've negotiated and come to an agreement," said Linda Musser, who with her husband, Randall, owns a 2.83-acre parcel that will be used as right-of-way near the edge of the park. "We're glad it's over."

Landowner Tim Lambert said that parting with land that had been in his family since the 1930s was difficult but that he had been willing to do it since 9/11, when the fireball from Flight 93 scorched the evergreens at his property line.

"I'm relieved," said Lambert, who reached a "handshake deal" with the government on 163 acres, including a six-acre parcel that he will donate to the park.

"In less than a week, we reached middle ground," he said. "I'm glad it will let the memorial process move forward."

Property owner Christine Williams told the Associated Press that she was waiting to sign paperwork and called the deal favorable.

None of the property owners would disclose the terms of sale of their lands, which in some cases include natural gas, coal, and timber rights.

The threat of eminent domain, first announced by federal officials in early May, angered property owners and residents of the Somerset County community of Shanksville, whose rural lifestyle was upended by the national disaster.

"It really put a damper on things," Musser said of the threat. "It was upsetting to all of us."

A spokeswoman for the Families of Flight 93 said the relatives of the 40 passengers and crew who died in the crash welcomed yesterday's news. "We are optimistic about reaching our goal of the dedication of a substantial permanent memorial by the 10th anniversary of the events of Sept. 11," Lisa Linden said.

A ribbon-cutting for the Flight 93 National Memorial Park, 60 miles southeast of Pittsburgh, is set for Sept. 11, with the first phase of construction slated to begin by November.

Contact staff writer Amy Worden at 717-783-2584 or aworden@phillynews.com.