WASHINGTON -- A high ranking administrator with the U.S. Department of Interior defended the federal government's decision to seize 500 acres of property in Somerset County for construction of the permanent Flight 93 Memorial.

In an exclusive interview, Steve Whitesell, the department's Associate Director for Lands Management and Planning, said the use of eminent domain was necessary to ensure the memorial opens by September 11, 2011. Whitesell said, "We're at the deadline. We need to start proceeding with construction."

The federal government confirms it has begun the process of seizing approximately 500 acres of Somerset County land to begin construction on a 1,400 acre site for the memorial. The amount of money offered to landowners was not disclosed.

The decision to use eminent domain has triggered controversy among those involved in the planning. Two members of the Flight 93 Memorial Advisory Committee resigned their positions in protest. Pennsylvania members of Congress, including Rep. Bill Shuster, Rep. John Murtha, Sen. Arlen Specter and Sen. Bob Casey, have submitted a letter to the Interior Department:

"We urge you to do everything in your power to reach an amicable agreement with all property owners with whom negotiations are occuring to acquire land necessary for the Flight 93 National Memorial. If no such agreement is reached, we fully expect the NPS and the Department of Justice to pay at least fair market value for the land."

Affected landowners, including Randy Musser of Somerset County, said the timing of the Interior Department's May 7 decision came as a surprise. Though the Interior Department said landowners and government officials were aware of a May 2009 deadline to end negotiations over property, Musser said he wasn't told about such a deadline beforehand.

Whitesell said the U.S. Department of Justice is processing the paperwork to seize the land. He said it'll likely be completed by September. Government contractors are appraising the value of the land to be seized, said Whitesell.