"The park service has no need for the continued use of the building," said park spokeswoman Katie Lawhon. "Its retention is in conflict with the overall goals of the park."
Completed in 1962, the Cyclorama building was designed by the architect Richard Neutra as part of a federal effort begun under President Dwight D. Eisenhower to build visitor facilities at national parks.
The circular structure was built to house artist Paul Philippoteaux's 377-foot-long painting-in-the-round depicting Pickett's Charge, the bloody conclusion of the conflict.
After a multimillion-dollar restoration, the painting was moved in 2008 into the park's new visitor center. The Cyclorama building was left vacant and has been steadily deteriorating.
When the park service announced it was moving forward with plans to demolish the structure, the Recent Past Preservation Network and Dion Neutra, the architect's son, sued, claiming the federal agency had not completed a thorough analysis of alternatives.
In 2010, a federal judge ruled for the group and ordered the park service to conduct a comprehensive review of possibilities for the structure.
In its 200-page analysis released late last week, the park service said it considered an array of factors and three possible alternatives: mothball the building, move it, or demolish it.
The report's final recommendation was to tear it down.
"Demolition best meets the park objectives of protecting and preserving cultural and natural resources by rehabilitating the landscape of the 1863 battle at Gettysburg and its veteran-designed commemoration," the report said.
In recent years the park has embarked on an aggressive effort to restore the battlefield to its Civil War-era appearance, tearing down buildings built on park property, replanting trees, and restoring historic roads and fencing.
Park service officials and others want to remove the Cyclorama building to restore the battle line along Cemetery Ridge, where Union soldiers held off the attack by Confederate Gen. George E. Pickett on July 3, 1863.
Lawhon said it would cost the park $3.4 million to demolish the building compared with $44 million to move it off-site or $1.8 million to leave it where it is and stabilize it until a decision is made at some future date.
The Recent Past Preservation Network said it would file a response during the 30-day comment period and is weighing other options.
"We continue to be disappointed that the Cyclorama is vehemently defended and characterized in all alternatives as a modern intrusion rather than a memorial - a monument to the conflict and to unity," said Alan Higgins, president of the Recent Past Preservation Network, "and that the agenda to destroy an element of the collective and dynamic cultural landscape at Gettysburg remains at the forefront, with the Cyclorama unsympathetically isolated as an inconsequential feature."
Dion Neutra, 85, said he did not understand why the park service would target his father's building when the landscape itself has evolved so radically over time, beginning with the installation of hundreds of monuments honoring units that fought there and later motels and other buildings to serve the hundreds of thousands of tourists who visit each year.
Neutra wants to see building preserved and turned into a museum honoring Abraham Lincoln, as his father once envisioned.
Lincoln delivered his Gettysburg Address only a few hundred yards away in November 1863, just four months after the battle.
"Our building now is part of the history of the battlefield and worthy of preservation as part of a continuum," he said. "People could honor Lincoln by going there to cogitate on what the Great Emancipator said then, which is still relevant today."
Contact Amy Worden at 717-783-2584 or firstname.lastname@example.org or follow @inkyamy on Twitter.