"The planning process is ongoing and the information contained in the release should not be considered final," Olson said.
President Obama and Congress have until Friday to reach a budget deal. Failure to do so would trigger $85 billion in cuts.
Gettysburg Park would lose nearly 7,000 volunteer hours because of a lapse in volunteer coordinators, according to the memo.
The document also says Gettysburg would be less able to address invasive species, would cut 20 percent from its student education programs, and would cut back a program to remove exotic species.
"We're planning for this to happen and hoping that it doesn't," said Park Service spokesman Jeffrey Olson, who confirmed that the list represented cuts the department was considering.
Park Service Director John Jarvis asked superintendents last month to show by Feb. 11 how they would absorb the 5 percent funding cuts. The memo includes some of those decisions.
Though not all of the nation's 398 parks had submitted plans by the time the memo was written, a pattern of deep slashes that could harm resources and provide less protection for visitors has emerged.
In Yosemite National Park in California, for example, park administrators fear less-frequent trash pickup could attract bears into campgrounds.
The memo says that in anticipation of the cuts, a hiring freeze was in effect, and furloughing of permanent staff was on the table.
"Clear patterns are starting to emerge," the memo said. "In general, parks have very limited financial flexibility to respond to a 5 percent cut in operations."
Most of the Park Service's $2.9 billion budget is for permanent spending, such as staff salaries, fuel, utilities, and rent payments. Superintendents can use about 10 percent of their budgets on discretionary spending for items ranging from interpretive programs to historic-artifact maintenance to trail repair, and they would lose half of that to the cuts.
"There's no fat left to trim in the Park Service budget," said John Garder of the National Park Conservation Association, a nonprofit advocacy group.
For years, Congress has been cutting funding to the Park Service, and in today's dollars it is operating with 15 percent less than a decade ago, said Garder, the nonprofit's budget and appropriations legislative representative in Washington.
Inquirer staff writer Alfred Lubrano contributed to this article, which also contains information from the Associated Press.