Officials in Gettysburg are hoping to borrow one of the nation's most historic documents — an original copy of Lincoln's Gettysburg Address.The foundation that runs Gettysburg National Military Park's museum and visitor center wants to borrow a copy held by the Library of Congress and put it on public display as part of its celebration of the 150th anniversary of Lincoln's famed speech. Pennsylvania Sen. Robert Casey wrote to the library Tuesday expressing his support of the plan.But Gettysburg might have to look elsewhere. The library does not lend either of its two copies of the speech because of their fragility and priceless nature.The library owns two of five known copies written in Lincoln's hand. Another copy is on display in the Lincoln Bedroom of the White House. The other copies are held by Cornell University and Lincoln's presidential library in Springfield, Ill.The library's versions include what is known as the Nicolay Copy — the earliest draft of the speech and the one that Lincoln may have read from — and the Hay Copy, thought by many scholars to have been written by Lincoln shortly after he returned to Washington. The library obtained both copies from the surviving children of Lincoln secretary John Hay in 1916.A 1990 policy precludes the library from lending its most important documents, including the Gettysburg Address and Thomas Jefferson's rough draft of the Declaration of Independence, library spokeswoman Gayle Osterberg said."This was done because of our serious concerns about protecting such fragile, priceless, and irreplaceable documents," Osterberg said via email.Additionally, she said, the Hay family's preference is to keep the documents where they are.Given the coming anniversary, Casey wants the Library of Congress to make an exception."It is my understanding that the museum and visitor center can provide the required and appropriate security, climate control, lighting levels and curatorial oversight through National Park Service professionals that would be required to handle such a historic document," he wrote Librarian of Congress James Hadley Billington.Lincoln delivered the immortal words of the Gettysburg Address — "Four score and seven years ago ..." — at a dedication of the Soldiers' National Cemetery on Nov. 19, 1863, more than four months after the Civil War's pivotal battle.A number of events are planned to mark the anniversary. President Barack Obama has been invited to the main anniversary ceremony in Gettysburg on Nov. 19.