The FBI has been called in to investigate the New Year's Eve theft from the National Portrait Gallery of four handwritten notes signed by President Abraham Lincoln and three of his most famous Civil War generals.

Security officers at the gallery said the incident, which gallery officials have called unusual and perhaps unprecedented, has been turned over to the bureau and D.C. police, who reported no new leads yesterday.

The notes were taken sometime Monday afternoon from a railing-mounted display case overlooking a stairway at the east end of the Portrait Gallery, where an 18-foot-wide painting of "Grant and His Generals" is displayed.

The note signed by Lincoln is actually an Army pass dated Sept. 23, 1864, introducing the painting's artist, Ole Peter Hansen Balling, to Gen. Ulysses S. Grant, during the siege of Richmond in 1865.

The other notes, signed by Grant, Gen. George G. Meade and Gen. George Armstrong Custer, the flamboyant officer later killed by the Sioux at Little Bighorn, were 1866 appreciations by the generals of Balling's portrayal of them galloping on horseback with two dozen other Union military leaders.

Suzanne Jenkins, the Portrait Gallery registrar, said the documents were given to the gallery with Balling's painting in the mid-1960s and had been on display for about eight years.

They were bolted into a wooden frame beneath a sheet of plexiglass that the thief apparently pried loose, Jenkins said. She said the theft was discovered about an hour before the gallery's 5:30 p.m. closing on a day when visitation was lighter than normal because of the absence of school groups.

Balling, a Norwegian artist who sketched Lincoln in the White House in the fall of 1864, spent five weeks with Grant sketching officers in the field but never saw all his subjects assembled. The painting was completed after the war.

The notes from the generals, which Jenkins said were written on lined paper apparently from some sort of ledger, may have been comments written at their first viewing of the painting, Jenkins said.

Though police placed a preliminary estimated value of $90,000 on the missing documents, Jenkins and Allen Fern, the gallery's director, said they had no way of confirming that estimate yesterday without consulting autograph dealers, and thought it was probably far too high.

They said the documents, while a valuable and interesting adjunct to the Balling painting, were not the sort of artifact the Portrait Gallery would ordinarily seek out and purchase and certainly not for $90,000.

'We are, after all, a portrait gallery," said Fern. "There are other priorities."