WASHINGTON (AP) _ Pathologists working at a military mortuary at Dover Air Force Base, Delaware, have succeeded in identifying all 248 soldiers killed in a Dec. 12 airplane crash at Gander, Newfoundland, Pentagon sources said Monday.

The sources, who asked not to be identified, said the Defense Department was planning to announce the successful end to the 2 1/2 -month identification process on Tuesday afternoon.

The sources added the identifications actually were completed last Saturday, but a strict lid of secrecy was placed on that information while the Army contacted relatives of the victims.

One source told the Associated Press the key to completing the identification s was the work of a special Army team that returned to Gander last month and spent almost four weeks sifting the crash site for addditional evidence.

''It was the additional evidence and remains that they found in combing the site inch by inch that finally allowed them to finish,'' the source said. ''Somehow they actually got an ID on every victim.''

Besides identifying the 248 soldiers killed in the crash, the source continued, the pathologists also identified all eight crew members.

The victims died when a chartered Arrow Air DC-8 crashed shortly after taking off from a refueling stop at Gander. The jetliner was carrying members of the 101st Airborne Division back to Fort Campbell, Kentucky, after six months of Mideast peackeeping duty in the Sinai Desert.

The cause of the crash is still under investigation by Canadian and U.S. officials.

From the start, Army officials predicted it could take months to identify all the victims. While the pathologists were initially hampered by a lack of personal medical records on the victims, their biggest problem involved the severity of the crash impact on the bodies. The fuel laden jetliner exploded upon impact with the ground.

But one source said the patholgists were able to recover enough remains from each individual to make the positive identifications.

The successful identifications will allow the Army to avoid the need for a mass burial. Just last month, when almost half of the victims were still unidentified, the Army had said it might not ever be able to identify some of the soldiers.

One source said the Army was now in the process of working out final burial arrangements with each family and the victims would be moved out of Dover over the next two or three days for burial.