The five Moslem militants condemned to death for the assassination of Anwar Sadat last October were executed at dawn here today only a few hours after their final plea for mercy was turned down.

Late last night, President Hosni Mubarak rejected the request for clemency from the five, clearing the way for their execution.

Lawyers for the convicted men said the two active military officers, Lt. Khalid Ahmed Shawki Islambouli, 24, and Sgt. Hussein Abbas Mohammed, 28, were killed by a firing squad, and the other three, all civilians, were hanged.

Most Egyptians first learned of the executions in midmorning from other Arab and Western radio broadcasts. Apparently fearing public protest to the executions, the government waited several hours before announcing them.

First word came in a brief news item carried over Cairo radio in the early afternoon. The official Middle East News Agency waited nearly 12 hours before mentioning the executions. There were no reports of disturbances.

Abdel Halim Ramada, the chief defense lawyer, told reporters that families of the five executed men had not been allowed to witness their execution or be given their bodies, which were buried in unmarked graves in an unknown cemetery.

The families, he said, were not accepting condolences, "only congratulations, because they consider their sons martyrs revered in the eyes of God."