CAIRO — Just days before the final round of Egypt’s presidential election, religion has become a deciding factor for many voters, who face a stark choice between a conservative Islamist and a secular former military officer.

The Muslim Brotherhood is presenting its candidate, Mohamed Morsi, as a man of the revolution that ousted Hosni Mubarak and is accusing Ahmed Shafiq, the last prime minister appointed by Mubarak, of trying to return Egypt to the old and repressive order.