Mr. Aboul Fotouh’s liberal understanding of Islamic law on matters of individual freedom and economic equality had already made him the preferred candidate of many Egyptian liberals.

His endorsement on Saturday by the Salafis now makes him the candidate of Egypt’s most determined conservatives, too. Known for their strict focus on Islamic law, the Salafis often talk of reviving medieval Islamic corporal punishments, restricting women’s dress and the sale of alcohol, and cracking down on heretical culture…

Salafi leaders described their decision in part as a reaction against the presidential candidate of the Muslim Brotherhood, the powerful and established Islamist group that now dominates Parliament. Though more moderate than the Salafis, the Brotherhood also favors the fashioning of an explicitly Islamic democracy in Egypt, and on social and cultural issues the group is closer to the Salafis than Mr. Aboul Fotouh is.

But in television interviews on Saturday night, some Salafis said they believed the Brotherhood’s current candidate, Mohamed Morsi, was weaker than either Mr. Aboul Fotouh or the Brotherhood’s original nominee, Khairat el-Shater. Others said the group was wary of giving a monopoly on political power to the Brotherhood, which recently abandoned its pledge not to seek control of the presidency as well as the Parliament.