CAIRO — Egypt’s most powerful political force, the Muslim Brotherhood, may be splintering.

The influence and organizational abilities of the Islamist group have raised fears in the West and among some secular and liberal groups in Egypt that the path to democracy in the country may instead end with an Islamic state. But the historically unified movement, long considered the only viable opposition to Hosni Mubarak, has struggled to adapt to the new political landscape that has emerged since his ouster in February.