It was the first official signal that Egypt may amend the transition plan adopted in the wake of the popularly backed coup that toppled Islamist President Mohammed Morsi.
Backers of the road map have pushed for electing a president first amid continued opposition from Morsi supporters to the current government.
Interim President Adly Mansour had set the timetable in July, calling for a referendum on constitutional amendments first, then parliamentary elections within two months before a vote for the president. The constitution vote is set for January 14-15.