CAIRO — Abdel Fattah el-Sisi, the former general who led the military takeover here nearly one year ago, was sworn in as president on Sunday, testing the bet that a new strongman can overcome the economic dysfunction and political polarization that bedeviled Egypt’s three-year experiment with democracy.

In an address to dozens of visiting heads of state gathered in a gilded presidential palace, Mr. Sisi pledged to work for security and stability in Egypt and the region.

“It is time for our great people to reap the harvest of their two revolutions,” he said, referring to the 2011 uprising that forced out President Hosni Mubarak and the 2013 protests that preceded the military takeover.

Mr. Sisi, 59, now takes formal responsibility for a nation racked by three years of turmoil, scarred by the new government’s bloody crackdown on the Muslim Brotherhood and riven by deepening loathing between rival Islamist and nationalist factions of the population. Without billions of dollars in continuing aid from Persian Gulf monarchies glad to be rid of the Brotherhood, Egypt’s Treasury would empty and its economy collapse.