CAIRO — As his supporters in Tahrir Square were chanting on Sunday for the end of military rule in Egypt, the country’s president-elect, Mohamed Morsi, had glowing words for none other than the army, saying he regarded it with a “love in my heart that only God knows.”

Mr. Morsi’s remarks, during his first address to the nation after his victory was announced, were an acknowledgment of his new, changed role. He had gone from being a representative of a banned Islamist group to the leader of a nation and its public’s chief negotiator with the military generals who assumed power after the ouster of President Hosni Mubarak in February 2011.
As the first freely elected president of Egypt, Mr. Morsi has a historic opportunity, but he faces a litany of challenges that could prevent him from becoming more than just a figurehead. He will have to spar with the generals, who, just after the election, stripped much of the power from the presidency, and he must overcome the doubts of those who chose his opponent — nearly half of the voters — and millions more who did not vote.
Mr. Morsi will also have to convince Egyptians that he represents more than just the narrow interests of the Muslim Brotherhood and to soothe fears among many that his true goal is to bind the notion of citizenship itself more closely to Islam.
“The challenges are very strong,” said Mohammed Habib, a former deputy chairman of the Brotherhood who has worked with Mr. Morsi. “Everyone is watching him through a microscopic lens.”
Asked if Mr. Morsi had what it takes to overcome those challenges, Mr. Habib said, “No, he doesn’t.”
Mr. Morsi, 60 an engineer with a doctorate in materials science from the University of Southern California, taught engineering at another California college and at Zagazig University in the Nile Delta.
A lackluster, accidental candidate, he was chosen to run after the Brotherhood’s first choice, Khairat el-Shater, was disqualified.
Married with five grown children, Mr. Morsi has a reputation as a religious conservative and a company man, an enforcer for the group who brooks little internal dissent. During the campaign, he portrayed himself as a defender of strict religious values one minute, a moderate courting liberals the next — doing little to burnish his reputation.
“Morsi is an accident of history. He’s a fairly unremarkable guy,” said Shadi Hamid, a fellow at the Brookings Doha Center. “I guess the real question is, can he change?”
Mr. Morsi’s first test will come immediately. Brotherhood leaders have said that thousands of their supporters will continue to occupy Tahrir Square until the Parliament, which the military council dissolved last week, is reinstated. The military rulers have said that elections will be held for a new Parliament, although those ousted were seated in January. On Sunday, Mr. Morsi threw down his first challenge to the military, saying he would be sworn in only in front of the Parliament whose members were just dismissed. He once served as the head of the Brotherhood’s parliamentary bloc.
Leaving aside Egypt’s all-consuming problems, especially its sputtering economy, Mr. Morsi will face specific governing challenges, especially enlisting partners from other parties who have been reluctant to work with the Brotherhood and dealing with the groaning state bureaucracy bequeathed to him by Mr. Mubarak.
“This is not like running a party or a group,” Mr. Habib said. “This is very big.”
Mr. Habib said Mr. Morsi would have to deploy “reconciliatory rhetoric,” to coax former presidential candidates like Hamdeen Sabbahi, a leftist, or Abdel-Moneim Aboul Fotouh, a former Brotherhood leader, to work with him. “He must strengthen his relationship, and restore the confidence of the national parties,” Mr. Habib said. “Otherwise they will cause him trouble and pull the carpet from underneath his feet.”
Mr. Morsi faces scrutiny over his relationship with the Brotherhood. He resigned from the group on Sunday, but many people believe his years in the organization mean his ties to it will persist. During his campaign, Mr. Morsi never made a major decision without the approval of the Brotherhood’s guidance council. Mr. Shater, the group’s leading strategist whose disqualification led to Mr. Morsi’s running, is seen as especially influential.
“He has a chance to become his own man, but he has to distance himself from the Brotherhood,” Mr. Hamid said. “At some point, Mr. Morsi is going to start making his own decisions, and sooner or later, there will be tensions between Shater and Morsi.”
Mr. Habib put it more bluntly. “He must be completely independent,” he said. “There is no choice.”
In his speech on Sunday, Mr. Morsi did not mention the Brotherhood, though he did reach out to Christians, who formed a pillar of support for his rival, Ahmed Shafik. Mr. Morsi, who has said women and non-Muslims should not serve as president, again tried to broaden his appeal.
“We as Egyptians, Muslims and Christians,” he said, “we will face together the strife and conspiracies that target our national unity.”
David D. Kirkpatrick and Mayy El Sheikh contributed reporting.