The Muslim Brotherhood, the Islamist group that supports Mr. Morsi, said that around 57 percent of those who cast ballots in the first round on Saturday voted in favor of the proposed constitution, whose drafting was dominated by Islamists. The figure was based on unofficial tallies. A second round of voting is scheduled for this Saturday in rural areas, where the draft constitution is likely to win stronger support.
While the Brotherhood hailed the “political maturity” of voters, opposition leaders disputed the unofficial results and said the voting was marred by irregularities. Each side sought to frame the results as favorable.
Although many people here predicted that the charter would be approved, the turnout was just 31 percent, according the Brotherhood’s estimates. That immediately raised doubts about whether a document intended to express a consensus on Egypt’s identity and lay the foundation of a new government had won legitimacy in the referendum.
Some also said that the low turnout and relatively narrow approval margin dented assumptions about the strength of the Brotherhood, whose extensive grass-roots network had yielded a string of electoral victories since President Hosni Mubarak was toppled in February 2011.
Some Brotherhood officials seemed surprised by the results. “It’s certainly below a lot of expectations,” said Gehad el-Haddad, a senior Brotherhood official. He and others said the polarizing political fight between Mr. Morsi’s supporters and opponents was to blame, causing a broad disillusion with politics and prompting what Mr. Haddad called Egypt’s “silent majority” to stay home.
Still, he argued that the high proportion of “no” votes came not from a rejection of the draft constitution, but rather from anger — justified or otherwise — at the Brotherhood.
“The evaluation was not on the product,” he said. “It was on the producers.”
Resentment against the Brotherhood grew in recent weeks after Mr. Morsi issued a decree insulating his decisions from judicial scrutiny and then hastily called a referendum on the constitution. Many Egyptians also blamed the Brotherhood for deadly clashes outside the presidential palace two weeks ago.
The voting on Saturday was largely peaceful, a respite after weeks of turmoil and a toxic political debate over the constitution.
The arguments started again on Sunday. A coalition of human rights groups called for a revote, saying there were thousands of complaints of violations at the polls and inadequate supervision by judges. The Brotherhood-sponsored Freedom and Justice Party also cited allegations of misbehavior by opponents at polling places, but said that in general the voting was a success. The Egyptian election commission said it would release official results after the second round.
Some opposition figures were hailing the results of the referendum as a small victory for non-Islamist political groups. Amr Hamzawy, the founder of the liberal Free Egypt Party, asserted in a message on Twitter that the relative closeness of the outcome ended the notion that the Brotherhood was unbeatable at the polls. “Saying that democratic currents have no popularity, and that the Brotherhood and their allies monopolize popular will and have the license of the boxes fell yesterday, once and for all,” Mr. Hamzawy wrote.
But analysts said that the voting had left an uncertain landscape. A much better showing for the draft constitution in the next round would probably strengthen Mr. Morsi’s hand. But if current voting patterns continue, Mr. Morsi would just as surely face steep challenges in governing. The Brotherhood could also be seen as more vulnerable in parliamentary elections due after the constitution is adopted.
Mr. Morsi’s problems could start with the charter itself. If it passes narrowly with only about one-third of eligible voters turning out, the document would have legal legitimacy, “but it’s difficult to argue it would have popular legitimacy,” said Zaid al-Ali, who has tracked Egypt’s constitution-writing process for the International Institute for Democratic and Electoral Assistance, based in Sweden. “Politically, it will be a hot potato for a long time to come,” he said.
Many countries require that constitutional referendums exceed a minimum turnout threshold to be valid, out of a belief that the fundamental nature of constitutions means that they must command broad popular support.
Some members of Egypt’s constitutional assembly seemed to agree in principle. Mr. Ali said that several members had told him that they would not be satisfied unless half of eligible voters — not just half of those casting ballots — registered approval. One member was quoted in state news media saying a two-thirds majority in favor was needed for legitimacy. But no such requirements were imposed.
A narrow outcome would oblige the president to “spend a large proportion of his time defending its legitimacy, rather than discussing specific policies,” Mr. Ali said.
Some saw the voting as a referendum not just on the charter, but also on the president’s record after five months in office. “I read this as a strong vote against the dismal, confused performance of the Morsi administration,” said Emad Shahin, a political scientist at the American University in Cairo, about the low turnout and high proportion of “no” votes. Of the president’s Islamist allies, Mr. Shahin said, “I think they thought they were on their way to really secure some kind of comfortable majority for the constitution, which did not happen.”
Whether that assessment is borne out remains to be seen. But Mr. Shahin said that the results so far already showed the need for Mr. Morsi to change his approach to his opponents, who have faulted him for failing to build consensus around contentious decisions. He said that Mr. Morsi’s government needed a transformation of “mentality”: from a state run by the Muslim Brotherhood to a “state that runs an entire country with its all political and social segments.”
Mr. Shahin laid equal blame on the opposition, for resorting to obstructionism rather than compromise at crucial junctures. He called some of the opposition leaders “irresponsible” and said they had engaged in a “massive campaign of disinformation” about the constitution, aided by segments of the news media.
Late on Sunday, opposition leaders signaled that they intended to keep the pressure on Mr. Morsi, calling simultaneously for a large protest on Tuesday, for voters to turn out heavily in the second round next Saturday and for the election commission to consider voiding the first round because of the irregularities.
David D. Kirkpatrick contributed reporting.