A moderate Islamist group that was brutally repressed for decades was poised Monday to become Tunisia’s dominant political faction after a landmark election to choose a council that will draft the country’s new constitution and appoint an interim government.

At Ennahdha’s headquarters in the capital, women ululated and young men sang to celebrate the group’s strong showing. But party officials said the challenges ahead are considerable. After preliminary results showed the group — its name means “renaissance” — receiving far more votes than any other party, Ennah­dha politicians said they would have to move quickly to convince voters that their trust was well placed.

Official election results were not expected until Tuesday afternoon, but preliminary information from polling places leaked to a local radio station showed Ennahdha leading among most constituencies. The party took half of the 18 seats reserved for overseas Tunisians, official preliminary results showed.

International and domestic observers said the elections were free and fair.

The likely outcome of the first free vote spawned by the Arab Spring suggested that Islamist parties and their charitable networks, long suppressed by autocratic leaders, hold great appeal in a region beset by unemployment. Promises by Islamists of greater social justice have stood in sharp contrast to the corruption of the leaders toppled by revolts this year.

Ten months after Tunisians rose against the regime of Zine el-Abidine Ben Ali, sending shock waves through the Arab world, voters are hopeful that the election results will eventually translate into new jobs and greater prosperity.

But Ennahdha officials also understand the tremendous symbolism of the vote. Party officials and other Tunisians said they hope it will send a message to the West and their Arab neighbors that a democratic system can coexist with Islamic values.

“What’s unique here is we have a formal Islamist group or movement who are trying to offer a new model which puts democracy and Islam together,” said Said Ferjani, a member of Ennahdha’s political bureau. Ferjani was imprisoned and tortured during Ben Ali’s regime before living in exile for 22 years. “Islamist is when you serve the people who rightly elected you.”

The party ran a strong campaign across the country. It reached not only the religious, but also socially conservative voters who saw it as an authentic Tunisian party that respects the Arab and Islamic character of the nation, analysts said. Some here resent the secular elite, who expect people to speak and conduct business in French.

“Clearly Ennahdha picked up the vote from people who may not, in their heart of hearts, consider themselves moderate Islamists,” said Christopher Alexander, a Tunisia expert at Davidson College. He called the party a “battering ram” for Ben Ali’s regime, which arrested and tortured its members and used the group to stoke fear of an Islamist takeover.

Tunisia, known for decades for its harsh repression of dissidents, also has long had the most progressive laws on women and families in the Arab world. Some secularists fear that if Ennahdha were to win a majority of the seats in the assembly, such laws would be reversed. But the party has promised to respect the laws on marriage and divorce and work toward women’s rights, human rights and a solid democratic system.

“The best way to deal with the Islamists is to include them in the process,” said Marwan Muasher, vice president for studies at the Carnegie Endowment for International Peace and an election observer with the National Democratic Institute. “There’s no excuse for keeping them out.”

In stark contrast to the Islamists’ success was the apparent poor performance of the secular Progressive Democratic Party, the strongest legal opposition under Ben Ali’s government. The PDP ran a campaign that cast its leaders as the protectors of secular and modern values. Dozens of parties were on the ballot, and secularists were divided among many of them. On Monday, the PDP conceded its loss and pledged to work in the opposition rather than with Ennahdha.

“We congratulate the winning party and wish them good luck in fulfilling their promises to meet the demands of the poor and the unemployed within nine months to a year,” PDP leader Nejib Chebii said at a news conference, referring to the constitution-writing assembly’s time frame.

Ennahdha expects 42 percent to slightly more than half of the council seats. Some within the party worry that an outright majority would push the burden of Tunisia’s daunting problems squarely on their shoulders.

“Are we going to do well in terms of putting up this democracy? Are we going to do well with the West and U.S.?” Ferjani said, referring to how people will measure the party’s performance. “People will expect from us and anybody in office to lay a very strong foundation and deliver a political democratic system in a place that cares about majority and minority alike.”

Ennahdha and other factions are in discussions about how to run a multiparty consensus government while the assembly writes the constitution. Ferjani said the party would want the position of prime minister, who appoints the cabinet, as well as service ministries such as education, health and development to fulfill campaign promises of enhancing social services.

“We are in internal discussions and reaching out to other parties for a coalition government,” said Intissar Ghannouchi, the daughter of the party’s head, Rachid Ghannouchi. “People voted for credibility and went to parties with a long track record of those committed to the struggle against dictatorship.”