BAGHDAD, Iraq _ Groups on both sides of Iraq’s emerging sectarian divide dug in their heels yesterday, with a Sunni Muslim political bloc demanding 25 more seats on the committee that will write the country’s permanent constitution and Iraq’s president and prime minister offering glowing praise for a controversial Shiite Muslim militia.

Iraqi lawmakers have been struggling for weeks to reach an agreement on incorporating more Sunni members. Because Sunnis largely boycotted the country’s legislative elections in January, they are underrepresented in the parliament and have just two seats on the 55-member constitution committee, which is scheduled to hold its next meeting today.

A group of prominent leaders of Iraq’s Sunnis – who, according to most estimates, make up 15 to 20% of the population but often argue that their numbers are higher – met Wednesday and released a statement of prerequisites for their participation in the constitution-writing process.

“We demand 25 seats in the committee so the number would be equal to what the Sunni Arabs represent in Iraq. They form 42% of the community,” Adnan Dulaimi, who heads the government agency that oversees Sunni affairs, said.

That number is almost twice as many added seats as the Shiites and Kurds who dominate the committee have offered. Shiites, who are a majority of Iraq’s population and control its transitional government, have 28 seats on the committee, while Kurds have 15 seats.

“The Kurds expressed their opinion. They do not accept that the number of the Sunnis to be more than theirs,” said Ali Abbagh, a Shiite member of the committee. “Eventually, my advice for them is not to concentrate on the number. They should take part in the presentation of the subjects rather than the number.”

“If they don’t agree at the end, we’ll withdraw from the process of writing the constitution,” Mr. Dulaimi said. “We will never accept the 13 seats they want to give us.”

The Sunnis’ demand could further delay attempts to finalize the membership of the constitution committee, which under the terms of Iraq’s interim charter is charged with completing a draft by August 15. It also underscores the difficult task facing committee members seeking to draft a document palatable to each of Iraq’s main sects. If the committee completes its work on schedule, a national referendum on the constitution would be held on October 15. If not, the committee can request a six-month extension, a prospect both American and Iraqi officials have said they hope to avoid.

“In the referendum, if they don’t agree on our demands, we’ll call on three provinces to reject the constitution,” Mr. Dulaimi said, an outcome that would mean the document “won’t be approved. They will lose their credibility among the people and they’ll be responsible for any delay in the political process. We want to protect the unity of the country.”

Meanwhile, a Shiite militia attempting to recast itself as a political organization, the Badr organization, held its second annual convention in Baghdad. In recent weeks Sunnis have accused Badr of participating in raids and executions carried out against Sunni clerics and political leaders.

Iraq’s Shiite-led government and Badr’s leaders have denied any militia role in the attacks, which have heightened sectarian tensions and threatened to disrupt the fragile efforts to foster political cooperation between the government and Sunni leaders.

“There is a big effort by evil forces to pollute the reputation of the patriotic forces, like Badr organization, to reach goals and desires that stand against the Iraqis’ interests,” said Abdul Aziz al-Hakim, leader of the Supreme Council for the Islamic Revolution in Iraq, a prominent Shiite political party.

The role of nongovernmental militias, which are banned under Iraq’s interim constitution, is expected to be a contentious issue in drafting the permanent charter. Both Badr and the Peshmerga, a Kurdish militia, maintain a visible presence in Baghdad’s streets, many wearing uniforms and toting weapons.

“Badr is a patriotic group that works for Iraq’s interest and it will not be dragged into sectarian or any other kind of struggle,” said President Talabani, a Kurd, who spoke at the conference. “You and [the Kurdish militia] are the heroes of Iraq liberation and you are the strong hands of your Iraqi people.”