The constitutional process, along with attempts to open channels with some militant groups not tied to extremists, is touted by the United States and Iraq's government as a way to help defuse the insurgency.

''Those who are terrorists, those who are al-Qaida and [Jordanian-born terrorist leader Abu-Musab] al-Zarqawi, and those who are Saddam elements, we have [nothing to] say to them,'' Iraqi President Jalal Talabani said Thursday. ''But other Iraqis who are dissatisfied with something . . . we are ready to listen to them and permit them to come back to the democratic process in Iraq.''

A key lieutenant of al-Qaida in Iraq, the terrorist group led by al-Zarqawi, had been apprehended by the multinational forces in the northern city of Mosul, the miltary announced Thursday. Air Force Brig. Gen. Donald Alston, the chief spokesman for the U.S.-led military force in Iraq, said that Mohammed Khalaf, known as Abu Talha, was captured Tuesday without a fight, though he had vowed not to be taken alive and was known to wear an explosive vest at all times.

The breakthrough in bringing minority Sunni Arabs into the constitution-writing process bridged a division between leaders of the 55-member constitution committee, who had offered to add 13 Sunnis to the two already on the panel, and Sunni groups that demanded 25 be added. Under the compromise announced Thursday by committee leaders, the new panel will include the members of the existing committee, 15 additional Sunni Arabs with full voting rights and 10 more Sunnis in an advisory, nonvoting role.

''The problem is solved and ended. The Sunnis will participate in the process of writing the constitution,'' said Tariq Hashimi, the secretary general of the Iraqi Islamic Party, a leading Sunni Arab organization.

Iraq's Sunni Arabs, who held the bulk of power in Iraq under empires, monarchies and dictatorships spanning centuries, boycotted January's parliamentary elections and hold relatively few seats in the 275-member National Assembly. When the Shiite Muslim coalition that holds a majority in the assembly formed a constitution committee in April, only two Sunni Arabs were included.

Since then, leaders from across Iraq's political and sectarian spectrum have been working to ensure that more Sunni Arabs have a role in writing the constitution, which must be completed by Aug. 15.

The U.S. military reported, meanwhile, that a roadside bombing killed five Marines on Wednesday near Ramadi. An American sailor serving with the Marines in Ramadi was also killed by gunfire Wednesday.

The deaths of American service personnel near Ramadi added to a sharp increase in U.S. casualties in Anbar province, a vast area that stretches from Baghdad's western edge to the country's borders with Syria, Jordan and Saudi Arabia. Ramadi, the provincial capital, has been a center of Iraq's insurgency for more than a year.

Military spokesman Alston said the arrest of al-Zarqawi's top aide was made possible by tips from local residents. Since al-Zarqawi declared in May that it was permissible to kill civilians in attacks against security forces, Alston said, ''we are getting reporting that cells, as part of his network, are concerned about the consequence of this behavior and the consequence of what they've done to the Iraqi people. The Iraqi people increasingly are exposing the insurgents.''