BAGHDAD, May 20 -- Iraq's first constitutional government since the fall of Saddam Hussein took office in a televised ceremony Saturday, with unfilled cabinet posts and last-minute sectarian bickering underlining the difficulties it will face in bringing peace and order to the country.
With shows of hands, legislators approved a list of cabinet ministers presented by Prime Minister Nouri al-Maliki. Ministers then took oaths of office, as U.S. Ambassador Zalmay Khalilzad, who shepherded the long-delayed process, looked on.
"The new post puts me and my brothers and sisters in front of exceptional responsibilities," Maliki said in a speech laying out his program. "We will destroy terrorism and tyranny."
The seating of the government completes a process that began in January 2005, when Iraqis elected an assembly to write a new constitution and form an interim government. The Bush administration hopes the new government will take the country's problems into its own hands, confront or win over insurgents and clear the way for a withdrawal of U.S. forces.
Maliki's selection of the cabinet has been a delicate exercise in satisfying the demands of the parliament's Shiite Muslim, Kurdish, Sunni Arab and secular factions. As has often happened in the developing Iraqi government, politicians took months to reach a milestone, then passed it only by putting off difficult decisions until later.
The biggest unresolved question Saturday was who will run the interior and defense ministries, regarded as the country's two most important because they control the police and army. Maliki said that for now he will oversee the Interior Ministry himself, and one of his deputy prime ministers, Salam al-Zobaie, a Sunni leader, will take over the defense portfolio.
Violence continued unabated on the day the government was formed. In the deadliest attack, a pickup truck loaded with explosives detonated in the predominantly Shiite slum of Sadr City in Baghdad, in a square where day laborers gather to look for jobs, police said. Twenty-five people were killed, and 74 were wounded.
The swearing-in took place in a theater where Saddam Hussein once watched a play about an American invasion of the country. The Iraqi national anthem, "My Homeland," played in an endless loop as politicians slowly gathered. Khalilzad shook hands with Iraqi leaders as Western security guards looked on.
While a man read a verse from the Koran, Khalilzad talked to a Sunni leader, then abruptly stood up and left the room. He returned a few minutes later with Adnan al-Dulaimi and Khalaf al-Elayan, two leaders of the main Sunni coalition, who both appeared to be reluctant to attend.
Seconds after the parliament's speaker, Mahmoud al-Mashhadani, began to speak, another Sunni parliament member stood up and asked for two more days to research the cabinet nominees before a vote on them would take place.
Then Saleh al-Mutlak, head of a Sunni group that is not part of the main coalition, interrupted the session again. He declared that Maliki's Shiite coalition had offered him ministries in the government but only if he agreed to change his political agenda. Mashhadani tapped loudly on his microphone to try to stop Mutlak's speech, while grumbling from other parliament members grew louder.
Maliki stood silently at a podium on the stage, waiting to name his cabinet. Once he finally gained the parliament's attention, he listed the 37 names quickly. After that, Mutlak and his party's members walked out of the session, along with several members of the main coalition of three Sunni parties, who protested against swearing in an incomplete cabinet.
The session proceeded smoothly from that point, as parliament members approved each cabinet appointee by raising their hands.
Maliki then outlined a 33-point program. "This government faces three major challenges," he told the gathering, "namely, terrorism and terrorists who are killing people at random without any respect for human life; corruption at all levels by those who are stealing the country's wealth. . . . The third challenge is to provide services for the people."
He also pledged to rebuild Iraq's languishing economy and to guarantee rights to women, prisoners and journalists.
It was unclear whether the walkout of Mutlak's party, which holds 11 seats in the 275-member parliament, and the departure of a handful of members of the main Sunni coalition, would cause serious problems for Maliki's government.
Khalilzad played down the importance of the walkout, observing that 85 percent of the parliament, including most of the Sunni coalition, remained united behind Maliki.
But Abdul Nasser al-Janabi, a member of the Sunni coalition, said that his group would withdraw from the government unless Maliki chose the interior and defense ministers quickly and redistributed other cabinet seats.
After the meeting, Shiite politicians said that the argument was simply part of the trials of a newborn democracy. Several contrasted it to the parliament of Hussein, where political discussions, to the extent they happened at all, were irrelevant.
"You can see today that the Iraqi parliament is not Saddam's parliament," said Mithal Alousi, a secular politician. "There is life there."
In other violence Saturday, a suicide bomber detonated his explosive vest inside a police station in the town of Qaim, 200 miles west of Baghdad near the Syrian border, killing six policemen and wounding 19, said Hamdi al-Aloosi, the director of the Qaim hospital.
The bomber entered the station in civilian clothes, carrying a file folder. U.S. troops cordoned off the area and did not allow anyone to leave or enter the town.
In Musayyib, 40 miles south of Baghdad, police found the bodies of 15 Iraqis in civilian clothes who apparently had been kidnapped and tortured, police Maj. Muhammad Abdul Hassan said.
And in Najaf, a Shiite holy city south of Baghdad, armed men attacked a convoy of Ammar al-Hakim, son of Abdul Aziz al-Hakim, head of the Supreme Council for the Islamic Revolution in Iraq, the largest Shiite political party.
One bodyguard was killed, and two were wounded; Ammar Hakim was not in the convoy, Abdul Hassan said.
Special correspondents Bassam Sebti, Naseer Nouri and K.I. Ibrahim contributed to this report.