BAGHDAD, Iraq -- Khalid al-Mashadani pounded on the white gate of his house.

Two years ago, he was among thousands of Sunnis driven out of Baghdad's Hurriyah neighborhood by Shiite militiamen in one of Iraq's worst eruptions of ethnic bloodletting. Shiite families soon occupied Sunni houses. In late September, Mr. Mashadani came back for the first time, along with Iraqi soldiers, determined to recover his property.

A Shiite man and his wife stepped out, their faces infused with fear, and said they were renting the house. Angrily, Mr. Mashadani informed them that he was the owner. "This is illegal," he shouted.

An Iraqi army officer ordered the family to report to a nearby military outpost, a step that could lead to their eviction.

"What do you want from us?" the wife pleaded.

Across Baghdad, Iraqis are trickling back to onetime sectarian killing zones to reclaim their houses and former lives. While Sunnis are emboldened by a sharp decrease in violence and protection from the Iraqi government, many wonder whether they can trust the predominantly Shiite security forces and whether they can resume living among neighbors who once sought to kill them.

"It will take a very strong law to bring Sunnis back to Hurriyah," said a senior Shiite police official who would give only the nickname Abu Ahmed. "As Iraqis, it is difficult for us to forget those who were killed. It needs a long time."

Since the 2003 U.S.-led invasion, more than 5 million Iraqis -- one of five citizens -- have fled their homes, according to the International Organization for Migration. Only a small fraction have returned.

In Hurriyah, of the more than 7,000 Sunni families who fled in late 2006, roughly 325 have reclaimed their houses, mostly in the past month. A middle-class enclave in western Baghdad, Hurriyah is a sprawling jigsaw of tan mosques, shop fronts and modest houses.

U.N. officials and human rights groups are concerned that a speedy resettlement could touch off new strife, in part because sectarian segregation has helped to reduce violence. Already, Shiites who occupied Sunni houses are being pushed out, often by force, and returning Sunnis have come under attack. U.S. military officials, wary that a sudden influx of returnees could undermine security gains, say they are proceeding carefully.

"This will be a long and controlled process," said Col. William B. Hickman, commander of the 2nd Brigade Combat Team, 101st Airborne Division, which is working with Iraqi security forces to bring Sunnis back to Hurriyah.

As Mr. Mashadani, a former member of Iraq's parliament, walked away from his still-occupied house, his Shiite neighbors greeted him with smiles and handshakes. "We're waiting for you to come home," one woman said.

"Inside I know they feel different about me," Mr. Mashadani said later. "They are the same people who drove me out."

The week before last, two dozen tribal leaders from Hurriyah met at an Iraqi army base in Baghdad's Khadhamiya neighborhood. They sat at a long table, with Sunni leaders largely one side and Shiites on the other. Col. Hickman and Brig. Gen. Sameer al-Iqabi, the top Iraqi commander in eastern Baghdad, tried to convince the leaders to return to Hurriyah from an area called Tarmiyah, about 30 miles north of Baghdad.

But the Sunni leaders were concerned that Iraqi security forces would arrest returnees they suspected of being insurgents. Gen. Iqabi promised that any arrests would follow proper legal procedures.

Some of the Sunnis wanted the Shiite tribal leaders to provide guarantees of protection. But the Shiites said they could not offer that.

Since the expulsion in 2006, Sunni extremists have attacked Shiite homes, staged kidnappings of Shiites and set off bombs in Hurriyah.

"My force and I will protect those coming back," Gen. Iqabi said.

A Shiite tribal leader wearing a white-checkered headdress and dark glasses raised his voice.

"If those who committed bloodshed come back, there will be a big problem. There will be more bloodshed. There are a lot of victims in Hurriyah," warned Jalil Khuribut al-Bidhani. "We should not let the families of the killers back."

"When they are back, justice will be done," Gen. Iqabi promised.

Salman Mahmud Hamadi, a Sunni, shot back: "And how about the other side? If the killer still lives there? If I return and see the man I know who killed my son? What happens then?"

One day last month, Ahmed Gizhar, 54, and his wife Salwa Mizher, 45, walked into Farook Mosque, a Sunni shrine that is now an Iraqi army base. For two years, the couple occupied a Sunni house in Hurriyah. That morning, six Sunni men representing the owner gave them three days to leave. Mr. Gizhar came to the base to complain to the government that was backing his eviction.

"What can I do?" Mr. Gizhar asked 2nd Lt. Hussein Rahim, 38, a burly man with a thick moustache. "I am sick. We cannot afford to rent a house."

Mr. Gizhar, who needs a cane to walk, said he owned three houses in Khan Dari, a town north of Baghdad, but he couldn't return because Sunni insurgents controlled the area. "If I go back, they will behead me," Mr. Gizhar said, crumpling into tears.

He bent over. His hands cupped his face, his body shook. "I hope to die. I hate my life. Death is better than living like this."

Mr. Gizhar demanded to know Lt. Rahim's sect, but the soldier would say only that he was "Iraqi."

"The law should be fair to all the people," Mr. Gizhar said. "You pushed me out of this house but you didn't push out those who are in my houses."

Lt. Rahim finally told Mr. Gizhar to seek help from friends or relatives or share the rent of a new place with another family.

"But don't occupy another empty house," Lt. Rahim warned.

The Sunni couple entered their house in Hurriyah last month with bags in their hands and fear in their hearts. Their furniture was gone. Electric sockets were torn out. An old rifle dangled from a ceiling hook. The couple saw it as a warning left behind by the Shiite family who had occupied their home until soldiers forced them out.

But Abid Mehdi, 65, and his wife Hamdia Ali, 55, had come to stay. In Tarmiyah, they lived in a tiny mud and clay house surviving on handouts and Mr. Mehdi's small pension. Kinsmen ridiculed them for not standing up to Shiites.

"We are afraid, but we have no other solution," Ms. Ali said, seated on the cold cement floor of their bare living room.

A couple of neighbors welcomed them with food. One sent over a rickety fan, another an ancient television. But many of their Shiite neighbors have remained distant.

"Most don't like us," Ms. Ali said, tears welling in her eyes. "We are Sunnis. Nobody likes Sunnis."