But [ICE chief] Mr. Morton, a career prosecutor, said he was taking a new philosophical approach to detention — that the system’s purpose was to remove immigration violators from the country, not imprison them, and that under the government’s civil authority, detention is aimed at those who pose a serious risk of flight or danger to the community.

Janet Napolitano, the secretary of homeland security, said last week that she expected the number of detainees to stay the same or grow slightly. But Mr. Morton added that the immigration agency would consider alternative ways to assure that those who face deportation — and are not dangerous — do not flee.

Reviewing and redesigning all facilities, programs and standards will be the task of a new Office of Detention Policy and Planning, he said. Dora Schriro, special adviser to Ms. Napolitano, will become the director, assisted by two experts on detention management and medical care. The agency will also form two advisory boards of community groups and immigrant advocates, one focusing on detention policies and practices, the other on detainee health care.

Mr. Morton said he would appoint 23 detention managers to work in the 23 largest detention centers, including several run by private companies, to ensure that problems are promptly fixed. He is reorganizing the agency’s inspection unit into three regional operations, renaming it the Office of Detention Oversight, and making its agents responsible for investigating detainee grievances as well as conducting routine and random checks.

The ACLU is happy about the announced changes, but remains cautious:

“The ending of family detention at Hutto is welcome news and long overdue,” she said in an e-mail message. “However, without independently enforceable standards, a reduction in beds, or basic due process before people are locked up, it is hard to see how the government’s proposed overhaul of the immigration detention system is anything other than a reorganization or renaming of what was in place before.”

Ms. Gupta said the changes at Hutto since 2006 illustrated the importance of enforceable rules. Before the A.C.L.U. lawsuit was settled in 2007, some children under 10 stayed as long as a year, mainly confined to family cells with open toilets, with only one hour of schooling a day. Children told of being threatened by guards with separation from their parents, many of them asylum-seekers from around the world.

Only through judicial enforcement of the settlement, she said, have children been granted such liberties as wearing pajamas at night and taking crayons into family cells. The settlement also required the agency to honor agency standards that had been ignored, like timely reviews of the decision to detain a family at all. Some families have been deported, but others were released or are now awaiting asylum decisions in housing run by nonprofit social service agencies.