The Obama administration intends to announce an ambitious plan on Thursday to overhaul the much-criticized way the nation detains immigration violators, trying to transform it from a patchwork of jail and prison cells to what its new chief called a “truly civil detention system.”

Details are sketchy, and even the first steps will take months or years to complete. They include reviewing the federal government’s contracts with more than 350 local jails and private prisons, with an eye toward consolidating many detainees in places more suitable for noncriminals facing deportation  some possibly in centers built and run by the government.

The plan aims to establish more centralized authority over the system, which holds about 400,000 immigration detainees over the course of a year, and more direct oversight of detention centers that have come under fire for mistreatment of detainees and substandard  sometimes fatal  medical care.

One move starts immediately: the government will stop sending families to the T. Don Hutto Residential Center, a former state prison near Austin, Tex., that drew an American Civil Liberties Union lawsuit and scathing news coverage for putting young children behind razor wire.