WASHINGTON -- The Obama administration plans to place federal employees in the largest immigration detention facilities in the country to monitor detainee treatment.

This oversight role is currently handled by private contractors. But under the new plan, Immigration and Customs Enforcement officials would be placed at the largest jails to directly supervise how the detention centers are managed, according to people briefed on the government's plan.

The government has been criticized for its treatment of immigration detainees, and Homeland Security Secretary Janet Napolitano has made detention policies a top priority for her department.

ICE, which is part of Homeland Security, intends to hire a medical expert to review the health care protocols for the detention centers and give an independent review of medical complaints, according to the people briefed on the plan. They spoke only on condition of anonymity ahead of an announcement expected Thursday.

Shortly after Napolitano became secretary, she created a new advisory position to focus on detention issues and arrest priorities at ICE. Napolitano, formerly the Arizona governor, named a former head of Arizona's Corrections Department, Dora Schriro, to the post. As part of its plan, the department will create yet another new position to be filled by Schriro: director of the Office of Detention Policy and Planning.

Some immigrant advocates have said the federal government has failed to meet its own standards for detaining immigrants, making it unduly difficult for immigrants to defend themselves in court and fight to remain in the country.

A report released last month by the Los Angeles-based National Immigration Law Center found that detainees have faced limited access to phones, mail and law libraries in violation of federal standards. The authors based their findings on more than 18,000 pages of documents that showed facilities across the country limited detainees' access to legal materials and transferred them without proper notice.

The agency also has been criticized for failing to provide proper medical care to detainees resulting in the deaths of some detainees and congressional hearings.

The department was forced to make changes in 2007 at the T. Don Hutto Facility, a family detention center and former prison in central Texas where young children are held with parents.

Attorneys sued on behalf of children alleging guards working for the private prison company that runs the center disciplined children by threatening to separate them from their parents; the school day was just a few hours and families had little privacy living in cells with two bunks and a steel toilet, among other things.

Detention has grown in recent years, with the federal government holding more than 32,000 detainees each day. Over the last four years, the budget for keeping immigrants in custody has nearly doubled to $1.7 billion, according to ICE.