District Mayor Anthony A. Williams said yesterday that he will appoint a coalition of private groups to temporarily manage the care of the city's mentally retarded wards. The move, which effectively strips day-to-day supervision of the wards from a D.C. agency, is part of what Williams said will be an overhaul of the group home system.

The Lt. Joseph P. Kennedy Institute, a nonprofit with a 50-year history of working with the mentally retarded, will lead the coalition that will take over case management duties while a new management team is established for the city's mental retardation agency. City and institute officials still were negotiating the terms of the takeover yesterday, but Williams's office indicated that the Mental Retardation and Developmental Disabilities Agency's existing budget would cover the changes.

Williams's move reflects his lack of confidence in the mental retardation agency, which his office has been investigating since last month, when The Washington Post reported that since 1993, not one of the 116 deaths in homes for the mentally retarded had been investigated. In addition, a former worker in the Department of Human Services--which oversees the mental retardation agency--admitted to shredding documents concerning a problem death after The Post asked questions.

On Tuesday, Williams fired five top managers in the mental retardation agency and suspended two others. Yesterday, Williams fired Jesse P. Goode, the general counsel for Human Services. Goode's firing surprised some advocates for the retarded, who considered him a supporter of reform at the embattled department.

The mayor said yesterday that there may be more firings in the Human Services and Health departments.

"To those who have shirked your responsibility, you're going to be held accountable," Williams said at a news conference. "This is the first step in an aggressive effort to improve services and protect our most vulnerable citizens."

Protecting the District's most fragile residents was a theme that Williams reiterated yesterday. Besides announcing his plans to reorganize services to the mentally retarded, the mayor took aim at the city's much maligned foster-care system for its role in the death this month of 23-month-old Brianna Blackmond.

Brianna, who was in foster care because her biological mother had been deemed neglectful, was killed by a blow to the head less than two weeks after a D.C. judge ordered the girl returned to the mother. It is unclear why D.C. Superior Court Judge Evelyn E.C. Queen sent Brianna home in December without a court hearing; Queen had indefinitely postponed the hearing and never saw a report from the District's Child and Family Services Agency recommending that the toddler not be sent back to her mother.

"That poor child died because adults couldn't get their act together," said Williams, a former foster child who grew up with his adoptive parents. "I am deeply, deeply saddened. I'm aghast this could happen. It is shocking and inexcusable."

The mayor stopped short of saying what exactly he planned to do in response to Brianna's death. Because the foster-care system operates under a court-appointed receiver, the mayor's role in running it is limited.

D.C. police officials said yesterday that they are continuing their investigation into Brianna's death.

Williams released a 39-page report yesterday on his administration's probe of the group home system. The report found that the many agencies that make up the city's mental retardation service system have created a "highly dysfunctional" operation that "is incapable of providing quality service."

The report paints a picture of the Human Services mental retardation agency as having little accountability to the clients it serves. Workers with no training or experience are given jobs crucial to the safety of the retarded. And when those workers fail to perform, Human Services managers--themselves lacking training and skills--routinely give them "excellent" job evaluations. Meanwhile, allegations of abuse or neglect have gathered dust on the desks of overworked department investigators.

The mayor has hired a new director for the mental retardation agency, Beverly Doherty, who is moving from Wisconsin to take over the agency on Jan. 30. G. Keith Chadwell, an administrator with the Virginia Department of Social Services, will become the new chief operations officer for Human Services.

D.C. Council member Kathy Patterson (D-Ward 3), chairman of the government operations committee, praised Williams's administration for taking a hard look at the city government's own failings.

"This report was not from the [federal] GAO or the inspector general, but from the government itself," Patterson said.

For years, Williams said, the government has looked the other way when disabled people were abused and neglected. "This has to stop," he said.

"We're not going to live in denial," Williams said. "We're not going to run and hide from the truth."

CAPTION: Mayor Williams listens as Deputy Mayor Carolyn N. Graham tells what is being done to improve services for the retarded.