Federal prosecutors have asked a U.S. District Court judge here to compel the District of Columbia to provide decent living conditions, training and homes in the community for the 400 patients at Forest Haven, the problem-plagued D.C. facility for the mentally retarded.

Conditions at the facility in Laurel are "indefensible and egregious" and as a result patients "are suffering genuine harm," the prosecutors said in a motion filed with Judge John H. Pratt.

A team of federal prosecutors, headed by U.S. Attorney Charles F. C. Ruff and Acting Assistant Attorney General James P. Turner, said in the motion that Pratt ordered the city government to make massive improvements at Forest Haven more than two years ago, but that the city had not made the changes because of what the prosecutors concluded was "administrative chaos" within the D.C. government.

The federal government, intervening on behalf of patients in a class action suit brought by the Urban Law Institute of Antioch Law School, said that conditions for the patients are not likely to improve and urged the judge to conduct an immediate hearing on the city's compliance with his order. "Further delay is intolerable in view of the gravity of current problems at Forest Haven," the motion said.

"Overall, the facility is in gross non-compliance with the major provisions" of Pratt's 1978 order, the prosecutors charged. They said the 56-year-old institution suffers from inadequate staff, equipment and management.

Pratt's order had required the city to conduct an annual assessment and implement a rehabilitation plan for each patient. But the prosecutors contended that a majority of residents "have as yet received neither one" and "even where programs have been prescribed, they are generally not being implemented."

City officials either declined comment or were unavailable.

Prosecutors said they had taken depositions from a half dozen officials of the D.C. Department of Human Services (DHS) and visited Forest Haven repeatedly, finding that:

Missing supplies were a major problem. There was a lack of detergent, toilet paper, sheets, blankets and diapers. One dormitory bathroom had no toilet paper or toilet seats, and no supervision. "An order for wheelchairs, placed in February 1980, was 'found' in the DHS budget office in November and was still unfilled in December; other orders have taken from six months to one year to be filled."

No food was purchased for a two-month period last year, forcing the Forest Haven superintendent, in his own words, to "scurry around and borrow and beg" for food, prosecutors said. Because of administrative delays in requisitioning, the institutional pharmacy frequently ran out of necessary medicine, including drugs designed to remedy convulsions.

Because of inadequate planning and staff, Forest Haven residents "spend their days in idleness . . . the typical scene on the wards . . . is unchanged; virtually no activity occurred four years ago, and virtually none occurs now."

One of every six staff positions is unfilled; last year the facility lost 64 employes. Recruitment has stopped because of Mayor Marion Barry's hiring freeze and the mayor has refused to grant an exception for Forest Haven. The prosecutors said the city has not sougth outside contracting services to help give patients minimal staff care.

"Since adequate supervision cannot be provided, accidents and injuries are commonplace," the prosecutors wrote in their motion filed last week. "The records for 1980 document numerous bruises, cuts, bites and fractures, and even an instance in which a resident was beaten unconscious."

The city's budget requests are insufficient to permit improvement of conditions. "What is disturbing is that the defendants have not taken . . . basic commonsense steps," the prosecutors wrote.

Forest Haven has long been the target of complaints by citizens and federal and local government officials. Federal officials last month rescinded accreditation of the institution, cutting off about $6 million in annual Medicaid payments, because it does not meet U.S. standards for patient care.