Top administrators at Great Oaks Center, Maryland's second largest institution for the mentally retarded, were relieved of their duties there yesterday after a state review found what it called a "significant . . . management problem" weeks after an employe union asked for an investigation of the facility.

The center's director, Clifford Lockyer, and deputy director, Paul Joyce, were informed yesterday of the findings of the internal investigation and told that because of those findings they would be reassigned within the state's Mental Retardation/Developmental Disabilities Administration.

Lockyer, who has been both directing activities at Great Oaks in Silver Spring and coordinating community programs for several counties in southern Maryland, now will handle only the community programs, state officials said. No position has yet been determined for Joyce, spokemen said.

Neither Lockyer nor Joyce was available for comment, according to a spokesman for the state Department of Health and Mental Hygiene.

The team's report, which was released yesterday, found "no basis for believing that substantial management improprieties took place at Great Oaks.

"However, the committee did find that there exists at Great Oaks a significant long-term employee management problem," the report said. "This problem, which seems to be pervasive within the institution and includes both professional and non-professional employees, appears to be the basis for rumors of impropriety."

Edward F. Orndorff, the head of special assignments for the western section of the state, was named as acting superintendent and will take over duties at Great Oaks on Monday, a spokesman said. Orndorff has previously been the administrator at two other state facilities.

The administration overhaul comes almost a month after representatives of the American Federation of State, County and Municipal Employees charged that Great Oaks administrators had failed to properly investigate allegations of abuse, mismanaged purchasing records and used state property for personal purposes.

In one episode addressed in the report, Joyce and another unnamed administrator directed subordinates to exercise a mentally retarded adult through the night so he could be transported to California with minimal problems.

Union representatives claimed the client had been abused by being forced to stay awake and by being exercised. The state yesterday found that the incident reflected "poor judgment" but "falls short of alleged client abuse."

The state investigation team, appointed by state Secretary of Health and Mental Hygiene Adele Wilzack, interviewed about 20 employes and administrators at the center during the last two weeks.

Thomas Ridgley, union representative for AFSCME Council 92, said yesterday that he was pleased with the state's action and was sure that employe morale will benefit.

"I don't think charges of this magnitude can be glossed over," Ridgley said. "We're concerned with the well-being of the clients, and all we asked for were the kinds of conditions to give the proper care."

Great Oaks, a facility for about 450 mentally retarded children and adults, accepted its first clients in November 1970.

Lockyer, 58, had been its director since May 1973. Joyce, who has been employed by the state since 1973, was named deputy director in October 1976.

According to an internal letter to Wilzack from Trevor Hadley, assistant state secretary for mental health and an adminstrator who reviewed the investigation report, as many as three more administrators may be assigned to the facility.

In the letter dated Oct. 10, Hadley said, "The situation at Great Oaks has deteriorated . . . in part because of the lack of sufficient management staff."

Hadley recommended that the director of Great Oaks no longer be responsible for state community programs, a point that was adopted yesterday in Lockyer's new appointment.

Hadley also said the deputy director should not be responsible for residential care but should be given the more "traditional function" of managing business, dietary and maintenance operations.

A new position of director of residential care should be established, he said. In addition, another position of director of clinical services should be established.

Both those positions would be equal in rank to the deputy director, Hadley recommended.

A spokesman for the Department of Health and Mental Hygiene said yesterday that no decision had been made about the establishment of the new positions.