The Maryland secretary of health has fired two top aides in the department that oversees facilities for the mentally retarded, including the chronically troubled Great Oaks residential facility in Silver Spring.

Last week, Secretary of Health Carles R. Buck fired Theodore G. Lucas, assistant secretary for special programs, and John F. Monaghan, director of the department's mental retardation administration.

Henry G. Nathan, chief of special services for the department, said the two were fired because Buck, who became health secretary in February 1979, "wanted new management in the mental retardation administration."

"He wanted more clearly defined goals," Nathan said. "He wanted better management of the program."

On July 1, Nathan said, the mental retardation administration's budget will be increased by $3.5 million to $6.5 million to finance a variety of new and improved programs and services. He said Buck was anxious to have a new management team on board by then.

Nathan said the dismissals were not in response to complaints about conditions at Great Oaks, the second largest residential facility for the mentally retarded in Maryland.

"We have confidence in Cliff Lockyer (the Great Oaks administrator)," said Nathan.

Carl Storm, an official with the Maryland Association for Retarded Citizens called the firings "long overdue."

"The department was very poorly run," Storm said. "The way they administered the department contributed to problems at places like Great Oaks. They need to get someone who is good at bringing different ideas and concepts together. Those men tended to think in compartments."

Among the problems, officials have said, are shortages of trained staff members and programs and low staff salaries.

Nathan said Monaghan will be replaced on an acting basis by Bernard A. Carpenter Jr., currently director of the Department of Health and Mental Hygiene's office of management staff.

Lucas' position will be left vacant pending a reorganization of the department. Both men joined the Maryland department in the fall of 1974. Previously, they had worked on programs for the mentally retarded in New York City.

Lucas and Monaghan did not return a reporter's telephone messages.