Acting Montgomery County Police Chief Donald E. Brooks has decided to keep Dr. Phyllis McDonald as acting head of the police training academy despite the opposition several officers have expressed over having a female civilian supervise the training.

But the decision as to who will become permanent director of the training academy will have to come within 90 days, when McDonald's term as acting director ends, according to Gerald Mozer, the executive secretary of the county Personnel Board.

McDonald's appointment last spring by then chief Robert J. diGrazia, drew an immediate outcry from the officers and resulted in a backlash of criticism toward diGrazia. Last week, County Executive Charles W. Gilchrist fired diGrazia, stating that the ex-chief was "no longer effective" in leading the department.

DiGrazia has said he hired McDonald because of her expertise in personnel matters and because he supported the concept of opening up police departments to more civilians.

Brooks said of his decision to seek an extension of McDonald's term, "This affords me the opportunity to make a valid appraisal of her philosophy and the work of the training staff in their preparation of training programs for the upcoming recruit class and the present officers."

He added that "I still intend to involve officers in the training process."

Brooks also announced several major personnel shifts yesterday.

Maj. Wayne Brown has been made second in command in the department and placed in charge of the day-to-day operation of the department.

Brooks has said he wants to retire within the next six months, at which time Brown, who tried unsuccessfully to become chief in 1976, will be the highest ranking officer in the department.

Brown also announced that Capt. Ronald E. Bowers has been named his executive assistant and will take over the management services bureau, a key division in the department that was headed previously by Philip H. Marks, diGrazia's civilian chief assistant. Mark's authority as a civilian was also widely resented by the officers.

Brooks said Marks will stay on in the department as a "senior management analyst . . . in recognition of his outstanding abilities in such technical areas as the upcoming computer-aided dispatch system and oother projects requiring considerable technical knowledge."