The promotions of two veteran Montgomery County police officials, made at the same time an outsider was chosen over them as chief, has become a subject of debate because of the county's strict rules on police promotions.

Majors Donald Brooks and Wayne Brown were bothe promoted to the rank of lieutenant colonel on May 1, the same day Bernard D. Crooke, an assistant chief on the D.C. police force, was installed as chief. County officials say those promotions may have violated regulations.

Police department sources contend that the two men were given the promotions and the accompanying $5,000-a-year raise in order to keep them from retiring. Both men now make $49,160. Brooks, who was acting chief until Crooke was named, actually took a $100 a year cut from his salary as acting chief, but he would have taken a $5,000 cut if he had become a major again.

County merit system rules require that any vacancy be advertised before it is filled and that candidates be given a reasonable opportunity to apply for the opening.

Although county personnel board executive secretary Jerry Moser said yesterday the board has taken no formal action on the promotions, he did say the board has asked the county personnel department to "formally tell us exactly what action was taken." He said once that answer is received the board will decide what to do next.

County administrative officer Robert Wilson and Crooke are scheduled to meet this morning to discuss the problem. Wilson sent members of County Executive Charles W. Gilchrist's staff a memo yesterday morning telling them he had learned that the personnel board intends to investigate the legality of the promotions and will not deal with other police promotions until the matter is cleared up. It was Gilchrist who promoted the two majors.

The personnel board cannot take formal action until a written complaint is filed and Moser said yesterday that no such complaint has been received.

The police department has not had a lieutenant colonel since 1977 when the post was vacated and then chief Robert J. diGrazia abolished the rank. The department also must decide whether to fill the two vacancies in the major rank left by the two promotions.