WHENEVER THE TOP COMMAND of a police force undergoes change -- and it's happening with considerable frequency around the country -- you can expect at least a few complaints from the rank and file. That's what we're hearing as a result of constructive changes announced in two suburban Maryland jurisdictions: the selection of a new chief for Montgomery County, who comes from the District's ranks, and the recruiting by Prince George's County of top officials from outside the department. In each instance, the intention of the county executive is to build more community support for the delicate and difficult work demanded of today's police.

When Montgomery County Executive Charles W. Gilchrist fired Police Chief Robert J. diGrazia, it was plain that there were sound reasons for the dismissal -- even though Mr. diGrazia had worked to improve the department, But his unnecessary bad-mouthing of his force had brought officers -- black and white -- to the point of near-rebellion. So now, Mr. Gilchrist has chosen Bernard D. Crooker Jr., second in command of the Metropolitan Police Department, to be the new chief.

As assistant chief in charge of field operations in the city and as a 23-year veteran of the D.C. force, Mr. Crooke has compiled an impressive record and enjoys a high level of professional respect from black and white officers. Though the presidents of the Police Association and the Fraternal Order of Police have expressed "disappointment" that the selection was not from within the ranks, Chief Crooke is quite familiar with the workings of the force; he is a Washington native who has lived most of his life in Montgomery County and has a high regard for the county department. He also is considered a progressive thinker who can advance many of the better changes effected by Mr. diGrazia, such as the increased use of civilians.

The good news for Prince George's comes in the form of a decision by County Executive Lawrence J. Hogan to recruit top officials from outside the department for the first time in its history -- as part of an effort to bring blacks into the highest levels of the force. Since the department has never hired anything but privates before -- and given the fact that the force is currently 92.8 percent white, with no black officers above the rank of sergeant -- the recruitment effort makes enormous sense. Police Chief John W. Rhoads, who rightly says "it is important that this department be fully integrated," deserves full public support in the attempt to carry out this improvements as fairly and sensitively as possible.