If it hadn't been for an alert witness with a videocam, the infamous police beating in Los Angeles might never have come to light. That adds weight to the already strong argument for expanding civilian oversight of big city police departments.

Most departments now acknowledge the need to deal credibly with civilian complaints. In New York City - where five officers are charged with murdering a suspect in their custody - civilian complaints are reviewed by a board of six police officials and six outsiders. Los Angeles handles brutality cases within its department, but a board of police commissioners appointed by the mayor has substantial authority to supervise and investigate police policy and management.Still, the powers of such panels are limited. New York's may only advise the police commissioner on discipline and lacks the power to hold public hearings or subpoena witnesses. The Los Angeles panel is barred from investigating individual brutality cases, and its inquiries on policy are hampered by a small staff.

Then why not beef up such groups, and give them authority to discipline individual officers?

Police vehemently resist that idea. . . . Still, when brutality is mishandled, public faith in the police suffers grievously. That's too important to leave wholly to the department, or to the discretion of editors and prosecutors. Furthermore, it shouldn't be all that difficult to create a review panel capable of reassuring the public while respecting the needs of police.

The panel would leave routine complaints to the department's internal investigation units. But in major brutality cases, when investigations by the department or district attorney leave unanswered questions, the panel would conduct its own inquiry, subpoenaing witnesses and holding hearings. It need not intrude directly on the department's discipline procedures as long as it could conduct serious inquiries and publicize the results.

The panel would also monitor overall performance of the department, issuing regular reports and suggesting ways to improve procedures for handling misconduct. It might also intervene with hearings and recommendations when it spotted patterns of abuse in particular kinds of cases, or even by particular officers.

Properly led, the panel need not trespass on commanders' authority or demoralize officers on the beat. But the very existence of such a group could influence police behavior. And it would do much to protect the public trust on which society, and the police, depend.