Sliding easily from the Boston-area lecture circuit into its Washington-area counterpart, Montgomery County's new police chief, Robert diGrazia, took to the podium at a Harvard Club luncheon last week to decry the way the city policeman's role is misinterpreted by the public, television, and the policemen themselves.

"The public places what are often impossible demands upon the police. The police are expected to 'control' crime . . . to have a policeman on a citizen's doorstep within minutes of a call for service . . . to be continually visible," diGrazia told a crowd of about 50 at the downtown University Club.

"The public views the police as crime fighters and fails to recognize the other time-consuming demands we face," he added.

"The public perception of the police as only crime fighters has served to reinforce this misconception even among the police themselves."

In order to rectify the misunderstanding, he said, police departments must work to be more open with the public, and must recognize the complexity of police work themselves. And the public, he added, must stop taking its impressions of police work from such television shows as "Starsky and Hutch." "Columbo" and "Adam-12" and pay more attention to police life as depicted in a show like "Barney Miller."

"A typical . . . police officer . . . spends only 20 per cent of his time 'fighting crime,'" diGrazia said. "A police officer . . . assist people wiht a variety of problems on a 24-hour basis."

Instead of perpetuating the hand-gun-wielding, rough-and-ready "Blue Knight" image, diGrazia said, police and the public should realize that there are four main components to a policeman's job besides traffic control.

The protection of constitutional rights. "Whether it's the right of 50,000 people to peacefully assemble or the right of one man to stand on a soapbox and speak his piece, the police must assume the responsibility to protect those rights."

Crime-fighting. "Police officers often blame themselves for the rising crime rate . . . Yet police impact on certain crime is limited at best and nonexistent in many cases . . . In about 70 per cent of murders, the victim knew his assailant. Very few people are killed just walking down the street by a stranger . . . We often arrest those involved, but we very seldom prevent the crime."

Maintenance of order. "This consumes a particularly large amount of the police officer's time. The police are continually called to intervene in family fights, neighborhood disturbances, gang conflicts, and a multitudeof minor disputes. The number of conflicts in an urban congested community are immense."

Aiding the sick and injured. "Whether it be the provision of first aid at the scene of an accident or fire or the care of drunks and drug addicts, it is police officers who are called on to perform this unpleasant task."

Wearing the perpetually-present replica of a pig in his lapel (standing for "Pride, Integrity and Guts," he has often repeated) diGrazia also chastized the police of other eras for demanding that excessive secrecy surround their work.

"The public has come to beleive that there is something sinister going on behind police to the light of day."

In addition, in response to a question about the use of drugs and alcohol in county schools, diGrazia laced into parents who "have not paid attention to their young - and at the same time they're giving them a car for each foot."