Bernard D. Crooke Jr. was sworn in as Montgomery County's new police chief yesterday at an event shaped to fit his retiring personality.

At the end of the brief ceremony attended by a dozen people, he seemed embarrassed by the high praise and left the room muttering, "Now we can get down to work."

"I would have loved to hold a big thing in the police academy," said a special assistant to County Executive Charles W. Gilchrist. "But he didn't want it. He wanted it low key. That's the way he is."

Crooke, 45, who spent 23 years in the District of Columbia Police Department, is described as a quiet, popular office. He worked his way up from patrolman to deputy chief in the District, and Crooke says he wants to "earn" the respect of Montgomery's 740-member force.

Crooke's low-key approach, modest goals and-above all-his caution are in marked contrast to his predecessor, Robert J. diGrazia. Hired from outside the force, diGrazia antagonized many policemen with his flamboyant manner and his attempts at reforming the department. diGrazia was fired in December for saying that police view the public as the enemy.

"After two years of the diGrazia fiasco," said an editorial in Roll Call, the newspaper of the county's police association, "morale was at an all time low."

"When diGrazia was here, there seemed to be 1001 issues," said Charles Maier, the county information officer. "The police were always unhappy about something. Now, things have calmed down."

For the past two weeks, Crooke has appeared to be working to show his subordinates that he is on their side.

He has spoken to police groups, saying he favors their goal of retirement with benefits after 20 years. He has met with county officials to work on a minority recruitment plan. By backing the promotion yesterday of two top-ranking police officers-the first such promotions in two years-he showed many of the officers that he takes exception to diGrazia's belief that the department is too topheavy.

It is not just the police department he has tried to reassure. He told the local press association that he views both the press and the police as "necessary evils."

But he avoids making promises or stating specific goals, saying he needs time to learn the problems.

"I'm not going to go out there to make trouble," he said.

Crooke had said his first official act would be "arriving at work on time." Shortly before 8 a.m., on his first day yesterday, Crooke, his wife, and four children were crowded into the office of Maj. Donald Brooks, the acting chief since diGrazia's departure in December. Many credit Brooks, one of the two men to be promoted yesterday, with restoring the department to normalcy.

"Everything's cleaned out, except some internal affairs files," Brooks said.

Most of the day was spent "with trivial paperwork," to make the transition official. He visited the Wheaton station house (where one officer called him "a down-to-earth guy"), and he met with the commanders of four county police districts, telling them, he said later, "that basically I haven't made any decision yet."

At a police awards ceremony, Crooke waited until the winners were alone and away from a crowd to personally congratulate them.

A woman sidled up to him, offering congratulations and saying she was glad to see "positive news" about the police again. "It's a welcome change," she said.

Then she scrutinized the bespectacled middle-aged man, in his off-white, three-piece suit and flashy brown tie. "You ought to get a uniform, though," she said.

"We're working on it," he answered, smiling."Piecemeal."