Fairfax County's new police chief said yesterday he will aggressively recruit minority officers, possibly paying them bonuses, as he works to curb gang violence and reach out to new immigrants.

"We need a more diverse force across the spectrum," David M. Rohrer said in an interview on his first day on the job, "from the first phone call the officer takes when someone reports a crime, to who writes the report, to the detective who interviews a suspect."

In 23 years on the Fairfax force -- rising from rookie patrol officer to commander of special operations to station commander and deputy chief -- Rohrer, 47, has seen the county of 1 million-plus remake itself from sleepy suburb to United Nations of newcomers and dense population center whose traffic tries the most patient driver. Now, with his appointment to the top job by the Board of Supervisors this week, the new chief begins his own transformation, from unassuming introvert to high-profile leader of Virginia's largest local police force.

"That's going to be my role. I accept that. But it's not my forte," Rohrer said with a grin.

Fellow officers and county supervisors described Rohrer, who beat out three internal finalists and one outsider, as someone who could easily be underestimated because of his economy of words. He was not immediately the leading candidate for chief during the board's five-month search.

"He's not real demonstrative or animated," said Supervisor Michael R. Frey (R-Sully), who met Rohrer when he was commander of the Fair Oaks police station in Frey's fast-growing western Fairfax district. "He's quiet and low-key. But he's very thorough. And he has very sound judgment."

It was Rohrer's experience with so many aspects of policing, from high-risk hostage cases to overseeing Fairfax's role in the sniper case investigation in 2002 that drew board members to his corner, they said. And that resume also gives him more credibility with patrol officers, colleagues said.

Rohrer counts his seven years with the special operations team, apprehending rapists and responding to other high-profile crimes, as the best years of his career.

"He's not a pubic relations person, he's a cop, and the troops love him," said Janet Patrick, chairman of the Citizens Advisory Council, a liaison with the police department. "He's not just sitting up in his 11th-floor office in the Massey Building. He bleeds with the line cop."

Rohrer's personal style cuts a striking contrast with that of his predecessor, J. Thomas Manger, who retired in January to take the chief's job in Montgomery County. Where the charismatic Manger had been a local cable TV anchorman and actor in community theater, Rohrer says he's happiest reading biographies, leading a Boy Scout troop and hiking or scuba diving with his wife, Ellen, and two teenagers. If he has a hero, it's Abraham Lincoln, "because of his ability to drill down to issues," he said.

Rather than micromanage, Rohrer tends to trust those under his supervision, colleagues said.

"He values the officers' opinions," said Capt. Larry Moser, commander of the Mount Vernon station and Manger's chief of staff.

Even though Rohrer is chief in a traditionally low-crime county, his department faces a public increasingly alarmed by a surge in gang violence and agitated by traffic congestion and auto accidents. About 60 people have died in car accidents, many of them teenagers, in each of the past few years, Rohrer said. "It's not just enforcement we need, but voluntary compliance" with rules of the road, he said. "We need to keep getting the message out" about safe driving.

He said he will fight for Fairfax's share of resources to make sure the county is prepared for a terrorist attack. But finding strategies to stop teenagers from joining gangs could be his biggest challenge, as violence continues.

"I think we're doing a lot now, with the schools, with the police in the schools," he said. "But we need more programs for our young people. We need to find things for kids to do."

More and more, in some communities, officers are assuming roles that include social work. Nowhere is this more visible than in neighborhoods of newcomers, where many immigrants, who hail from countries where police are feared, are afraid to report crimes when they have been victims, Rohrer said.

"Language barriers have added a whole new layer of complexity," he said. "I'm very concerned that we aren't learning about all the crimes that are occurring."

To change that, he is insistent that the department hire more Asian, black and Hispanic officers. Hispanics represent 4 percent and Asians 2.5 percent of the force of 1,340 sworn officers. Blacks make up 8.6 percent. Fairfax, in the shadow of the federal government, competes to recruit and keep those officers, but often loses out, Rohrer said. Higher salaries for officers with language skills could be one incentive, he said and added that he plans to expand an existing cadet program for high school graduates.

"When he says he's committed to increasing the diversity of the force, he means it," said Frank Kitzerow, who served as commander of criminal investigations under Rohrer and is now police chief in Portsmouth, Va. "Don't let that unassuming personality fool you for a moment."

In 23 years on the Fairfax force, David M. Rohrer rose from patrol officer to deputy chief to chief.