Montgomery County Police Chief J. Thomas Manger will retire in April after 15 years running the 1,300-officer force during which he became a national voice on police issues.

Manger, who announced his retirement Wednesday, said he plans to join the Major Cities Chiefs Association to head the group’s legislative efforts in Washington.

His departure follows the Dec. 3 swearing-in of Marc Elrich (D) as county executive, the first change in the county’s top political job in 12 years.

Manger, 64, has been a police officer for 42 years and is a well-known figure in the Washington region, having led the Fairfax County force in Virginia before taking the Montgomery job.

Manger said Elrich has asked for his help in selecting a new chief, who would need County Council approval. In an interview Wednesday, Manger praised possible in-house candidates.

“I think we’ve got great people to choose from who are here,” he said, citing as examples Assistant Chief Laura Lanham, who directs the patrol bureau, and Assistant Chief Marcus Jones, who directs the investigation services bureau.

Under the glass surface on his desk, Manger keeps sketched tracings of the names of officers who died in the line of duty under his command. Those losses, he said, have been the most difficult of his job.

“They’re in my heart, in my head,” he said.

He said he also carries the painful memories of homicide victims, particularly children. “You personalize these things,” he said.

Elrich said he is planning a national search for Manger’s successor but is open to promoting from within.

“There may be a couple of good candidates within the department, but we absolutely want to give ourselves some leeway to see who else might be interested in this,” he said.

Elrich said he wanted to keep Manger on in his new administration, and that the two worked well together over the years. Elrich, a former county council member, had been chair of the council’s Public Safety Committee.

“I’ve worked with him a lot. We’ve basically been on board on the same playbook for a very long time,” he said. Elrich said Manger’s announcement “is a bittersweet day” for the county.

Manger was the 16th police chief in the 97-year history of the department, according to county officials. He was sworn in Jan. 30, 2004. He will become the second-longest-serving police chief, behind James S. McAuliffe, who served from 1955 until 1971, according to county officials.

Of his tenure, Manger said he was particularly proud of reducing crime even as the county’s population grew and of bolstering trust between the department and the community.

“We were able to get a fair amount accomplished there,” he said of the trust-building. “Montgomery County has a very demanding public. They have high expectations.”

In a statement Wednesday, the county’s police union, the Fraternal Order of Police Lodge 35, praised Manger’s efforts to improve drunk-driving laws in Maryland and to resurrect the county’s police cadet program.

But it also said in a statement that “unfortunately, while serving as the director of the police department, Tom Manger was often unwilling to cooperatively work with FOP Lodge 35 to accomplish more,” and that it looked forward to a new chief “willing to work collaboratively.”

Whoever follows Manger will face the job of policing a county of 1.1 million people, with agricultural regions in the north, growing suburbs, and more densely populated urbanized areas such as downtown Silver Spring. The majority-minority county has a per-capita income among the highest in the state, but also areas of poverty. A third of its residents are foreign-born, with its school district teaching students from more than 157 countries, making the county one of varied policing challenges and opportunities.

Manger walked a careful line to avoid alienating immigrant communities, whose trust the department needs to solve crimes. While he was willing to work with federal immigration police, he stopped short of having his officers do anything that could be seen as enforcing federal immigration laws.

In recent years amid the national outcry about police shootings of civilians, Manger has regularly expressed sharp concern about those deaths, but also frustration over what he has called a false narrative of out-of-control officers.

“Police today are paying for the sins of their fathers and grandfathers,” Manger said Wednesday. “The truth is that police are better trained and more accountable than ever. People who don’t like police have used bad examples to paint with a broad brush. It’s been frustrating for that narrative to gain so much ground — both politically and on the 24-hour news channels.”

As Montgomery’s chief, Manger embraced the use of body-worn cameras for the force, wearing one himself.

“He certainly let people know that he wanted everyone to realize exactly what had happened during a situation. That in itself speaks volumes about him,” said Montgomery County Council Vice President Sidney Katz (D-District 3), who chairs the council’s Public Safety Committee.

He said the timing of Manger’s announcement came as a surprise, but his retirement was not. “He will certainly be someone that will be dramatically missed,” Katz said. Council President Nancy Navarro (D-District 4) said the county under Manger “has become a safer and more welcoming place.”

Chuck Wexler, executive director of the Police Executive Research Forum, said Manger has been an effective advocate in explaining why local police cannot be expected to enforce federal immigration laws.

A tense point for Manger on immigration issues came in 2017, when his detectives charged two Rockville High School students, who were in the country illegally, with first-degree rape after allegations that they sexually assaulted a classmate in a school bathroom stall. The case drew national attention, but fell apart when Montgomery prosecutors dropped the charges after concluding that they would have difficulty proving the allegations in court.

Community members who wanted stronger immigration enforcement, and those who argued that immigrants were being scapegoated, grew angry. “The community was outraged on both sides,” said Wexler, who credited Manger’s leadership for damping down the differences.

Manger, who as chief earned just under $250,000 in 2017, according to county records, said the job shift from chief to chiefs association will allow him to see more of his wife and children, who are 17 and 15.

“It’s a cliche to say that upon retirement you want to spend more time with your family,” he said. “I do want to spend more time with my family. I just hope they want to spend more time with me.”

Manger expressed great fondness for the “hundreds of friendships” he’s made among Montgomery residents he met at community meetings and traveling the county. “That’s a lot for an introvert like me,” Manger said.

Manger grew up in Baltimore and Montgomery County, attended Montgomery Blair High School in Silver Spring and graduated from the University of Maryland. His first law enforcement job was as a “summer cop” in Ocean City. For years, he has been active in the Major Cities Chiefs Association.