The Prince William County Police Department continues to excel across the board in meeting national criteria for a well-run operation, but it struggles to attract a diverse force, according to a recently released accreditation report.

The Gainesville-based Commission on Accreditation for Law Enforcement Agencies re-accredited the police department and training academy in November, Acting Chief Barry Barnard said.

The agency found that Prince William generally meets or exceeds national standards and criteria, especially in a difficult environment, given the county’s crackdown on illegal immigrants, according to the report.

The department has been accredited by the agency since 1987, and it is re-accredited every three years, officials said.

James E. Carmody, police chief in Wyoming, Mich., led the team assessing Prince William’s department. He could not be reached for comment Friday.

The report found few complaints against the department; there were 13 claims of bias and 13 of excessive force from 2009 to 2011. The low number, given the more than 137,000 contacts with police, is a testament to the department’s professionalism and training, the report said.

“The agency’s continued low crime rate and above-average clearance rate are attributed to the dedication and hard work of both sworn and civilian [police] staff,” the assessment said.

County police close cases that involve robbery, rape, aggravated assault and murder about 70 percent of the time. Property crimes, such as burglaries, are closed about 24 percent of the time, in line with other localities nationally, the report said. Barnard said that although those numbers are comparable for similar communities, the department strives to do better.

The report noted the community’s concern about how the department would enforce Prince William’s anti-illegal immigration policy, which county supervisors adopted in 2008. The policy mandates that police question all criminal suspects who are arrested about their immigration status.

In 2011, 5 percent of the department’s 14,000 arrests involved people who had a questionable immigration status or were in the country illegally, the report said. The department does not track traffic stops by gender or race, and Barnard said he has not seen any reason to do so.

Although the department seeks to recruit minority candidates, it hasn’t been wholly successful. The report said 7 percent of officers are black, 8 percent are Hispanic and 14 percent are women.

Barnard said recruiters seek out minority candidates and travel to diverse areas to attract them.

“We haven’t had the success we need to have. We want to reflect the community, and it’s important . . . because of the nature of the work that we do,” he said. “We need to continue to do everything we can.”

On the whole, Barnard said, the department’s re-accreditation reflects officer’s dedication.

“We’re proud of it,” he said. “We work our tails off to bring professional policing services, and I think this report shows that.”