Sixteen black Prince George's County police officers have either resigned from the county Fraternal Order of Police or are in the process of resigning, Cpl. Larry Bowman, a county robbery detective, said yesterday.

Bowman said he has resigned and he and the others who resigned intend to form a new association. They believe the FOP has been inadequate in bringing about improvements in the department's promotion and assignment of black officers, he said, adding that the issue has "been long brewing."

Prince George's is the third Maryland county where black law enforcement officers have raised concerns in the last two months about alleged discriminatory practices. Earlier this summer, black police officers in Montgomery County filed suit against the police department there, claiming the department discriminated against blacks in hiring, training and promotion.

And earlier this month, the Charles County branch of the NAACP asked the Maryland Human Relations Commission to look into alleged discriminatory practices against blacks in the county sheriff's office. Also, 11 black deputies resigned from the Charles County FOP.

Bowman said there are 155 supervisors in the Prince George's police department and only one of those officers is black. "There's no upward mobility," he said.

About 980 officers are on the force, and about 140 of those are black. The first black officers were hired in 1969 and the numbers increased rapidly in the mid 1970s.

"We're having some problems," FOP President Mahlon Curran acknowledged yesterday, ". . . it seems to be promotion-related."

Curran denied that black officers had resigned from the union, but said he would meet with black officers next week to discuss the issues.

Tom Lennon, FOP vice president, said he was aware that black officers are upset about promotions, but, he added, "We have had no promotions since January. . . . It's tough times in Prince George's now."