The head of the group representing Montgomery County's black policemen yesterday said new Police Chief Robert J. diGrazia has shown "no commitment" to promoting black officers and has done little to improve their treatment by superiors.

Detective Anthony Fisher, a member of the Coalition of Black Police Officers, said the group's initial optimism over diGrazia's appointment last November "has changed drastically."

After several introductory meetings, Fisher said DiGrazia "never called us to discuss specific problems . . . Nothing's been initiated."

The group, composed of the 27 black policemen on the 784-member force, yesterday issued a sevenpage memorandum discussing the problems facing blacks in the department.

Fisher said DiGrazia has not shown any interest in placing blacks in policy-making positions, establishing an effective affirmative action program, or examining why 12 of the 17 blacks admitted to last year's police academy class ultimately failed to make the force.

The black's failure rate proves that either the county personnel department, which must pass on new recruits, is "incompetent and did a very poor job" in selecting black applicants, or that the black's supervisors were "imcompetent and racist" the group's statement said.

DiGrazia, who was Boston's police chief for the last four years before taking the Montgomery County post in November, declined comment yesterday. While in Boston, he was credited with significantly increasing the number of blacks and women on the police force.

The black officer's statement is the second such criticism of DiGrazia recently. Last week the 400-member Montgomery County Police Association said DiGrazia was creating "a serious morale problem" by making "derogatory statment" about nonuniformed officers.

The black officers' group agreed with that criticism and also said DeGrazia's stated intentions to cut back on the number of promotions in the department would almost completely shut blacks off from reaching the higher levels of the department.