Cambridge Mayor Walter J. Sullivan denied yesterday charges of racial discrimination in police hiring and promoting practices.

His response came in the wake of a pending suit brought by five black patrolmen, who accuse city officials of not appointing black sergeants and failing to recruit more blacks into the police force.

The suit, scheduled to be heard in U.S. District Court after Labor Day, names the mayor, the city council, the police chief and civil service commissioners as defendents.

Sullivan said, "According to law, we're not discriminating against anybody."

State law requires sergeants to be chosen from a ranked list of names provided by the civil service department and based on test score results.

The police department is seeking to appoint only nine sergeants, ruling out the possibility of promoting the highest ranking black, who scored 20th out of 110 patrolmen who took the exam in April.

The patrolmen's suit states that because of Cambridge's rising black population and increasing number of racial incidents, a black sergeant would uniquely serve the needs of the community.

There has been one black sergeant in the history of the police force. The five patrolmen who brought the suit are currently the only permanent black members of the 250-man department.

Sullivan denied the patrolmen's charges that the police do not actively recruit blacks. He said, "When I was mayor in '68, we gave them the opportunity. We provided programs for those minority people, but they never went through with them."