The staff director of the D.C. City Council Judiciary Committee, who was arrested by city police on an assault charge late Wednesday night, asked the D.C. Police Chief Burtell M. Jefferson yesterday to investigate the conduct of the officers involved in the arrest.

Gregory E. Mize, 33, chief staff clerk of the committee that oversees the operation of the Police Department, made the request in a letter to Jefferson.

Mize charged that the officers, who were operating in a radar speed trap at 16th and Nicholson streets NW just north of Carter Barron, had used unnecessary force on him. He also said the arresting officer switched to a more serious charge against him after Mize said he would contest a lesser charge of disorderly conduct initially filed against him.

Police officials and Mize have given different versions of the incident.

Mize who had walked from his home nearby to the intersection, was arrested after he intervened while police were arresting two motorists. One did not have a driver's license, and the second was disorderly, police said. Mize said the second man had been yelling at the officer and that Mize asked if he were being arrested for "mouthing off."

Mize said the policeman told him to move on but that Mize attempted to say something else and was grabbed by another officer who choked him and placed him in the police wagon.

The police account said Mize refused to step away from the officers and pushed one of them before he was arrested.

Councilman David A. Clarke (D-Ward 1), chairman of the Judiciary Committee, and who is Mize's boss, said yesterday that he was disturbed by mize's account, particularly the change in charges.

Clarke said government officials should be treated "no worse or better" than anyone else, but that in this case, "it appears that he got something worse."

Mize denied earlier accounts that he had demanded that police drop the charges against him. He also said he did not mention Clarke's name until police asked him for a personal reference other than a family member.

A hearing on the charge has been set for July 16.