He argued that the police and security forces were upset at being blamed for what they considered an essentially political battle that was not of their making. “How is it my fault?” Mr. Heblawi asked, speaking rhetorically on behalf of the police. “Why would I continue to strike against the people and the people continue to strike against me?”

Advisers to Mr. Morsi argue that he is trying to overhaul the Interior Ministry just as he promised. But he is doing it gradually and quietly, they say, in part because he so desperately needs an effective security force to maintain order and to protect the presidential palace, Parliament and the offices of his political party from protesters using rocks and firebombs.

Under Mr. Mubarak, there were almost no major political protests to handle and scarcely any vocal public criticism of the security police. Rights groups say excessive force and even torture by the police have remained common since Mr. Mubarak’s ouster.

On Thursday, the Egyptian state news media reported that a top government authority on forensic medicine had found evidence of torture in the death last month of a celebrated political activist, Mohamed El-Gindy. Contradicting earlier official police statements about a car accident and hinting at a cover-up, the forensic official said a panel had concluded that Mr. Gindy died of a brain hemorrhage consistent with a beating but not a collision. His body turned up in a police hospital, but it was unclear who killed him.

At the Qasr al-Nile police station in Cairo, a large station usually charged with protecting the American Embassy and its neighborhood, about two dozen striking police officers said they had shut down the station in part because one of their colleagues had been killed in clashes with protesters. “Now it happens every day that a police officer is killed somewhere, and there is not enough deterrence,” one officer said, speaking, like all his peers, on condition of anonymity.

Sitting in chairs on the pavement blocking the gate to the station, the officers complained that since the revolution they have been called upon to confront protesters but at the same time demonized whenever they hurt or killed one. They appeared completely unprepared for the policing challenge. “What am I supposed to do, invite them inside and tell them not to be late?” another said.