Gen. Salah Zeyada, a senior Interior Ministry official on the association’s board, reassured him. “We all agree, brothers, that there will be no security provided for headquarters of the Muslim Brotherhood,” he said.

The police association made no secret of its disaffection: it posted a video clip of the exchange on its Facebook page, and activists opposed to the Brotherhood have cited it as encouragement.

Iconic faces of the Mubarak government have emerged to fan the flames. Hussein Kamel, the right hand of the former spy chief Omar Suleiman, stood behind Mr. Suleiman when he was forced to hand over power on Mr. Mubarak’s behalf. On Tuesday, Mr. Kamel held a news conference to allege nefarious intrigue by the Brotherhood and urge the public to demonstrate on Sunday for Mr. Morsi’s ouster. “We will consider it a referendum,” he declared, to show “the utter failure for the leadership of the Muslim Brotherhood.”

The military, which ruled Egypt for more than a year after Mr. Mubarak’s ouster, retains substantial autonomy under the new Constitution, and the generals have been conspicuously coy about the strength of their allegiance to Mr. Morsi. Last week the military issued a cryptic statement urging all sides to reconcile, pledging to step into politics if needed to protect the nation and making no reference to Mr. Morsi.

To some Brotherhood opponents, “the army seemed to be saying, ‘We will intervene if the violence gets out of hand,’ so there is almost an incentive to do it,” said Nathan J. Brown, a political scientist at George Washington University who was in Egypt at the time.

During a presidential address last week, Gen. Abdul Fattah el-Sisi, the defense minister, sat stone-faced, even as Mr. Morsi saluted the “men of gold” in the Egyptian armed forces. And leftist opposition leaders have come close to overtly welcoming a form of military coup. Hamdeen Sabahi, a former leftist presidential candidate, recently described plans for a post-Morsi government.

“What’s proposed is for the Egyptian people with the help of its military and judiciary to create a formula that would manage this transition,” he said.