CAIRO — President Mohamed Morsi of Egypt forced the retirement on Sunday of his powerful defense minister, the army chief of staff and other senior generals, moving more aggressively than ever before to reclaim political power that the military had seized since the fall of Hosni Mubarak last year.

Mr. Morsi also nullified a constitutional declaration, issued by the military before he took office on June 30, that had gutted the authority of his office. On Sunday, he replaced it with his own declaration, one that gave him broad legislative and executive powers and, potentially, a decisive role in the drafting of Egypt’s still unfinished new constitution.

The maneuvers by Mr. Morsi, a former leader of the Muslim Brotherhood, cemented a major shift in power that began with his election in the face of intense opposition from the military. It received a decisive push this month after 16 Egyptian soldiers were killed in northern Sinai, deeply embarrassing the generals and weakening them politically.

Still, it was unclear on Sunday whether the generals would accept Mr. Morsi’s latest moves. One top general said the reshuffle was made in “consultations” between Mr. Morsi and the military. There was no sign of a backlash by the military on Sunday night, as the president’s supporters held large rallies in Cairo. And other figures from across the political spectrum hailed Mr. Morsi’s decision.