The document is expected to be drafted in a rush and submitted to a referendum on the eve of the presidential election, by the end of June, while the military council is still in power. The council has repeatedly sought to use its control of the interim government to influence the drafting of the constitution in order to preserve special powers and privileges even after the election of civilian leaders.

In recent months, Mr. ElBaradei has repeatedly attacked the council for the brutality of its crackdown on protesters demanding an end to military rule; soldiers and security police officers have killed more than 80 demonstrators since early October. In his statement on Saturday, Mr. ElBaradei also blasted what he called the inept stewardship of the interim government. “The randomness and the mismanagement of the transitional period are pushing the country away from the aims of the revolution,” he said.

But Mr. ElBaradei also said that he would continue to agitate for democratic change, continuing the catalytic role he has played since he returned home to a hero’s welcome at the Cairo airport in February 2010.

Mr. ElBaradei declared then that he would challenge Mr. Mubarak for president if the rules were changed to allow fair elections, a provocative gesture that was considered hopeless at the time, but challenging enough to land a less prominent figure in prison.

He helped found an umbrella group, the National Association for Change, which became a rallying point for many of the young activists who later helped lead the uprising against Mr. Mubarak.

Mr. ElBaradei appears to have been one of the few who publicly anticipated the revolt that forced out Mr. Mubarak. In a widely circulated online video he released weeks before the revolts broke out in Tunisia and then Egypt, Mr. ElBaradei bluntly told the Mubarak government that it faced its “last chance,” predicting “there will be violence.”

“A day of reckoning will come,” he said. “And I am asking the Egyptian people to keep a record of every case of torture and oppression and the violation of personal liberty.”

In an interview in December 2010, about a month before the uprising began, he repeatedly invoked his visits to the Tehran Hilton on the eve of the Iranian revolution in 1979. “Things were boiling underground, and that is what I see here in Egypt,” he said. “I would not be surprised if you saw violence in a couple of weeks, or in a month or two.”