The reasons for Mr. Sadr’s decision to withdraw from politics were not entirely clear, and members of his party would not comment on the announcement. Ten members of his party in Parliament have announced that they will resign, but it is still uncertain whether other lawmakers or cabinet members will step down.

“I resigned from Parliament as a response to our leader’s call, and will not participate in the coming election,” said one member of Mr. Sadr’s party, Zaineb al-Tai. She offered no further details.

Some Iraqis said they viewed Mr. Sadr’s announcement as a positive development for Iraq, a step toward separating religious from politics, but others said they did not believe Mr. Sadr because he previously ordered members of his party to withdraw from the government, only to reverse his decision a few days later.

“I hope that Moktada sticks to this decision,” said Walled al-Chalabi, 34, a Shiite shop owner in Baghdad. “Usually he changes his mind really soon. I wish that we could get rid of those Islamic politicians, both Sunnis and Shiites, and have a civil state instead, but we still have Maliki and Hakim, who are even worse than him.” Ammar al-Hakim is the leader of another Shiite party, the Islamic Supreme Council of Iraq.