The Iraqi government said the arrests had been prompted by a tip from Libya’s transitional government that said documents revealed Col. Muammar el-Qaddafi was working with insurgents to stage a coup. Mr. Maliki has denied any sectarian or political motives behind the sweep, pointing out that both Shiites and Sunnis were arrested. In an interview with Iraq’s official television channel, he said the raids had captured loyalists to Saddam Hussein who were conspiring with Al Qaeda, not peaceful, low-level party apparatchiks.

“We do not have space in our government for those plotting against our government,” he said.

A person briefed on the raid by Iraqi security forces said some of the detainees were in fact military and intelligence officials from the old government. Other names on the target lists, however, included laborers, political adversaries of the government, the elderly — even dead people.

“It’s highly unlikely to be much validity behind” the coup plot, said a Western official who spoke on the condition of anonymity, to avoid upsetting relations with the Iraqi government. “Baathism here is a symbol that Maliki uses as a bogyman. It gives them the leeway to go around arresting people. It’s about a climate of fear.”

Mr. Maliki’s signal achievement since he first won office in 2006 has been consolidating control of the security forces, reducing violence through a willingness to crack down on Shiite militias from strongholds in the southern city of Basra. The defeat of the militias demonstrated to Iraqis, particularly the Sunnis, that Mr. Maliki would evenly target all insurgent groups, regardless of sect, and bolstered his credentials as a nationalist.

As Iraq’s commander in chief, he sometimes micromanages the forces under his control. He pays informers out of his own pocket for intelligence and sometimes sends orders to commanders in the field by text message, officials say.

But in a country where political leaders regularly fly off to second homes in Jordan or London, Mr. Maliki often works through the night in his Baghdad offices and has a steel-trap memory for dates, names and conversations. His family — wife, four daughters and a son — all live in Iraq, while many leading politicians have moved their families abroad.

If he eschews a cult of personality like that built by Mr. Hussein, his close control over Iraq’s police and army and his influence over the country’s judicial system have drawn calls that Mr. Maliki is becoming too powerful.