“Even Saddam Hussein had more legal counsel than I ever had,” said Mr. Vance, who said he planned to sue the former defense secretary, Donald H. Rumsfeld, on grounds that his constitutional rights had been violated. “While we were detained, we wrote a letter to the camp commandant stating that the same democratic ideals we are trying to instill in the fledgling democratic country of Iraq, from simple due process to the Magna Carta, we are absolutely, positively refusing to follow ourselves.”

A spokeswoman for the Pentagon’s detention operations in Iraq, First Lt. Lea Ann Fracasso, said in written answers to questions that the men had been “treated fair and humanely,” and that there was no record of either man complaining about their treatment.

Held as ‘a Threat’

She said officials did not reach Mr. Vance’s contact at the F.B.I. until he had been in custody for three weeks. Even so, she said, officials determined that he “posed a threat” and decided to continue holding him. He was released two months later, Lieutenant Fracasso said, based on a “subsequent re-examination of his case,” and his stated plans to leave Iraq.

Mr. Ertel, 30, a contract manager who knew Mr. Vance from an earlier job in Iraq, was released more quickly.

Mr. Vance went to Iraq in 2004, first to work for a Washington-based company. He later joined a small Baghdad-based security company where, he said, “things started looking weird to me.” He said that the company, which was protecting American reconstruction organizations, had hired guards from a sheik in Basra and that many of them turned out to be members of militias whom the clients did not want around.

Mr. Vance said the company had a growing cache of weapons it was selling to suspicious customers, including a steady flow of officials from the Iraqi Interior Ministry. The ministry had ties to violent militias and death squads. He said he had also witnessed another employee giving American soldiers liquor in exchange for bullets and weapon repairs.

On a visit to Chicago in October 2005, Mr. Vance met twice with an F.B.I. agent who set up a reporting system. Weekly, Mr. Vance phoned the agent from Iraq and sent him e-mail messages. “It was like, ‘Hey, I heard this and I saw this.’ I wanted to help,” Mr. Vance said. A government official familiar with the arrangement confirmed Mr. Vance’s account.