FORT MEADE, Md. — A military judge on Monday dismissed two of the most serious charges against the only officer charged with abusing detainees at Iraq's Abu Ghraib prison after an investigator acknowledged he failed to read the defendant his rights.

Army Lt. Col. Steven L. Jordan is the last of 12 Abu Ghraib defendants to be court-martialed. He still faces four counts, including cruelty and maltreatment of detainees.

His trial was set to begin Monday afternoon.

Jordan, the former director of the prison's interrogation center, was charged after photographs surfaced showing low-ranking U.S. soldiers assaulting and humiliating naked detainees at Abu Ghraib in late 2003 and early 2004. Jordan isn't in any of the pictures, but he is accused of allowing the mistreatment to escalate.

Jordan, 51, of Fredericksburg, Va., has said he is a scapegoat, considered expendable because he is a reservist.

In court Monday morning, the prosecutor, Lt. Col. John P. Tracy, announced that the investigator, Maj. Gen. George Fay, had contacted prosecutors Sunday to say that he "misspoke" when he testified during a pretrial hearing that he advised Jordan of his rights during an interview in 2004.

In that 2004 interview, Jordan had told Fay he never saw detainees being abused and never saw nude detainees.

The judge, Army Col. Stephen R. Henley, granted the government's motion to dismiss two charges that were based on those statements: making a false official statement, punishable by up to five years in prison, and obstruction of justice, punishable by up to three years.

Jordan still is charged with disobeying Fay's order not to discussing the investigation with others. The three other counts refer to the treatment of prisoners. Jordan is charged with failure to obey a regulation, punishable by up to two years in prison; cruelty and maltreatment of detainees, punishable by up to one year; and dereliction of duty, which carries a maximum prison sentence of six months.

Fay interviewed many other soldiers during his investigation. In his report, he concluded that Jordan's tacit approval of violence during a weapons search on Nov. 24, 2003, "set the stage for the abuses that followed for days afterward."

The search, known as the "roundup," followed an episode in which a Syrian detainee fired at Jordan and other soldiers with a handgun he had obtained from Iraqi police officers, according to investigative records.

Jordan's defense, led by Capt. Samuel Spitzberg, contends that although Jordan was the titular head of the interrogation center, he spent most of his time trying to improve soldiers' deplorable living conditions at Abu Ghraib.

The defense argued during an October hearing that interrogation conditions were set by two other officers: Col. Thomas Pappas, an intelligence brigade commander who was the highest-ranking officer at Abu Ghraib, and Capt. Carolyn Wood, leader of a unit within the interrogation center called the Interrogation Command Element.

Neither Pappas nor Wood has been charged with crimes. Pappas was reprimanded and fined $8,000 for once approving the use of dogs during an interrogation without higher approval.

Eleven enlisted soldiers have been convicted of crimes at Abu Ghraib. The longest prison term was given to former Cpl. Charles Graner Jr., of Uniontown, Pa., who was sentenced in January 2005 to 10 years for assault, battery, conspiracy, maltreatment, indecent acts and dereliction of duty.