WASHINGTON, Jan. 16 - The top American commander in Iraq has ordered a criminal investigation into allegations that detainees at the sprawling Abu Ghraib prison outside Baghdad have been abused by American forces, military officials said Friday.

A statement by the military command in Baghdad gave no details about the scope or severity of the incidents, saying only that Lt. Gen. Ricardo S. Sanchez, the senior American officer in Iraq, had directed an inquiry into the latest in a string of reported abuses of prisoners.

"The release of specific information concerning the incidents could hinder the investigation, which is in its early stages," the statement said.

A senior Pentagon official said authorities had been alerted to the possible abuse of detainees in the past few days and were taking the allegations "very seriously."

The American-led occupation is holding thousands of suspected insurgents and criminals at Abu Ghraib, a large prison west of Baghdad that was notorious during the rule of Saddam Hussein for overcrowded cells and torture chambers.

The inquiry ordered by General Sanchez is expected to add fuel to allegations by Amnesty International and many former detainees that the American captors have treated prisoners harshly or abused them in certain cases.

Earlier this month, three Army reservists were discharged for abusing prisoners at Camp Bucca, a detention center near Basra, in southern Iraq. In late December, Brig. Gen. Ennis Whitehead III determined that the three soldiers had kicked and punched prisoners or encouraged others to do so.

Late last year, Lt. Col. Allen B. West, a battalion commander in the Fourth Infantry Division, was allowed to resign from the Army after he fired a pistol near a suspected supporter of insurgents during an interrogation in August to frighten him into giving up information about impending attacks against allied soldiers near Tikrit. Colonel West has defended his actions as necessary to protect his troops.

In addition, the Marine Corps has charged eight Marine reservists in the death of an Iraqi prisoner near Nasiriya last June. Two of the eight marines face charges of negligent homicide, while others face lesser charges, Marine officials said.