BAGHDAD, Iraq — Frequent deadly attacks by insurgents sapped morale and raised combat stress in a U.S. Army unit that included soldiers accused of raping and murdering a 14-year-old Iraqi girl, a private testified at a military hearing yesterday.

Private First Class Justin Cross recounted the “mentally draining” living conditions of the unit in the third day of the hearing to determine if five American soldiers will be court-martialed for the March 12 assault near Mahmoudiya. The girl’s parents and sister were also slain.

“It drives you nuts. You feel like every step you might get blown up. You just hit a point where you’re like, ‘If I die today, I die.’ You’re just walking a death walk,” Private Cross told the hearing.

He said soldiers often drank Iraqi whiskey and took painkillers to relieve the stress of not knowing whether the day would be their last. One such drinking session preceded the rape and murders, the hearing was told by another witness on Monday.

Specialist James Barker, Sergeant Paul Cortez, Private First Class Jesse Spielman, and Private First Class Bryan Howard are accused of rape and murder. If convicted by a court-martial, they could face the death penalty.

Another soldier, Sergeant Anthony Yribe, is accused of failing to report the attack but is not alleged to have been a direct participant.

Yesterday, lawyers for the four main accused demanded a new hearing, accusing Sergeant Yribe’s counsel of deliberately asking incriminating questions.

A former private first class, Steven Green, was discharged from the Army for a “personality disorder” after the incident and was arrested in North Carolina in June on rape and murder charges. He has pleaded not guilty in federal court and is being held without bond.

Combat stress is likely to be the foundation of the defense. All are assigned to the 101st Airborne Division from Fort Campbell, Ky.

Mahmoudiya, about 20 miles south of Baghdad, is one of the most dangerous places in Iraq, where bomb and gun attacks by insurgents take place almost daily.

Under cross-examination by defense attorneys, Private Cross said the unit was “full of despair,” and he himself felt he would die at a checkpoint before he could go home. While on patrol, soldiers constantly feared for their lives, he said.

“I couldn’t sleep, mainly for fear we would be attacked,” Private Cross said. He said the loss of two soldiers shot at a checkpoint “pretty much crushed the platoon.”

The unit went on long rotations through the checkpoints, sometimes spending as much as several weeks without hot food, showers, and contact with family and friends back home, Private Cross said.

Yesterday, another soldier, Private First Class Justin Watt, testified that he heard Mr. Green say, “I want to kill and hurt a lot of Iraqis.”

“I feared for my safety at the TCP [traffic control point],” Private Watt said. “It’s like this, I find out that guys in my squad, guys I trusted with my life, are allegedly responsible for one of the most brutal rapes/murders I’ve ever seen. And everyone has a weapon and grenades.”

An Army criminal investigator, Benjamin Bierce, testified about a sworn statement by Specialist Barker, in which he confessed that he, Sergeant Cortez, and Mr. Green took turns raping Abeer Qassim Hamza al-Janabi, 14.

Specialist Barker also claims in his testimony that Mr. Green killed Abeer, her parents, and their younger, 5-year-old daughter.

Private Cross testified that Specialist Barker — who arranged for the Iraqi whiskey to be delivered through an Iraqi soldier — drank the most, although everyone in the unit had been sipping from the bottle, against military rules. He said he knew Mr. Green also was taking painkillers, even though he never saw Mr. Green do so.

“Everybody was very depressed. It was outlet to release,” Private Cross said.

The defense attorney, Captain Megan Shaw, asked whether all the soldiers were involved in the murders, or if it was entirely Mr. Green’s doing.

Private Cross replied: “Green does nothing by himself.”

Defense attorneys also questioned the interrogation tactics of investigators when they recorded the testimony of the accused. They honed in on clerical errors, such as misspellings of names and absent signatures, to question the legitimacy of sworn statements.

The case has bolstered allegations of misconduct by soldiers, including illegal killings, beatings, and inhumane treatment.

The allegations have increased the mistrust and resentment among Iraqis of American troops and increased calls for their withdrawal.

Since the case became public last month, American officials have said they were concerned it could strain relations with Iraq’s new government if Iraqis perceive that the soldiers receive lenient treatment.

They have offered assurances that the case will be pursued vigorously and that the soldiers will be punished if convicted.

The case has already increased demands for changes in an agreement that exempts American soldiers from prosecution in Iraqi courts.

Prime Minister al-Maliki has demanded an independent investigation.