Lawmakers berated US military chiefs on Tuesday over a sexual assault "plague" in the ranks, but the top brass argued against plans to strip commanders of authority over criminal cases.
A rise in rapes -- along with a spate of high-profile scandals in recent weeks -- has put military leaders on the defensive.
"You need to do more and you need to do it much faster," Senator Mark Udall told the chiefs at a packed hearing of the Senate Armed Services Committee.
The top officers, who made an unusual joint appearance before the panel, seemed intent on heading off proposals in Congress that would alter legal traditions the military holds dear, including rules that allow commanders to decide if a case should go to trial.
While vowing to stamp out the "cancer" of sexual assaults, the generals cautioned against taking sexual assaults and other cases out of the hands of commanders.
"I understand the credibility of the armed forces, the credibility of the army are at stake," said General Ray Odierno, the Army's chief of staff.
"But we cannot simply legislate our way out of this problem."
Several lawmakers rejected the chiefs' stance, saying fundamental changes were needed to open the way to more prosecutions of sexual predators.
Senator Claire McCaskill of Missouri sharply criticized the four-star generals, saying the military misunderstood the problem -- lumping together rape and other crimes with sexual harassment at the work place.
"This isn't about sex. It's about assaultive domination and violence," she said.
The force needs to better document sex crimes, ramp up prosecutions and make it easier for rape victims to come forward, she said.
Sexual assault victims in the American military are "afraid to report" the crime, said Senator Kirsten Gillibrand of New York.
"They think their careers will be over. They fear retaliation. They fear being blamed," she said.
The Democrat is pushing for a bill that would have military prosecutors decide whether a sexual assault or other criminal case should go to trial instead of a unit commander, who she said could lack impartiality.
Gillibrand argued that other countries, including some European allies and Israel, have made similar changes to their own military legal codes with successful results.
But General Martin Dempsey, the military's top-ranking officer, said restricting a commander too severely could undermine an officer's ability to ensure discipline and order in a unit.
"Our goal should be to hold commanders more accountable, not render them less able to help us correct this crisis," he said.
The spike in sexual assault cases is so alarming that Republican Senator John McCain, a decorated veteran, told the generals he had recently told a mother he could not give "unqualified support" for her daughter's decision to join the military.
"I cannot overstate my disgust and disappointment over the continued reports of sexual misconduct in our military," McCain said.
The commandant of the US Marine Corps, General James Amos, and other chiefs acknowledged the military had failed to see the issue as a top priority in years past but now were seized with the issue.
"We hear you loud and clear," Amos said.
Defense Secretary Chuck Hagel, who has called the sexual assaults a "scourge," has suggested amending the military's code to prohibit commanders from tossing out verdicts after a trial.
Although Hagel initially opposed more far-reaching proposals, he has since said he is open to discussing all options.
The service chiefs said the problem ultimately could only be solved by commanders across the force, who were best placed to transform the military's culture.
The chairman of the committee, Senator Carl Levin, agreed that legislation alone could only provide a partial solution.
"We cannot successfully address this problem without a culture change throughout the military," Levin said.
"Discipline is the heart of the military culture, and trust is its soul. The plague of sexual assault erodes both the heart and the soul."