WASHINGTON — Instances of sexual assault among U.S. service members have fallen over the past year, a new report suggested Friday, but Pentagon officials said more work remains to be done on preventing retaliation against those who report abuse.

Defense Secretary Ashton Carter, presenting his department’s assessment of sexual assault for fiscal 2014, said the military had made strides in discouraging abuse across the armed forces.

A Pentagon-commissioned study by the private Rand Corp. found that an estimated 18,900 service members, including 10,400 men and 8,500 women, were subjected to some kind of unwanted sexual contact, a drop of 27 percent from fiscal 2012. Unwanted sexual contact is a term that covers a wide variety of actions.

The Rand assessment, which was based on a survey of service members, also introduced a new measurement for tracking assaults – rather than unwanted sexual contact – which will make it easier to prosecute them. Using this terminology, Rand found that an estimated 20,300 out of a total of 1.3 million service members were victims of sexual assault in 2014.

“That’s clearly far, far too many,” Carter told reporters at the Pentagon. “Even though sexual assault is a disgrace in any form and happens far too often across our country, it’s a particular challenge for us here.”

In 2014, the Pentagon received 6,131 reports of sexual assault, a jump of 11 percent from 2013, a change that officials believe signals improved confidence in the military’s ability to respond properly to such allegations.

Much of the data presented Friday was contained in a December 2014 report to the White House, but this week’s report provides additional details that paint a mixed picture of abuse in the military.

Accounts of widespread assault within the ranks and officials’ failures in holding perpetrators accountable have emerged as a major issue for Pentagon leaders in recent years. Carter, who took office in February, said the military’s ability to learn from mistakes would help it move toward eradicating sexual assault.

For the first time, the annual study examined how male service members experience assault. It found they were more likely to experience repeated abuse by more than one person and were more likely to view the aggression as hazing instead of sexual acts.