Senior military officials at the Pentagon and officers in command positions in the services have opposed a Senate proposal to strip commanders of the power to decide which sexual-assault complaints are taken forward to trial. (AFP/Getty Images)

The number of military service members who reported that they had been sexually assaulted rose by 8 percent over the past year, according to a new Defense Department report that is sure to add fuel to a debate in Congress over whether the military is effectively prosecuting sex crimes.

Despite the climb, the Pentagon cited progress on a number of fronts in its report, an annual assessment of its efforts to prevent sexual assault.

For instance, on the basis of an anonymous biannual survey of service members, the military estimated that 19,000 troops were victims of “unwanted sexual contact,” a definition that includes a wide variety of offenses. That figure was down sharply from an estimated 26,000 two years ago, but back at roughly the same level that was reported in 2010.

While most sexual-assault victims are apparently still unwilling to come forward, the report found improvement there as well, estimating that 24 percent of victims filed reports with a military authority during the fiscal year that ended Sept. 30, up from 11 percent two years earlier.

The Pentagon has been under pressure to show it has made progress in preventing and prosecuting sex offenses, amid threats by lawmakers to overhaul the military justice system and strip commanders of their power to oversee such cases.

People on both sides of the debate had been awaiting the results of the Pentagon’s report, which Defense Secretary Chuck Hagel is scheduled to unveil Thursday. A copy was obtained in advance by CNN, which posted it online Wednesday night.

Overall, the military received 5,983 sexual-assault reports last year, compared with 5,518 the year before. That came on top of an even sharper increase in 2013, when the Pentagon reported a 50 percent jump that shocked many lawmakers and advocacy groups.

Military leaders and some lawmakers said the rise is not necessarily evidence that crimes have become more prevalent, but rather that victims are more willing to trust the system and file reports.

“Reporting of assaults being up and incidents of assault being down are exactly the combination we’re looking for,” Sen. Claire McCaskill (D-Mo.), a member of the Armed Services Committee, said in a statement.

The Pentagon has been conducting a high-profile campaign to prevent sexual assault and punish offenders amid concerns that it neglected the problem for years.

Despite those efforts, the Defense Department has been embarrassed by several high-profile cases involving senior officers and reports that some commanders have been reluctant to hold accountable those who are accused of sexual offenses.

Congress has already sought to address the problem by imposing a number of changes to the military’s legal system, including ending the statute of limitations on assault and rape cases and making it a crime to retaliate against those who report such crimes.

In March, a majority of the Senate — representing both parties — voted in favor of a more aggressive bill that would have taken away the ability of military commanders to decide which cases should go to court-martial and given those powers to uniformed prosecutors instead. But the bill came up five votes short of the 60 needed to pass a procedural hurdle.

Supporters of that proposal, led by Sen. Kirsten Gillibrand (D-N.Y.), said this week that they would seek another vote by the end of the year.

Both sides are expected to seize on details from the Pentagon’s annual report as ammunition for their arguments.

For instance, Gillibrand noted that the Pentagon’s new data showed that 62 percent of those who reported being sexually assaulted had experienced retaliation or ostracism afterward, whether from superiors or peers in the service. She called that figure “a screaming red flag.” In the report, Defense Department officials said they were also “extremely concerned” by the finding.

The military brass has strongly opposed Gillibrand’s bill, saying that it would undermine commanders’ overall authority and their ability to maintain order and discipline in their units.