Washington - More people came forward to report sexual assaults in the military last year, but a significant percentage wouldn't give crucial details needed for an investigation.

    The Pentagon said it received 2,923 reports of sexual assault across the military in the 12 months ending Sept. 30 2008. That's about a 9 percent increase over the totals reported the year before, but only a fraction of the crimes presumably being committed.

    Among the cases reported, only a small number went to military courts, officials acknowledged.

    The Pentagon office that collects the data estimates that only 10 percent to 20 percent of sexual assaults among members of the active duty military are reported - a figure similar to estimates of reported cases in the civilian sphere.

    The military statistics, required by Congress, cover rape and other assaults across the approximately 1.4 million people in uniform.

    Kaye Whitley, director of the Pentagon's Sexual Assault Prevention and Response Office, said most victims are women, most cases involve young people and alcohol is often involved.

    The yearly increase in reports is more likely due to larger numbers of victims being willing to come forward than to an overall increase in sexual violence, Whitley said.

    That increase includes a jump in cases from combat zones in Iraq and Afghanistan, to 165 from 131 the year before.

    Congresswoman Jane Harman, a congressional critic of the military's handling of sexual violence, said the statistics show the problem is still rampant.

    "While the report shows modest improvement, we're far from Mission Accomplished," the California Democrat said in a statement. "Military women are more likely to be raped by a fellow soldier than killed by enemy fire in Iraq."

    The latest figures include 2,280 cases in which a victim provided full accounts and physical evidence when possible, and 643 in which a victim sought care or made a report but refused to provide all the information necessary to pursue an investigation.

    The Defense Department allows those limited reports on the theory that it encourages victims to at least seek care when they might otherwise keep silent.

    Prosecution is slow and large numbers of cases are thrown out or dropped.

    The most recent figures, which include cases left open from previous years, show that only 317 cases were referred for courts-martial, or military trials. Another 247 were referred for nonjudicial punishment.