Reports of sexual assaults in the military increased by nearly 40 percent last year, the Pentagon announced Thursday, saying the increase was at least partly due to a new program that encourages victims to come forward.

According to a report released Thursday, there were 2,374 allegations of sexual assaults reported during 2005, compared to 1,700 in 2004. Of last year's reports, 435 were initially filed under a new program that allows victims to report the incident and receive health care or counseling services but does not notify law enforcement or commanders.

The restricted, confidential reporting program also allows the victims to consider pursuing an investigation later, and that was done in 108 of the 435 cases during 2005. Until that new policy went into effect last June, an investigation was automatically triggered by a sexual assault report.

"This is the most underreported crime in our society," said Roger Kaplan, a Pentagon spokesman. "The key, at least in the military, is to make it less. We want victims to have treatment. And the more who come forward, the better chance we have of taking action and getting the offenders off the street."

Kaplan said it is impossible to tell whether the increase in reports during 2005 signals any actual increase in sexual assaults. But he said he believes it shows that the military's extensive program in recent years to better train troops and to encourage reporting has been successful.

According to the Defense Department, the military services have set up sexual assault program offices at all major installations and trained more than 1,000 response coordinators and victim advocates. The Army, for example, also has a sexual assault coordinator deployed with each brigade and a victim's advocate with every battalion, said Kaplan.

Of the cases that were fully investigated in 2005, nearly 1,400 — or 68 percent — were completed by the end of the year. No action was taken against more than 800 alleged offenders because the incident was unfounded, there was a lack of evidence or the person was not identified.

Among the remaining cases that were finalized, 79 people received courts-martial, 91 were given nonjudicial punishments and 104 were discharged or otherwise reprimanded.

The military has come under fire for repeated problems with sexual abuse at the service academies, in units stationed abroad in Iraq, Kuwait, Afghanistan or Bahrain, and at military installations. Detainee abuse allegations have also included sexual assaults.

The Air Force Academy in Colorado is still struggling to recover from complaints that dozens of female cadets were assaulted and then punished when they reported it. And a recent survey by the Veterans Affairs Department showed that six in 10 women who served in the National Guard and Reserves say they were sexually harassed or assaulted.