President Obama summoned the Pentagon’s leadership to the White House on Thursday for a crisis meeting about sexual assault in the armed forces, but the commander in chief said that “there’s no silver bullet to solving this problem.”

In a brief appearance after the session, Obama said sex crimes in the military are “dangerous to our national security” and “not a sideshow.” He said military officials had told him “that they’re ashamed by some of what’s happened,” and he pledged to work with Congress on legislation to address the issue.

Despite years of intensive efforts to confront the problem, military commanders earlier admitted their collective failure in frank confessionals and seemed at a loss for answers.

“The Army is failing in its efforts to combat sexual assault and sexual harassment,” Gen. Ray Odierno, the Army’s chief of staff, said in a blog post addressed to his 540,000 soldiers. “It is time we take on the fight as our primary mission.”

Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, said the military was mired in a “crisis” and suggested that fatigue from more than a decade of war might be a factor. “We’re losing the confidence of the women who serve that we can solve this problem,” he told reporters as he flew back to Washington from Brussels.

In another sign of how the Pentagon is struggling to cope, Charles A. Blanchard, the chief legal and ethics officer for the Air Force, issued an unusual public plea, via Twitter, for “more ideas on ending sexual assault in the military.” In a blog post, he added: “What issues are those of us in the Beltway ignoring?”

Dempsey and Defense Secretary Chuck Hagel canceled a scheduled news conference at the Pentagon to meet instead at the White House with Obama and leaders from the Army, Navy, Air Force and Marine Corps.

Hagel issued an emergency order Tuesday night to retrain and rescreen all 9,000 sexual-assault-prevention officers in the military after the Army disclosed that it was investigating one of them, based at Fort Hood, Tex., on suspicion of “abusive sexual contact” and forcing a subordinate into prostitution.

Ten days earlier, the Air Force’s top sexual-assault-prevention officer was arrested on charges that he drunkenly groped a woman.

The Pentagon has been slow to provide details of how Hagel’s order will be carried out. About 3,000 sexual-assault-prevention officers had been freshly trained and certified since October. Defense officials said those officers might have to go through it all again, although it was unclear if the process would be different.

The Army said Thursday that its investigation at Fort Hood was continuing and that no charges had been filed. Authorities have not identified the suspect except to describe him as a sergeant first class at III Corps.

According to soldiers at Fort Hood who know the suspect, however, Army officials in recent days have scoured Web sites and office bulletin boards to remove any photographs and documents containing the sergeant’s name or image.

The Army did the same thing in March 2012 before it publicly identified Staff Sgt. Robert Bales as the suspect in the fatal shootings of 16 Afghan civilians, the worst atrocity of the war.

Despite the lurid allegations at Fort Hood, one female soldier in the same battalion as the suspect said she wasn’t surprised by the news, citing a pattern of intimidation against sex-crime victims.

The 25-year-old soldier, who spoke on condition of anonymity because she feared retaliation, said she was sexually assaulted at Fort Hood in December 2011. When she reported the attack, her commander tried to blame her for provoking the incident, she said, and a sexual-assault-prevention coordinator “kind of swept it under the rug and told me, ‘You just took it the wrong way.’ ”

The assault was only properly investigated, the soldier said, after she made an appeal to Eric Shinseki, the retired general who is secretary of veterans affairs, when he visited Fort Hood. Her assailant was convicted and sentenced to a year in prison.

“I’m one of the few lucky ones who got justice,” she said.

Meanwhile, on Capitol Hill, a split was emerging among lawmakers who have pledged legislative action to combat sex crimes in the military.

One group, led by Sen. Kirsten Gillibrand (D-N.Y.), is pushing to overhaul the military justice system so that prosecutors, instead of commanders without legal training, have the authority to decide whether to investigate serious crimes and bring defendants to trial.

Other lawmakers, however, said it was more important to hold commanders accountable for how they respond than to change the legal system.

“It’s far too soon to take a hatchet to the judicial system,” said Rep. Michael R. Turner (R-Ohio), a member of the House Armed Services Committee. “The problem is a cultural issue.”