WASHINGTON (REUTERS) - Defence Secretary Chuck Hagel ordered top military chiefs on Friday to redouble their effort to address the problem of sexual assault, saying the frequency and perceived tolerance of the crime was eroding the military's ability conduct its mission.

"We're going to fix this problem," Mr Hagel told a news conference a day after he and top military leaders met with President Barack Obama to discuss a series of incidents that have reduced confidence in the services' handling of the crime.

"The president was very constructive. He was very clear.

There wasn't anybody in that room who wasn't disappointed and embarrassed and didn't recognise that we've in many ways failed," Hagel said.

The Pentagon chief issued a memo giving the military heads a week to devise a plan for discussing the sexual assault problem with troops at all levels and ensuring that those who deal with new recruits and sexual assault victims have appropriate training and credentials.

The aim is to ensure that "every member of the armed forces clearly understands that they are accountable for fostering a climate where sexist behaviors, sexual harassment and sexual assault are not tolerated," Mr Hagel said in the memo.

The push for action came a week after the Pentagon issued its annual report on sexual assault in the military, a study that estimated cases of unwanted sexual contact jumped 37 per cent in 2012 to 26,000, versus 19,000 the previous year.

Release of the report came in the midst of a spate of incidents that have caused outrage on Capital Hill over the military's handling of the issue and have led lawmakers to begin working on legislation to address the problem.

The head of the Air Force's sexual assault prevention and response office was arrested the weekend before the report's release and charged with groping a woman while drunk in a parking lot not far from the Pentagon.

In the days following the report, two Army personnel were removed from sexual assault prevention jobs after they came under investigation - one for sexual assault and pandering, and the other after being accused of violating a court protective order obtained by his ex-wife.

"I am concerned that this department may be nearing a stage where the frequency of this crime - and the perception that there is a tolerance of it - could very well undermine our ability to effectively carry out the mission," Mr Hagel said in his memo.

Lawmakers also were outraged over two separate instances in which the senior general in charge of a court martial reviewed a jury's sexual assault verdict and overturned it.

Under the military justice system, the general with ultimate authority over the court martial is required to review the jury's verdict.

The rulings prompted Mr Hagel to ask Congress to amend military law to eliminate the ability of a commander to throw out a jury verdict. Officials say that provision of the law, which dates to the United States (US) revolutionary period, has become outmoded because the system now has a judicial appeals process.

Some lawmakers contend that the decision whether to prosecute a sexual assault case also should be removed from the victim's immediate chain of command and placed in the hands of specially trained military prosecutors.

Senator Kirsten Gillibrand proposed legislation on Thursday to take that step.

"If... a trained military prosecutor can make that judgment about whether a case can go to trial, I think that's going to begin to solve the problem (where)... you have 26,000 assaults a year and only 3,000 reported," she told MSNBC television on Friday.

Air Force Chief of Staff Mark Welsh, who came under fire for citing a "hook-up culture" for part of the problem during congressional testimony, told reporters he was sorry for how his remarks were perceived and hoped to receive input from lawmakers and advocacy groups on how best to address sexual assault.

"There are victims who took what I said as blaming them," he said. "Boy, I am sorry about that because there is nothing that is further from the truth as far as I personally feel."

Mr Welsh said Mr Obama had been clear in his meeting with the chiefs about the need to address the problem. But Mr Welsh said that would require focus and a long-term effort.

"This is not going to be a rapid fix," he said. "It's got to be a constant attention to detail. The task just doesn't end, which is OK. This is about people. It's the most important thing we do."