By Will Dunham

WASHINGTON, April 19 (Reuters) - Nine U.S. senators asked the investigative arm of Congress on Thursday to review possible shortcomings in Pentagon treatment of troops returning with mental health problems from war in Iraq and Afghanistan.

They expressed concern that some military commanders may be minimizing the gravity of post-traumatic stress disorder, or PTSD, and other psychological problems, or suggesting that troops are malingering to avoid further combat deployments.

The senators asked the Government Accountability Office to look into how the Defense Department performs screenings, diagnoses, referrals and treatment of troops coming back with PTSD and other conditions.

"We have also heard of cases in which service members with PTSD are diagnosed as having 'personality disorders' that the Army considers 'pre-existing,' thus depriving otherwise eligible combat veterans of disability benefits and much-needed mental health care," they wrote in a letter to the GAO.

The senators are: Democrats Daniel Akaka of Hawaii, Barbara Boxer of California, Tom Harkin of Iowa, Claire McCaskill of Missouri, Patty Murray of Washington state and Barack Obama of Illinois; Republican Kit Bond of Missouri; and independents Joe Lieberman of Connecticut and Bernie Sanders of Vermont.

Defense Department spokeswoman Cynthia Smith said the Pentagon welcomes a GAO review as requested by the senators.

"No military in the history of the world has done more to prevent, diagnose and treat the mental health concerns of its soldiers more than the modern U.S. military," Smith said by e-mail.

The request to the GAO follows various news reports quoting troops at the Army's Fort Carson in Colorado and elsewhere as saying their pleas for mental health care either went unanswered or they faced abuse and ridicule for seeking help.

President George W. Bush last month apologized to wounded U.S. troops who endured dilapidated conditions and bureaucratic delays at Walter Reed Army Medical Center, the flagship military hospital in Washington. The Army's top civilian leader and other officials were ousted over the Walter Reed revelations.

But there also have been questions about military mental health care.

The GAO reported last year that just 22 percent of U.S. troops returning from Iraq and Afghanistan who showed signs of PTSD were being referred by Pentagon health care providers for mental health evaluation.

The American Psychological Association said in February the military's understaffed and poorly coordinated mental health care system was not meeting the needs of troops and their families.

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