A Connecticut veteran of the Iraq War has sued the Army, saying he was denied full education and retirement benefits after he was diagnosed with adjustment disorder while actually suffering from post-traumatic stress disorder.

William Cowles, a 57-year-old East Haven resident, filed the lawsuit Thursday in U.S. District Court in Connecticut challenging the denial of his application for medical retirement. The lawsuit seeks to change his discharge so he can receive full benefits.

Because Cowles was discharged for adjustment disorder rather than medically retired for PTSD, he is eligible for only half the education benefits he would have received and lost about $18,000 in retirement benefits, according to the lawsuit.

‘‘The Army rushed me out the door without proper medical attention,’’ Cowles said in a statement. ‘‘I hope that my case can bring attention to this issue and help other veterans in my position get the benefits they deserve.’’

The Army declined to comment on the case, saying it doesn’t discuss pending litigation. But a spokesman said the Army never discharges soldiers to avoid providing the needed medical care and benefits.

‘‘Standards of discipline and accountability apply to every soldier, whether assigned to a unit or to a warrior-care environment,’’ said Army spokesman Troy A. Rolan Sr. “We have a process that is fair, objective and methodical to ensure that good order and discipline is maintained within the ranks. ”

Cowles joined the Army National Guard in 1974 as a combat engineer. In 2003, he deployed to Iraq, where he witnessed the death of men from his unit and the brutal killing of a civilian truck driver, according to the lawsuit.

Cowles suffered a breakdown and was medically evacuated. After two brief evaluations, the Army determined that he had adjustment disorder — meaning he was temporarily struggling to cope with a stressful life event — and immediately discharged him, but two months later, the U.S. Department of Veterans Affairs diagnosed him with service-connected PTSD, which is a much more severe, long-term disability induced by experiencing trauma, his representatives say.

The Army Board for Correction of Military Records denied Cowles’s request last year to correct his discharge to medical retirement, according to the lawsuit.

‘‘The ABMCR has denied every single application from veterans who received discharges for adjustment disorder and requested corrections to military retirement for PTSD in the past decade,’’ said Sopen Shah, a law student intern of the Veterans Legal Services Clinic at Yale Law School, which represents Cowles. ‘‘This discrimination against disabled veterans is intolerable.’’

The Government Accountability Office, members of Congress, and Vietnam Veterans of America have criticized the Army for discharging service members based on erroneous diagnoses of adjustment disorder and personality disorder who actually have PTSD, according to Cowles representatives.

‘‘We commend Mr. Cowles for leading the charge to correct these mistakes, which deny veterans improperly separated for adjustment disorder the medical care, recognition, and benefits they have earned,’’ said John Rowan, national president of Vietnam Veterans of America.