Almost one in six Vietnam veterans suffers from post-traumatic stress syndrome and almost half have had a psychiatric disorder at some point in their lives, a study showed Wednesday.

The four-year study, conducted for the Veterans Administration, found about 479,000, or 15.2 percent, of the 3.1 million male veterans who served in Vietnam now have post-traumatic stress syndrome or PTSD. About 8.5 percent of the 7,000 female Vietnam veterans have PTSD.Post-traumatic stress syndrome is a mental disorder sparked by exposure to violent incidents, such as combat, which then return as recurrent images that disrupt normal life. Symptoms may include nightmares, insomnia, drug or alcohol abuse, depression and withdrawal from social activities.

In its study, Research Triangle Institute of North Carolina found black and Hispanic veterans were more likely than whites to be stricken by PTSD. About 28 percent of the 168,000 male Hispanic veterans and 20 percent of the 352,000 black veterans suffer from the syndrome, compared to about 14 percent of veterans who are white or from other racial groups.

The nationwide survey also found about half of veterans serving in the Vietnam war theater had at least one psychiatric problem at some point in their lives - with alcohol abuse accounting for the greatest proportion. Researchers said that rate is not substantially higher than among soldiers who were stationed elsewhere, but is "significantly higher" than among civilians.

In addition, the study, ordered by Congress in 1983, showed Vietnam veterans exposed to "high levels of war stress" had higher rates of divorce and family problems than soldiers who saw little or no combat.

VA Administrator Thomas Turnage said the agency will use the study results to determine how well its programs serve Vietnam veterans. The study found only about 20 percent of veterans suffering from PTSD have sought treatment from the VA.

Barry Kasinitz, a spokesman for the Vietnam Veterans of America, called the new survey - the first to look at readjustment problems among Vietnam era veterans in all branches of the military - a "very significant study."