More than a quarter of higher-ranking enlisted soldiers showed signs of mental health problems after being sent to war zones for the third or fourth time, a sharp increase over those on their first or second deployments, according to a military study issued Thursday.

The findings of a new Army report on the behavioral health of soldiers in Iraq are the first to quantify the stress of repeated deployments on combat soldiers. The data are likely to increase calls by senior Army leaders to cut the length of combat tours and increase the time soldiers have between deployments.

Although the Army has been measuring the mental health of troops in Iraq since the beginning of the war, the study is the first to draw clear conclusions about troops on their third or fourth tours, the authors said.

The report showed that 27.2% of noncommissioned officers -- the sergeants responsible for leading troops in combat -- reported mental health problems during their third or fourth tours. That was up from 18.5% of those on their second tour and 11.9% of those on their first tour. Mental health problems include signs of depression, anxiety and stress disorders.

The report showed a sharp decline in morale for those on their third and fourth tours -- with 15.6% saying they had "very high morale," down from 27.1% for NCOs on their first deployment -- as well as a significant increase in problems doing their jobs.