Under the drawdown already planned, the departure of five combat brigades from Iraq by July should allow the Army to announce that tours will be shortened to 12 months from 15 by the end of summer.

Image Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, warned of the toll the Iraq war could take on the military. Credit... Mark Wilson/Getty Images

Even so, senior officers warn that time at home must be increased from the current 12 months between combat tours. Otherwise, they say, the ground forces risk an unacceptable level of retirements of sergeants  the key leaders of the small-unit operations  and of experienced captains, who represent the future of the Army’s officer corps.

The mental health study conducted by the Army was carried out in Iraq last October and November, and does not represent a purely scientific sampling of deployed troops, because that is difficult to accomplish in a combat environment, the authors of the study have said. Instead, the study was based on 2,295 anonymous surveys and additional interviews from members of frontline units in combat brigades, and not from those assigned primarily to safer operating bases. Since the study was distributed last month, it has become a central topic of high-level internal discussions within the Army, and its findings have been accepted by Army leaders, senior Pentagon and military officials say.

The survey found that the proportion of soldiers serving in Iraq who had encountered mental health problems was about the same as found in previous studies  about 18 percent of deployed soldiers. But in analyzing the effect of the war on those with previous duty in Iraq, the study found that “soldiers on multiple deployments report low morale, more mental health problems and more stress-related work problems.”

By the time they are on their third or fourth deployments, soldiers “are at particular risk of reporting mental health problems,” the study found.

The range of symptoms reported by soldiers varies widely, from sleeplessness and anxiety to more severe depression and stress. To assist soldiers facing problems, the Army has begun to hire more civilian mental health professionals while directing Army counselors to spend more time with frontline units.

Senior officers at the Pentagon have tried to avoid shrill warnings about the health of the force, cognizant that such comments might embolden potential adversaries, and they continue to hope that troop levels in Iraq can be reduced next year. Still, none deny the level of stress on the force from current deployments.