"We are almost certainly going to end the year higher than last year," General Peter Chiarelli, the Army's vice chief of staff, told a Pentagon briefing.
"This is horrible, and I do not want to downplay the significance of these numbers in any way."
Another 71 soldiers committed suicide after being taken off active duty in 2009 -- nearly 25 percent more than the end-year total for 2008. Some had returned home only weeks before taking their own lives.
The figures applied only to the U.S. Army. Data from other branches of the armed services was not immediately available.
Chiarelli cautioned against generalizing about the causes of the suicides, or assuming links to combat stress on forces stretched thin by the wars in Iraq and Afghanistan.
He said the causes were still unclear and noted that roughly a third of the soldiers who took their own lives had never been deployed abroad.
The Army recently revealed that about one in five lower rank soldiers suffered mental health problems like depression.
The latest data and this month's shooting spree at a base in Fort Hood, Texas attributed to an Army psychiatrist have raised new questions about the effects of combat stress and the state of the military's mental health system.
The Army has announced it would take a "hard look" at itself to discover how accused shooter Major Nidal Malik Hasan, who is charged with killing 13 people in the November 5 rampage, slipped through the cracks.
As the largest branch of the U.S. armed forces with 1.1 million active duty and reserve soldiers, the Army has done the brunt of the fighting in Iraq and Afghanistan, including years of extended duty and repeated deployments.
President Barack Obama has said he would hold to account those who missed warning signs, which U.S. officials say included Hasan's communications with an anti-American cleric in Yemen sympathetic to al Qaeda.
The military's suicide rate among active-duty soldiers was about 20 per 100,000, nearly double the national U.S. rate of 11.1 suicides per 100,000 people, as reported by the U.S. Centers for Disease Control and Prevention.
Chiarelli said the Army was investigating whether stress related to a future deployment could be a factor in the deaths of soldiers yet to be sent abroad. He said a study being carried out in conjunction with the National Institute of Mental Health could shed some light.
"The reality is there is no simple answer ... I scrub the numbers every way I possible can," Chiarelli said, calling for more substance abuse counselors and mental health professionals to detect early signs of mental illness.