* Army suicide rate nearly double U.S. national rate
* Many suicides among soldiers who never fought abroad
* U.S. military not near tipping point, top officer says (Adds Mullen comments, background)
WASHINGTON, Nov 17 (Reuters) - Suicides in the U.S. Army will hit a new high this year, a top general said on Tuesday in a disclosure likely to increase concerns about stress on U.S. forces ahead of an expected buildup in Afghanistan.
The findings, released as President Barack Obama inches toward a decision to send up to 40,000 additional troops to Afghanistan, show the number of active-duty suicides so far in 2009 has already matched last year's record of 140 deaths.
"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 top U.S. military officer said on Tuesday deployments were still manageable even though troops would be operating in a "stress window for the next couple of years."
"I certainly don't underestimate, or I would not want to understate the seriousness of the stress issue," Admiral Mike Mullen, chairman of the U.S. military's Joint Chiefs of Staff, told a gathering of business leaders in Washington.
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 Nov. 5 rampage, slipped through the cracks.
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.
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.
In 2008, there were 268 active-duty suicides across the U.S. armed forces, most in the Army.
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. (Editing by Alan Elsner)
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