At least 128 soldiers killed themselves in 2008, said two officials who spoke on condition of anonymity because the data has not been formally released.
The final count likely will be considerably higher because more than a dozen other suspicious deaths are still being investigated and could also turn out to be self-inflicted.
The new figure of more than 128 compares to 115 in 2007 and 102 in 2006 - and is the highest since record keeping began in 1980.
It also calculates to a rate of 20.2 per 100,000 soldiers - which is higher than the adjusted civilian rate for the first time since the Vietnam War, officials said.
The Army plans to announce the figures at a news conference later Thursday.
Officials have said repeatedly that troops are under tremendous and unprecedented stress because of repeated and long tours of duty due to the simultaneous wars in Iraq and Afghanistan.
Yearly increases in suicides have been recorded since 2004, when there were 64 - only about half the number now. And they've occurred despite increased training, prevention programs, increased psychiatric staff and other Army efforts to stem the rise.
Officials are expected to announce additional attempts to help soldiers at the news conference.
When studying individual cases, officials said they found that the most common factors for suicides were soldiers suffering problems with their personal relationships, legal or financial issues and problems on the job.
The previous number of suicides, combined, among the Army's active-duty soldiers and National Guard and Reserve troops also was the highest on record - 18.8 per 100,000. But the new pace of 20.2 suicides per 100,000 soldiers is startling because it for the first time surpasses the civilian number, when adjusted to reflect the Army's younger and male-heavy demographics.
The Centers for Disease Control and Prevention said the suicide rate for U.S. society overall was about 11 per 100,000 in 2004, the latest year for which the agency has figures. But the Army says the civilian rate is more like 19.5 per 100,000 when adjusted.
The new rate of 20.2 - which also will be higher if more suicides are confirmed - compares to 18.8 per 100,000 in 2007, 17.5 in 2006 and 9.8 in 2002 - the first full year after the start of the war in Afghanistan
The new Army report follows one earlier this month showing that the Marine Corps recorded more suicides last year than any year since the U.S.-led invasion of Iraq in March 2003.
That report said 41 Marines were possible or confirmed suicides in 2008, or 16.8 per 100,000 troops. The Marine rate remained unchanged because the Corps is increasing in size, officials said.
Marines and Army units have borne most of duty in the two wars, which have required more use of ground forces to fight the insurgencies.
But the numbers kept by the service branches do not show the whole picture of war-related suicides because they do not include deaths after people have left the military. The Department of Veterans Affairs tracks those numbers and says there were 144 suicides among the nearly 500,000 service members who left the military from 2002-2005 after fighting in at least one of the two ongoing wars.
The true incidence of suicide among veterans is not known, according to a report last year by the Congressional Research Service. Based on numbers from the Centers for Disease Control and Prevention, the VA estimates that 18 veterans a day - or 6,500 a year - take their own lives, but that number includes veteranss from all previous wars.