NEW YORK — When President Barack Obama cited cost as a reason to bring troops home from Afghanistan, he referred to a $1 trillion price tag for America's wars.

Staggering as it is, that figure grossly underestimates the total cost of wars in Iraq, Afghanistan and Pakistan to the U.S. Treasury and ignores more imposing costs yet to come, according to a study released Wednesday.

The final bill will reach at least $3.7 trillion and could be as high as $4.4 trillion, according to the research project "Costs of War" by Brown University's Watson Institute for International Studies.

In the 10 years since U.S. troops went into Afghanistan to root out the al-Qaida leaders behind the Sept. 11, 2001, attacks, spending on the conflicts totaled $2.3 trillion to $2.7 trillion.

Those numbers will continue to soar when considering often overlooked costs such as long-term obligations to wounded veterans and projected war spending from 2012 through 2020.

The estimates do not include at least $1 trillion more in interest payments coming due and many billions more in expenses that cannot be counted, according to the study.

In human terms, 224,000 to 258,000 people have died directly from warfare, including 125,000 civilians in Iraq.

Many more have died indirectly, from the loss of clean drinking water, healthcare, and nutrition. An additional 365,000 have been wounded and 7.8 million people — equal to the combined population of Connecticut and Kentucky — have been displaced.

"Costs of War" brought together more than 20 academics to uncover the expense of war in lives and dollars, a daunting task given the inconsistent recording of lives lost and what the report called opaque and sloppy accounting by the U.S. Congress and the Pentagon.

The report underlines the extent to which war will continue to stretch the U.S. federal budget, which is already on an unsustainable course due to an aging American population and skyrocketing healthcare costs.

It also raises the question of what the United States gained from its multi-trillion-dollar investment.

"I hope that when we look back, whenever this ends, something very good has come out of it," Senator Bob Corker, a Republican from Tennessee, told Reuters in Washington.

In one sense, the report measures the cost of 9/11, the American shorthand for the events of Sept. 11, 2001.

Nineteen hijackers plus other al-Qaida plotters spent an estimated $400,000 to $500,000 on the plane attacks that killed 2,995 people and caused $50 billion to $100 billion in economic damages.

What followed were three wars in which $50 billion amounts to a rounding error. For every person killed on Sept. 11, another 73 have been killed since.

KABUL, Afghanistan — Despite U.S. reports of progress on the battlefield, American troops were killed in the first half of this year at the same pace as in 2010 — an indication that the war’s toll on U.S. forces has not eased as the Obama administration moves to shift the burden to the Afghans.

While the overall international death toll dropped by 14 percent in the first half of the year, the number of Americans who died remained virtually unchanged, 197 this year compared with 195 in the first six months of last year, according to a tally by The Associated Press.

Americans have been involved in some of the fiercest fighting as the U.S. administration sent more than 30,000 extra troops in a bid to pacify areas in the Taliban’s southern heartland and other dangerous areas. U.S. military officials have predicted more tough fighting through the summer as the Taliban try to regain territory they have lost.

President Barack Obama has begun to reverse the surge of American forces, ordering a reduction of 10,000 by the end of the year and another 23,000 by September 2012. But the U.S. military has not announced which troops are being sent home, or whether they will be withdrawn from any of the most violent areas in the south and east.

Rear Adm. Vic Beck, a spokesman for the U.S.-led coalition in Kabul, said he couldn’t comment specifically on the U.S. death count, but noted that the casualties were unchanged despite the surge in forces. He attributed the overall decline in the international toll to coalition progress on the battlefield, including the discovery of a rising number of militant weapons caches. He also said Afghan security forces are increasingly taking the lead, although recent violence has raised concerns about their readiness to secure their own country.

Beck said insurgents were shifting their focus to attacking civilians, pointing to last week’s attack against the Inter-Continental, a luxury hotel in Kabul, that left 20 people dead, including the nine assailants.

“The enemy is taking the fight more to innocent Afghan civilians because we’re taking it to them pretty hard on the battlefield,” he said.

According to the AP tally, 271 international troops, including the Americans, were killed in the first half of the year — down 14 percent from the 316 killed in the first six months of last year.

With the American deaths virtually unchanged, the decline reflects a drop off in deaths of troops from other contributing nations. In the first half of the year, 74 of these troops — from countries like Britain, France and Australia — died compared with 121 in the first six months of last year.