WASHINGTON, Jan 26 (Reuters) - The cost to U.S. taxpayers of the wars in Iraq and Afghanistan since 2001 has topped $1 trillion, and President Barack Obama is expected to request another $33 billion to fund more U.S. troops this year.

About two-thirds of the money has been spent on the conflict in Iraq since 2003. This year is the first in which more funds are being spent in Afghanistan than Iraq, as the pace of U.S. military operations slows in Iraq and quickens in Afghanistan.

HOW MUCH HAS BEEN SPENT ALREADY?

Congress has approved $1.075 trillion dollars for military operations in Iraq and Afghanistan and “war-related activities” since 2001, according to the nonpartisan Congressional Budget Office. It included the costs in its budget outlook Tuesday.

The war expense topped $1 trillion in December 2009, when U.S. lawmakers approved the fiscal 2010 defense spending bill that included about $130 billion to be spent on the two conflicts through Sept. 30, 2010.

The $1.075 trillion tally includes $51 billion for diplomatic activities and aid to Iraq, Afghanistan and various other countries that are assisting the United States in fighting terrorism, CBO said.

HOW MUCH WENT FOR IRAQ AND HOW MUCH FOR AFGHANISTAN?

The lion’s share of the spending -- $708 billion -- has been allocated to the war in Iraq since the U.S.-led invasion there in 2003, according to CBO. Former President George Bush launched the Iraq war in a search for weapons of mass destruction, which never were found.

CBO said $345 billion has gone to Afghanistan, where the United States invaded to fight al Qaeda and topple the Taliban after the Sept. 11 attacks in 2001. About $22 billion went for war-related activities in other countries, it said.

The current fiscal year, which ends Sept. 30, is the first year that more money has been allocated to Afghanistan ($72.3 billion) than Iraq ($64.5 billion), according to the National Priorities Project, a nonpartisan budget research group that has a running tally of the wars’ costs on its Website.

The group included some U.S. homeland security spending in those 2010 cost tallies. It examines congressional appropriations, while CBO has access to additional sources, including Pentagon spending reports.

HOW MUCH MORE WILL THESE OPERATIONS COST?

Obama announced in December he was adding 30,000 more U.S. troops to the Afghan war effort to join the 68,000 already fighting a resurgent Taliban. Defense officials say he will shortly ask Congress for $33 billion to pay for the cost of the troop surge in fiscal 2010.

Future expenses are a question mark, partly because troop levels are uncertain. Obama says he wants to start withdrawing forces from Afghanistan in mid-2011, but that will depend, in part, on conditions on the ground. No departure deadline has been set.

Estimates of the cost per troop per year in Afghanistan vary from $500,000 to $1 million depending on whether expenditures on troop housing and equipment are included along with pay, food and fuel. Medical costs for the injured and veterans’ compensation balloon as time goes on.

In Iraq, the U.S. force is supposed to fall to 50,000 by the end of August, from some 115,000 last month. The 50,000 can remain until the end of 2011, under an agreement with Baghdad.

A year ago CBO projected that additional costs for the Iraq and Afghanistan conflicts could be $867 billion over the next decade, if combined troop levels fall to 75,000 by about 2013.

WHY ARE SOME COSTS GROWING?

One expanding line item is the money being spent on on Iraq’s and Afghanistan’s troops. CBO said the United States has spent $49 billion to date on training and equipping military and police units in the two countries.

“That number may get larger in the future because it is central to our exit strategy, which is preparing Afghanistan to take over security so we can leave,” said Christopher Hellman, research director for the National Priorities Project.

Obama is preparing to ask Congress next week for $11.6 billion more to train the Afghan security forces in 2011, draft Pentagon budget documents say.

WHAT ARE THE POLITICAL RISKS?

Obama’s Democratic Party has the majority in Congress but is divided over the wisdom of continuing the Afghan war. This means he needs Republicans to get congressional approval of the next tranche of funds sometime this spring.

He is expected to get that approval, in part because many lawmakers who don’t approve of sending more combat troops are loath to cut off funds to soldiers in the field.

But with Americans tiring of war and getting more concerned about U.S. indebtedness, political pressures are expected to grow for winding down U.S. military operations and their costs in Iraq and Afghanistan.