WASHINGTON (Reuters) - The cost to U.S. taxpayers of 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 troops this year.

Over 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 $1.05 trillion dollars for the wars in Iraq and Afghanistan, according to the National Priorities Project, a nonpartisan budget research group that has a continuously running war cost counter on its website.

The tally topped $1 trillion last month, when U.S. lawmakers approved the fiscal 2010 defense spending bill that included $128 billion to be spent on the two conflicts through September 30. The trillion-dollar total includes war-related costs incurred by the State Department, like embassy security.

HOW MUCH WENT FOR IRAQ AND HOW MUCH FOR AFGHANISTAN?

The lion’s share of the spending -- $747.3 billion -- has been allocated to the war in Iraq since the U.S.-led invasion there in 2003.

The other $299 billion has been for Afghanistan, where the United States invaded to fight al Qaeda and topple the Taliban after the September 11 attacks in 2001.

War funding for fiscal 2010, which ends September 30, included $72.3 billion for Afghanistan and $64.5 billion for Iraq, making this the first year that Afghanistan was more expensive, the National Priorities Project said.

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 68,000 already there fighting a resurgent Taliban. Defense officials say he will shortly ask Congress for $33 billion to pay for the surge, when he sends lawmakers his budget request.

That would take care of 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 this will depend in part on conditions on the ground. No deadline for leaving 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 the Congressional Budget Office 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.

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.

“I think that in general the American people, while obviously this is very difficult financially for us, will continue to support the troops that are there and the Congress will reflect that,” Senate Armed Services Committee Chairman Carl Levin said this week.

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.