To pay for World War II, Americans bought savings bonds and put extra notches in their belts. President Harry Truman raised taxes and cut nonmilitary spending to pay for the Korean conflict. During Vietnam, the US raised taxes but still watched deficits soar.

But to pay for the ongoing wars in Iraq and Afghanistan, the US has used its credit card, counting on the Chinese and other foreign buyers of its debt to pay the bills.

Now, as President Bush is promising to boost the number of troops in Iraq, there is increased scrutiny over how the US is going to pay for it all.

The US is spending about $10 billion a month on Iraq and Afghanistan. By the end of this year, the total funds appropriated will be nearly $600 billion – approaching the amount spent on the Vietnam or Korean wars, when adjusted for inflation.

However, the actual impact of the war on the economy is different than in the past, largely because the US economy is so much bigger now. During World War II, some analysts calculate that the US spent as much as 30 percent of its gross domestic product (GDP) on the war effort. The Korean War, at its spending peak in 1953, represented 14 percent of GDP; Vietnam was about 9 percent. The current war, however, is less than 1 percent of America's annual $13 trillion GDP.

Payment due: in the future

The US can certainly afford the war, says budget analyst Stan Collender, a managing director of Qorvis Communications in Washington. But the spending is taking resources from other areas, he notes. Because the US is borrowing to finance the war, the cost will be borne by future generations. "And it's still going to be one of the most expensive wars we have ever fought," he says.

Unlike in previous major wars, the United States has cut taxes at the same time it has increased military spending. "It's fair to say all of the money spent on the war has been borrowed," says Richard Kogan, a senior fellow at the Center on Budget and Policy Priorities, a think tank in Washington. "But eventually everything has to be paid for."

Congressional questioning

Congress hopes to hold hearings on the financial implications of the war before the president releases his budget proposal for fiscal year 2008 on Feb. 5. Democrats, now in the majority, plan to ask a wide range of questions, from the future costs of the war to how those costs should be budgeted.

"We won't balance the budget in one year. The best we can expect is five years," says Rep. John Spratt (D) of South Carolina, the new chairman of the House Budget Committee, in a phone interview. "But we need to know: What is the bar we need to reach?"

Estimating the budget deficit has become more difficult in recent years because the White House has funded much of the war through emergency supplemental bills, which are not included in the federal budget. According to a Congressional Research Service report, it is a practice that other administrations have employed since the Korean War. This year, the White House is expected to ask for another $100 billion in supplemental war funds, but Representative Spratt says he would like to get the war back on the budget since it can be argued the war is no longer an emergency.

"Calling it an emergency means the spending does not get the scrutiny," he adds, because then the spending is reviewed by only one committee – House Appropriations. In addition, he says, emergency spending is exempt from caps on discretionary spending. This has prompted the military to include in the bill items that are not directly related to the war. Making the spending a part of the budget would end the practice of some members placing pet projects on a bill that must be passed, he says.

A war-by-war cost comparison

Numbers are fuzzy on how much has been spent so far on the global war on terror. According to the House Appropriations Committee, some $471 billion has been committed so far. Spratt says it's closer to $507 billion. By the end of this year, on a cash basis, the wars in Iraq and Afghanistan will be closing in on the costs of the Vietnam War ($650 billion in today's dollars) and the Korean War ($691 billion).

Some analysts believe the cost of the war is much higher than Congress estimates. In a study last January and updated in October, Harvard Prof. Linda Bilmes and Columbia Prof. Joseph Stiglitz estimated the budgetary and economic cost of the war at $2 trillion.

Ms. Bilmes, in a phone interview, says Congress looks only at its cash outlays, not at the war's future costs. For example, she says, an estimated 42,000 light trucks are in use in Iraq. Although it costs something to run them, the major cost will be replacing them. "That's not factored into the cost of the war," she says.

The same is true of the cost of taking care of injured veterans in the future. "After our study came out, what surprised us is that the VFW, the Vietnam Vets, and others said, 'Thanks for shining the spotlight on this issue, but your numbers are too low,' " Bilmes says. After working with the vets, she concluded that the future costs of caring for the wounded were much higher than she had estimated.

Just the cash costs alone have mushroomed over the past two years, says Steve Kosiak, an analyst at the Center for Strategic and Budgetary Assessments, a think tank in Washington. He estimates that Congress has appropriated nearly $300 billion during that period. "Perhaps some of the additional cost is for repairing the equipment," he says. "But it's fair to say it's partly a mystery why it's up so much."

Polls show people are concerned about the war, says Dennis Jacobe, chief economist at the Gallup Organization in Washington. But, he adds, "they are not concerned about the cost."

This is partly because of the way the war is funded through the supplemental budget process, Mr. Jacobe says. But it's also because the war has not disrupted the economy the same way past wars have. "It's really had no significant impact except for the deficit spending," he says.