Lori Montgomery / The Washington Post

WASHINGTON — As President Barack Obama and congressional Republicans argue over how to rewrite the U.S. tax code, the debate has revolved around “loopholes” for corporate jets and ending “carve-outs” for well-heeled special interests. But if the goal is debt reduction, that’s not where the money is.

Broad tax breaks granted to millions of families at all income levels dwarf the corporate giveaways. Over the past two years, largely because of these popular benefits in the federal income tax code, the government has reached a rare milestone in tax collection: It has given away as much as it takes in.

The number of tax breaks has nearly doubled since the last major tax overhaul 25 years ago, with lawmakers adding new benefits for children, college tuition, retirement savings and investment. At the same time, some long-standing breaks have exploded in value, such as the deduction for mortgage interest and the tax-free treatment of health-insurance premiums paid by employers.

All told, federal taxpayers last year received $1.08 trillion in credits, deductions and other perks while paying $1.09 trillion in income taxes, according to government estimates.

Only about 8 percent of those benefits went to corporations. (The write-off for corporate jets equals about .03 percent of the total.) The bulk went to private households, primarily upper middle-class families that Obama has vowed to protect from new taxes.

“The big money is in the middle-class subsidies,” said Syracuse University economist Leonard Burman, former director of the nonpartisan Tax Policy Center. “You’re not going to balance the budget by eliminating ethanol credits. You have to go after things that really matter to a lot of people.”

These tax breaks weave an invisible web of government benefits that now costs nearly as much as the Pentagon and all other federal agencies combined. But “tax expenditures,” as they are known in Washington, get no routine oversight. Congress and the Treasury Department both track them but use different rules to count them and estimate their value. The congressional Joint Committee on Taxation lists more than 300 breaks, while Treasury tallies 172.

No one regularly assesses whether tax expenditures accomplish the goals they were created to serve. Yet, with the rise of an ideology within the Republican Party that shuns big government and vilifies taxes, they have become virtually untouchable.

For those reasons, the tax code is a popular venue for both parties to pursue costly policy goals.

Edward Kleinbard, a University of Southern California law professor who served until recently as chief of staff to the Joint Committee on Taxation, says tax breaks are now the dominant instrument for creating new spending programs. Policymakers can give taxpayers a government benefit and get credit for lowering their tax bills. This is a combination lawmakers find “irresistible,” Kleinbard said, because they can portray themselves as tax cutters rather than big spenders.

Every president since Ronald Reagan has learned that lesson. In 1997, after a Republican Congress refused to increase spending for federal student loans, President Bill Clinton turned to the tax code to create a slew of higher-education credits. Initially worth around $10 billion a year to the nation’s college students, those benefits have been expanded to more than $20 billion annually.

Similarly, when President George W. Bush wanted to help victims of the Sept. 11, 2001, attacks, he turned to the tax code. He backed the Victims of Terrorism Tax Relief Act, which wiped out two years of tax liability for survivors and created a continuing exemption for annuities paid to families of public-safety officers killed in the line of duty. Estimated 10-year price tag: $360 million.

In 2009, when Obama wanted to boost the flagging economy, he offered a huge new tax break as the centerpiece of his stimulus package. The Making Work Pay credit put about $60 billion a year in people’s pockets in 2009 and 2010, including $18 billion in “refundable” payments to low-income families whose tax bills were so small that the government had to write them checks to make sure they received the full value.

This week, Obama is expected to offer an outline for revising the tax code to weed out special tax breaks. At the same time, he is pressing Congress to create several more. His $447 billion jobs package includes a $4,000 credit for hiring people who have been out of work more than six months and a $5,000 credit for hiring returning war veterans.

Administration officials say targeted tax cuts are an easy way to quickly put money in people’s pockets. But they also acknowledged the political reality that lawmakers are more inclined to support a plan that cuts taxes than one that increases spending.

Once a tax break is ensconced in the code, it is hard to dislodge. Beneficiaries become fierce defenders, as do anti-tax conservatives, who view the end of a tax break as an impermissible hike in overall tax collections. About 95 percent of Republicans in Congress, and a few Democrats, have signed a pledge circulated by GOP strategist Grover Norquist vowing to “oppose any net reduction or elimination of deductions and credits, unless matched dollar for dollar by further reducing tax rates.”