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Under either scenario, the CBO said discretionary spending — the money that goes to basic functions such as law enforcement, education and the like — is slated to drop to a lower percentage of gross domestic product than at any other time in the past five decades. But entitlement programs, which are on autopilot, will more than make up for that, increasing from 13.3 percent of the economy in 2013 to 14.3 percent in 2022.

Also, interest payments on the debt will absorb an ever-larger part of the budget.

For the past three years, the government has collected taxes at a rate of about 15 percent of the economy while spending at a rate of about 24 percent of the economy. That gap explains the staggering deficits.

For 2012, those numbers will improve to 16 percent of GDP in taxes, while spending will account for 23 percent of GDP.

The post-World War II average has been about 18 percent in taxes and 20 percent in spending.

Mr. Obama will submit his 2013 budget in February, but he signaled in his State of the Union address that much of it will depend on tax increases for those with the highest incomes. He has said he wants to impose a “Buffett Rule” — named after billionaire Warren Buffett — that would set an alternative minimum tax of 30 percent on incomes for the wealthiest Americans.

Congress is still struggling to deal with the original alternative minimum tax, created in the late 1960s to make sure wealthy Americans paid their share.

At the time, lawmakers failed to index the income level at which the tax hit, meaning that the higher tax affected more Americans every year. For the past two decades, Congress has had to enact patches that prevent an ever-wider swath of taxpayers from being affected.

The CBO report says continued patches to the alternative minimum tax is one reason why the budget outlook is so grim. Over the next 10 years, Congress will forgo more than $800 billion in revenue if it adjusts that tax rate — about equal to the size of the entire stimulus package Mr. Obama and Democrats enacted in 2009.

Congress and the president did make some strides last year toward a better budget.

They cut discretionary spending, putting it on a path that the CBO said would lead to levels, measured as a percentage of the economy, that haven’t been seen in five decades. They also implemented a structure to cut still more.

The CBO also warned that progress would be undermined if lawmakers undo automatic cuts called resulting from a supercommittee’s failure last year to suggest more than $1.2 trillion in other savings.