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“That would require, for example, roughly a one-half increase in personal income tax revenue. On the other hand, if the change came entirely from spending … that would represent, for example, the near elimination of all government programs except for Social Security, Medicare, Medicaid and national defense,” he said.

The White House said CBO’s scenario doesn’t take into account some of Mr. Obama’s proposals, such as long-term cuts in spending resulting from the new health care law.

Still, Mr. Bixby, the deficit watchdog, said the size of the numbers CBO laid out to the commission shows the tough choices that await Congress. He said the solution will have to be a combination of revenue increases and changes to major programs such as Social Security and Medicare, which are growing at a faster rate than the economy as a whole.

Total public debt includes two pots of money. One is normal government debt in the form of Treasury bills and bonds held by consumers, while the other is intragovernmental holdings, or money one part of the government borrows from another agency. That includes money borrowed from the Social Security trust funds.

Some analysts say the key measure is not the total public debt, but the debt in the hands of consumers. That figure stood at $8.628 trillion on Tuesday.