In concrete terms, an additional $500 billion a year in interest expense would total more than the combined federal budgets this year for education, energy, homeland security and the wars in Iraq and Afghanistan.

The potential for rapidly escalating interest payouts is just one of the wrenching challenges facing the United States after decades of living beyond its means.

The surge in borrowing over the last year or two is widely judged to have been a necessary response to the financial crisis and the deep recession, and there is still a raging debate over how aggressively to bring down deficits over the next few years. But there is little doubt that the United States’ long-term budget crisis is becoming too big to postpone.

Americans now have to climb out of two deep holes: as debt-loaded consumers, whose personal wealth sank along with housing and stock prices; and as taxpayers, whose government debt has almost doubled in the last two years alone, just as costs tied to benefits for retiring baby boomers are set to explode.

The competing demands could deepen political battles over the size and role of the government, the trade-offs between taxes and spending, the choices between helping older generations versus younger ones, and the bottom-line questions about who should ultimately shoulder the burden.

“The government is on teaser rates,” said Robert Bixby, executive director of the Concord Coalition, a nonpartisan group that advocates lower deficits. “We’re taking out a huge mortgage right now, but we won’t feel the pain until later.”

So far, the demand for Treasury securities from investors and other governments around the world has remained strong enough to hold down the interest rates that the United States must offer to sell them. Indeed, the government paid less interest on its debt this year than in 2008, even though it added almost $2 trillion in debt.

The government’s average interest rate on new borrowing last year fell below 1 percent. For short-term i.o.u.’s like one-month Treasury bills, its average rate was only sixteen-hundredths of a percent.