Although there seems to be complacency in the budget discussions in Washington, the country "still faces a dangerous fiscal deficit," says Martin Feldstein, a professor of economics at Harvard and chairman of Reagan's Council of Economic Advisors.

The Congressional Budget Office (CBO) predicts the budget deficit will drop from 7 percent in 2012 to 4 percent of gross domestic product (GDP) in 2013 due to the sequester-mandated spending cuts and higher tax rates. The CBO also predicts the deficit will fall to 2.1 percent of GDP in 2015, then rise to just 3.5 percent in 2023.

Not too likely, Feldstein writes in an article for Project Syndicate. "Even the CBO does not believe that they represent what will occur."

Video: Economist Predicts 'Unthinkable' for 2013

That's because the forecast is a baseline scenario that assumes all deficit-reducing features now law will remain in place. For instance, it assumes Medicare payments to physicians will be cut sharply in the future, even though Congress postpones cutting those payments every year.

The CBO's alternative scenario, which lacks such unlikely features, indicates that the deficit will increase to 4.7 percent of GDP in 10 years, with the debt-to-GDP level at 83 percent and rising.

"Officials and others who favor stimulating growth through increased government spending ignore the CBO's more realistic alternative scenario," Feldstein writes.

Those advocating more government spending to stimulate growth say the deficit is not an immediate concern because government-borrowing rates are now very low. But that's just because "the Federal Reserve is now buying more long-term securities than the government is issuing to finance the budget deficit," Feldstein counters.

The CBO warns that an aging population and rising medical costs will lead to the fiscal deficit rising to 17 percent of GDP in 2037.

Controlling the debt requires slowing the growth of healthcare programs and government pensions and increasing tax revenues.

"Tax revenue can be raised without increasing marginal tax rates by limiting the tax subsidies that are built into the current tax code," he writes. "Those subsidies are a hidden form of government spending on everything from home mortgages and health insurance to the purchase of hybrid cars and residential solar panels."

Economist Paul Krugman takes the opposing view. The budget doesn't have to be balanced to put the country on a fiscally sustainable, Krugman writes in his New York Times column. It just needs to grow slower than the economy.

The debt doubled in the 30 years after World War II, but fell as a percentage of GDP by three-quarters in the same period, he noted.

"So we do not, repeat do not, face any kind of deficit crisis either now or for years to come."

Video: Economist Predicts 'Unthinkable' for 2013