The U.S. risks a fiscal crisis if it doesn't get its large and continually growing federal debt under control, the Congressional Budget Office said today, according to MarketWatch


In its new long-term budget outlook, the nonpartisan CBO said federal debt held by the public now is equivalent to 74 percent of the economy and will rise to 106 percent of the gross domestic product by 2039 if current laws remain unchanged.


In its last long-term budget outlook in September 2013, the CBO said debt held by the public was 73 percent of the GDP and projected debt would be 102 percent of the GDP in 2039.


The stark warning from the CBO comes as deficits have recently been falling. For the current fiscal year, for example, the office is projecting a deficit of $492 billion, which would be 2.8 percent of the gross domestic product.


But the agency expects deficits to rise in coming years as costs related to Social Security, Medicare and interest payments swell.


If federal debt grows faster than the GDP, that path is ultimately "unsustainable" for the economy and risks a crisis where investors would begin to doubt the government's willingness or ability to pay its debt obligations, the CBO said.