Graduate students, not undergrads, are increasingly driving the country's student debt crisis, and the federal government will likely end up footing much of the bill, according to a study released today by the New America Foundation.

Most studies have historically lumped together undergraduate and graduate debt, leading politicians and media reports to focus primarily on the high price of bachelor's and associate degrees. But when graduate debt is isolated, as it was in this study, a striking picture emerges.

Around 40% of the more than $1 trillion in outstanding student loans went to financing graduate and professional degrees, the study found. Combined debt levels of the average graduate borrower, according to the study, have surged by $17,000 — from $40,000 in 2004 to more than $57,000 in 2012, adjusted for inflation. For the average undergraduate borrower, that increase was just $7,580, according to the separate New America Foundation report.

While the higher debt level is more manageable for medical school students, for instance, it could be crippling for Master of Arts students, among whom the median debt is $58,000.

Some of the study's more eye-popping statistics pertained to law school students, whose job prospects are famously declining. The level of indebtedness for this group rose by more than $50,000 from 2008 to 2012, with the typical law student now owing $140,000, the study found — a jump that's unprecedented in any other field, including medicine.

"Most of these degrees are not intuitively worth it. They're not gateways to the middle class," says Jason Delisle, the study's author. "Is a Master of Arts degree really worth $20,000 more than it was in 2004?"