The number of borrowers defaulting on federal student loans has jumped sharply, the latest indication that rising college tuition costs, low graduation rates and poor job prospects are getting more and more students over their heads in debt.

The national two-year default rate rose to 8.8 percent last year, from 7 percent in fiscal 2008, according to figures released Monday by the Department of Education.

Driving the overall increase was an especially sharp increase among students who borrow from the government to attend for-profit colleges.

Of the approximately 1 million student borrowers at for-profit schools whose first payments came due in the year starting Oct. 1, 2008 — at the peak of the financial crisis — 15 percent were already at least 270 days behind in their payments two years later. That was an increase from 11.6 percent last year.

At public institutions, the default rate increased from 6 percent to 7.2 percent and from 4 percent to 4.6 percent among students at private not-for-profit colleges.

“I think the jump over the last year has been pretty astonishing,” said Debbi Cochrane, program director for the California-based Institute for College Access & Success.

Overall, 3.6 million borrowers entered repayment in fiscal 2009; more than 320,000 had already defaulted last fall, an increase of 80,000 over the previous year.

The federal default rate remains substantially below its peak of more than 20 percent in the early 1990s, before a series of reforms in government lending. But after years of steady declines it has now risen four straight years to its highest rate since 1997, and is nearly double its trough of 4.6 percent in 2005.

Troubling as the new figures are, they understate how many students will eventually default. The rate increased to more than 12 percent when the calculations covered three years.

In 2008 average debt for graduates with loans was $20,200 at public universities, $27,650 at private non-profits and $33,050 at private for-profits.