WASHINGTON -

Congressional investigators say the federal government is expected to forgive at least $108 billion in student loan debt as part of popular plans that tie repayment to borrowers' earnings.

The Government Accountability Office reviewed income-driven repayment plans the government offers to students struggling to pay back federal student loans. The report says $29 billion more will be discharged due to death or disability.

Those repayment plans have attracted 5.3 million borrowers holding $355 billion in loans.

The GAO report was highly critical of the Education Department's budget estimates for the programs, saying "weaknesses" in its approach could cause costs to be over- or understated by billions of dollars.

The report said the department generally agreed with the GAO's recommendations and was taking steps to improve budget estimates.