With Americans shouldering $1.2 trillion in student loan debt, and about eight million of them in default, Hillary Rodham Clinton on Monday will propose major new spending by the federal government that would help undergraduates pay tuition at public colleges without needing loans.

Mrs. Clinton does not go as far as her Democratic presidential opponents in promising to end tuition debt altogether, since her plan would still require a family contribution that could involve parents taking out loans to cover some tuition.