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.

But her proposals, which would cost $350 billion over 10 years and include new refinancing options for those already struggling with debt, are an aggressive response to what many Americans — Democrats and Republicans alike — see as a worsening crisis forcing young adults to move back home with their parents and struggle to get out from under repayment bills.