WASHINGTON—Students accused of sexual assault in the nation’s schools and colleges will gain new due-process protections under proposed rules issued by Education Secretary Betsy DeVos on Friday, though victims’ advocates worry the rules will make it harder to report attacks.

With the new rules, expected for months, the Education Department is rewriting the procedures that colleges use to adjudicate complaints of sexual assault and harassment, and stepping squarely into an emotional debate on campus. Both the accused and alleged...