Democratic attorneys general from 18 states and the District of Columbia filed a lawsuit on Thursday against the Education Department and its secretary, Betsy DeVos, challenging the department’s move last month to freeze new rules for erasing the federal loan debt of student borrowers who were cheated by colleges that acted fraudulently.

The rules, known as borrower defense, were finalized in October by the Obama administration after years of negotiation and review, and they had been scheduled to take effect on July 1. But after President Trump took office, Ms. DeVos paused the planned changes, citing a federal lawsuit filed in May by an association of for-profit colleges in California that sought to block the rules.

Ms. DeVos also criticized the rules, calling them “a muddled process that’s unfair to students and schools,” and she said she would establish a new rule-making committee to reconsider the matter from scratch.

In their lawsuit, filed in Federal District Court in Washington, the states called the agency’s rationale for the delay — the California lawsuit — a “mere pretext” for repealing and replacing rules that had already been finalized. The states are seeking to have the rules restored.