The attorney general of New Jersey said on Thursday that federal education officials had stopped cooperating on issues involving fraudulent activities at for-profit colleges, and requested that the Education Department renew its investigations into the institutions or hand them over to the state.

Gurbir S. Grewal, who became attorney general in January, expressed frustration with the officials in a letter to Betsy DeVos, the education secretary.

Mr. Grewal said they had ignored requests from New Jersey to work with the state on behalf of students who were defrauded by Corinthian Colleges, a bankrupt for-profit chain. And he raised concerns about the status of investigations by the Education Department into large for-profit institutions like the DeVry Education Group, which paid $100 million in 2016 to settle a lawsuit alleging that it misled prospective students with ads about employment and salaries after graduation.

In an article this week, The New York Times reported that a special investigations team at the Education Department created in the final year of the Obama administration had been unwound under the Trump administration, effectively killing inquiries into DeVry and other schools where top hires of Ms. DeVos previously worked.