Mayor Eric Adams announced painful budget cuts to New York City services on Thursday that would freeze police hiring and close libraries on Sunday and warned that more cuts would be necessary without additional federal funding to manage the migrant crisis.

The budget cuts would bring the number of Police Department officers below 30,000, slash the Education Department budget by $1 billion over two years and delay the rollout of composting in the Bronx and Staten Island — one of the mayor’s signature initiatives to address rats and climate change. The cuts would also weaken two popular programs: summer school and universal prekindergarten.

Mr. Adams said in a statement that he had to make cuts across city agencies in response to the rising costs of the migrant crisis, slowing tax revenues and the ending of federal pandemic aid.