Mayor Bill de Blasio’s press secretary will leave her post next month, the latest sign that the administration is continuing its long struggle to control and disseminate its own message.

The press secretary, Karen Hinton, sent a letter of resignation last month, a person familiar with the matter said; Ms. Hinton is expected to depart after the budget is made final, most likely in June, roughly a year after she was hired.

In his two and a half years as mayor, Mr. de Blasio, a Democrat, has often lamented that his liberal policies have not been clearly conveyed to New Yorkers, pointing to those challenges as an explanation for the criticism that has buffeted his administration. The press office has undergone shifts in personnel and new hirings, including at least two rounds of changes since last May, when Ms. Hinton was brought in — filling a post that had been empty for three months.

The administration’s inability to define itself has been highlighted by the weeks of unforgiving headlines that have accompanied news in at least five investigations, including inquiries by the United States attorney for the Southern District of New York and the Manhattan district attorney’s office. Ms. Hinton’s letter to the mayor, dated April 6, came before the revelation of most of those investigations.