NEW YORK – Karen Mills is leaving at the end of August as chief of the Small Business Administration even though her successor has not been nominated.

Mills, who said in February that she would be resigning, told staffers of her plans Wednesday, said Emily Cain, a spokeswoman for the SBA.

Mills had pledged to stay in her position until her successor was ready to be sworn in, but President Obama has not nominated anyone. A White House spokesman, Robert Whithorne, said in an email that he had no personnel announcements to make.

It’s also not known who will be in charge of the SBA when Mills leaves. The SBA’s second-highest-ranking official, Deputy Administrator Marie Johns, resigned earlier this year. No replacement has been named for her.

“The agency is working closely with the White House on transition plans and on the appointment of a successor,” Cain said.

Mills will be taking positions at Harvard University’s Kennedy School of Government and its Business School, said Jim Aisner, a spokesman for the business school. She will be working on the school’s U.S. Competitive Project and its entrepreneurship program, Aisner said.

Mills has been SBA administrator since April 2009, and joined Obama’s Cabinet in January 2012. She has had support from both political parties and from small-business advocacy groups for her holistic approach to helping small business. She has said the government needed to do more than guarantee loans for companies; it also needed to help struggling companies get the counseling they needed in order to qualify for loans.

Under her direction, the agency streamlined its loan process and shortened the amount of time it takes for companies to be granted loans.