Mark Alan Hughes, hired nearly a year ago to the day, said yesterday that he was stepping down as Mayor Nutter's hand-picked choice to create and lead Philadelphia's first Office of Sustainability.

"It's time to breathe and think and write. There's just not time in government for that kind of stuff," said Hughes, who described himself "an academic at heart."

At the same time, he said, "this is a government that is fully activated on the 'green' agenda. Everyone has really embraced it."

Hughes said he had no immediate plans.

His departure, scheduled for June 18, establishes Hughes as the second member of Nutter's inner circle to leave.

Wendell Pritchett, Nutter's policy director and deputy chief of staff, resigned in August to resume teaching at the University of Pennsylvania law school. In April, he was named chancellor of Rutgers University's Camden campus.

A third Nutter aide, senior adviser Pauline Abernathy, began a four-month leave May 11 to work at the Institute for College Access and Success.

Hughes' departure stands apart, though, because his hiring marked the fulfillment of a campaign promise for Nutter. With a salary of $142,500, he reported directly to the mayor and Chief of Staff Clay Armbrister.

Hughes oversaw an office with six employees, including himself, and a $1 million budget. He gave no hint of his plans to leave when he testified before City Council last month.

News of his exit comes just three weeks after Hughes shepherded through for Nutter a 15-goal plan called Greenworks Philadelphia, which charts a path for building the nation's No. 1 green city.

Hughes was also Nutter's point person on the federal stimulus funds that Philadelphia will soon receive, joining the mayor in trips to Washington to lobby Congress and White House officials about how the money should be spent.

"On sustainability and the Recovery Act, Mark has done what he came here to do," Nutter said in a statement. "He has put in place a foundation and a set of plans that will guide us to success. Of course we will miss Mark, but my sense is that he will never be far away and always available if we need him."

Mayoral spokesman Luke Butler said he did not believe Hughes' departure was unexpected. "Mark was brought in initially on the sustainability side to pull together the framework to coordinate all of the various different initiatives," he said. "That kind of moves into the implementation phase now."

It was unclear yesterday whether Nutter would appoint a new sustainability director. "We'll make an announcement in coming weeks on exactly where or how that responsibility will fall and about who will oversee the implementation and coordination of Greenworks," Butler said.

The administration is also expected to soon announce the hiring of a "recovery officer," to be paid with federal stimulus funds, to oversee local spending. The city issued a request for proposals in search of such a person two weeks ago.