Clay Armbrister, Mayor Nutter's chief of staff, a quiet presence who helped steer the city government through fiscal crisis, announced yesterday that he was leaving the administration.

"I am at a point in my life where I'd like to turn a page," said Armbrister, who expects to stay on through most of the city budget process, which should take another few weeks.

Suzanne Biemiller, director of policy, planning and coordination, will take over as interim chief of staff. Nutter said he'll launch a search to find a permanent replacement.

Nutter called Armbrister's departure "bittersweet," and praised his steady hand during the city's financial problems.

"He is out front when he needs to be, but I have never met a more selfless person," Nutter said. "The one thing we all know about Clay is that he will do what needs to be done to get the job done."

Armbrister was hired by Nutter before he took office in 2008. Though not part of Nutter's political inner circle, the two graduated from the University of Pennsylvania in 1979 and had known each other for many years. Armbrister previously served at Temple University as chief operating officer and did stints as city treasurer and managing director of the Philadelphia School District.

Armbrister said he had some trepidation about taking the job, but when the city plunged into financial deficit in late 2008, forcing a series of painful cuts, he knew he was in the right spot.

"I then found my purpose," he said. "I said this is the place I think I'm meant to be, to help guide this."

Armbrister did not reveal his post-City Hall plans, but said he was in talks about a job.

Considered a behind-the-scenes force, Armbrister has not played the same public role as Mayor Ed Rendell's longstanding chief of staff, Comcast CEO David L. Cohen, who wielded great authority and often acted as Rendell's alter ego.

Armbrister's announcement follows the departure of a series of Nutter's original hires. Managing Director Camille Barnett, Deputy Mayor Andrew Altman, Budget Director Steve Agostini and Press Secretary Doug Oliver all departed before this year.

Biemiller's salary will be raised from $118,750 to $178,650 for the interim job.