Mayor Bob O'Connor appointed Yarone S. Zober, the city's policy director and recent appointee as general services director, to serve as deputy mayor today.

Mayoral spokesman Dick Skrinjar said the Zober appointment was made before Mayor O'Connor underwent a 30-minute surgical procedure to drain fluid buildup from his brain. The operation occurred late this afternoon, according to a statement issued by his office and the UPMC News Bureau.

Mr. O'Connor, 61, has been in UPMC Shadyside since July 10, diagnosed with primary central nervous system lymphoma. He has been undergoing treatment, which doctors earlier reported had been performing effectively against four small tumors in the mayor's brain.

The joint statement issued at 3 p.m. today said the mayor was in recovery and in stable condition.

His medical team was continuing to perform tests to determine the cause of the fluid buildup.

Mr. Skrinjar said that Mayor O'Connor's chief of staff, Dennis Regan, telephoned Mr. Zober to tell him about the appointment.

Mr. Skrinjar said members of the O'Connor administration tried to telephone City Council members when the mayor went into surgery, which occurred at about 1:45 this afternoon.

Mr.Skrinjar would not provide details of the mayor's medical situation, saying the doctors would brief the media at 10 a.m. Monday.

Previously, doctors said that Mayor O'Connor has lost so much strength during treatment that he will require intense therapy to be able to walk without help.

Mr.Skrinjar said the need for the procedure became evident late Sunday morning or early that afternoon. That's when the administration triggered the city charter provision allowing the appointment of a deputy mayor when the mayor becomes disabled.

"The doctors advised us that the mayor, because of this procedure, would have a temporary disability," he said. "They will tell us when the period of temporary disability is over. ... That's a medical decision."

He refused to speculate on the likely duration of disability.

The charter says that the mayor must inform the city clerk, in writing, when a deputy is appointed. That will be done Monday, he said.

"The city clerk doesn't work on the weekends. The city clerk and city council will get a formal letter [Monday]," he said.

Mayor's office personnel tried to contact all nine council members and directors of all city departments, he said, and left messages for those they could not reach.

He said Mr. Zober, now deputy mayor, would not be making any public statement.

"There's no anticipation that Yarone will have anything to say except that he can't wait to return to not being deputy mayor," he said.

Council does not have to vote on the appointment of a deputy mayor, but can choose the amount of a bond the individual must post while serving in that capacity. A deputy mayor has all of the powers of an elected mayor except for the power to appoint or terminate top staff.

"The staff is praying and wishing for the speediest of recoveries," Mr. Skrinjar said.