Yarone Zober's appointment as deputy mayor could be anything but temporary.

After the latest setback in his recovery from cancer, Mayor Bob O'Connor may not be able to resume his duties for some time, and earlier hopes that he could be back at his desk next month appear to be all but gone.

During a news conference yesterday, Dr. Frank Lieberman, chief of neuro-oncology at UPMC Hillman Cancer Center, said Mr. O'Connor was in no position to resume his duties after undergoing surgery Sunday to remove a buildup of fluid in his brain.

"I don't think he's cognitively at a point where he can be expected to resume his duties and that's why a deputy mayor was appointed," he said.

While doctors said Mr. O'Connor showed a "dramatic improvement" after the surgery and was sitting up in bed, talking and eating yesterday, Dr. Lieberman acknowledged that the mayor was not lucid enough to take back the reins of government, which were handed to Mr. Zober Sunday before the surgery.

Neither he nor other members of Mr. O'Connor's medical team would venture to predict just how long it would be before the mayor could resume his duties, let alone return to City Hall.

"I think the wisest thing for us to say is that we're really going to have to take it for right now day by day and then I think week by week," Dr. Lieberman said.

While the initial hopes were that the mayor could be able to return to City Hall by early September, Dr. Lieberman said that it now could be longer than that, given the complexities of Mr. O'Connor's illness.

In the aftermath of Sunday's surgery, Mr. O'Connor's physical therapy has been put "on the back burner right now," said Dr. Stanley Marks, director of clinical services at the cancer center.

Mr. O'Connor, who was scheduled to undergo his third methotrexate treatment yesterday for primary central nervous system lymphoma, also has been experiencing side effects from medications, including fatigue.

Members of the mayor's senior staff decided to appoint Mr. Zober, the city's policy and general services director, as deputy mayor once it became evident that Mr. O'Connor would need surgery Sunday.

Mayoral spokesman Dick Skrinjar said Mr. O'Connor had prepared a letter in advance to designate Mr. Zober as deputy mayor in the event he was unable to perform his duties. The only thing missing was the date.

Mr. Skrinjar said that when doctors told members of Mr. O'Connor's staff the mayor would be temporarily disabled by the surgery, Dennis Regan, Mr. O'Connor's chief of staff, called Solicitor George Specter, who said a deputy mayor should be appointed.

It is believed to be the first time since the 1974 adoption of the city's home rule charter that the optional provision allowing for the appointment of a deputy has been triggered because the mayor has become disabled. It has been invoked at other times in routine instances when mayors have traveled out of town.

City Council members accepted the one-paragraph letter signed by Mr. O'Connor and witnessed by his son and daughter at their meeting yesterday, their last until September.

Mr. Skrinjar said the contingency plan was put into effect before the firings last month of three top mayoral aides: Chief of Staff B.J. Leber, Solicitor Susan Malie and Finance Director Paul Leger.

The purge was triggered at least in part by perceptions by some loyalists to Mr. O'Connor that dissident staff members were trying to block Mr. Zober's appointment as general services director, a post that would make him eligible to be appointed deputy mayor.

During a telephone interview yesterday, Mr. Zober, once an aide to former City Council President Jim Ferlo, who is now a state senator, said he did not believe the controversy would have any impact on his ability to carry out his duties as deputy mayor.

"That's history," he said. "What's past is past. We're looking forward and moving in the direction Mayor O'Connor wanted when he appointed all of us."

On his first day as deputy mayor, Mr. Zober signed several Weed and Seed contracts. He said he was "honored and humbled that Mayor O'Connor would think of me and have faith and confidence in me to fulfill this role."

He also called it a sad time, adding the first thing he did after being notified that he would be appointed deputy mayor was to head to the hospital to see Mr. O'Connor.

"No one would be happier to see the mayor recover as soon as possible than me," he said.

As with other members of Mr. O'Connor's staff, he refused to speculate on how long he would be deputy mayor.

"We're just taking it one day at a time, as are Mayor O'Connor and his family," he said.

Mr. Zober vowed to carry on Mr. O'Connor's agenda, listing as his priorities the mayor's clean and safe program, his "redding up" campaign, and his business initiatives, including efforts to revitalize the Fifth and Forbes corridor Downtown.

City Council members saw Mr. O'Connor's absence, even if extended, and the appointment of Mr. Zober as deputy mayor as having little impact on the operations of the government.

"The function of government will go on. It is seamless and it is lawful," Councilman Doug Shields said.