Newsom had been scheduled to assume his new post on Jan. 3 along with the other officials elected in November to the state's highest offices, Gov.-elect Jerry Brown and Attorney General-elect Kamala Harris, San Francisco's district attorney.
"At this point it's likely he'll remain mayor a few days longer, to conclude a few important projects" and to "ensure a stable transition for the interim mayor," Newsom spokesman Tony Winnicker said today.
Among the tasks Newsom is hoping to complete are further budget cuts to help offset an estimated $380 million deficit for the coming fiscal year, naming a district attorney to replace Harris, and the securing of the 2013 America's Cup for San Francisco.
Local team BMW Oracle, which won the cup earlier this year and is therefore entitled to choose the next host city, is still courting a bid from Rhode Island. Newsom's office is staying hopeful amid reports today that officials in that state are not ready to meet the team's Dec. 31 deadline.
Winnicker said San Francisco's bid, in contrast, is in good shape. The bid was unanimously approved by the Board of Supervisors on Dec. 14.
"It's ready to go, it's detailed, it offers extraordinary benefits for the city and the team, and we continue to believe that there's no better place on Earth for the America's Cup than San Francisco," Winnicker said. "We continue to have very positive discussions with members of the team," he added.
While Newsom is "eager to assume the office of lieutenant governor to which he's been elected," Winnicker said he is planning to delay his appointment by at least a day or two, or "at most several days."
There remains the thorny issue of naming an interim mayor to replace Newsom, a task that falls to the Board of Supervisors. That person, who needs at least six votes from the 11-member board, would serve about a year. The next mayoral election is in November.
Newsom has said in recent weeks that he was "99 percent" likely to leave office on Jan. 3, unless the board appointed a "radical" mayor who could jeopardize the city's fiscal integrity. After several hearings in November and December, the board has yet to name anyone.
The last meeting of the current board, which leans politically left of Newsom, is on Tuesday, but a new board with four new members will be sworn in on Jan. 8.
The makeup of the new board is considered slightly more moderate than the current one, which could put it more in alignment politically with Newsom.
"He's doing all he can to support the Board of Supervisors in choosing a responsible interim mayor," Winnicker said.
Newsom has said he thinks the new board should decide on an interim mayor, and that that mayor should not use the office to advance political objectives.
Winnicker declined to name any possible replacements the mayor would approve of, and added that Newsom has not yet decided on a district attorney replacement.
He said Newsom will be in Sacramento on Monday for the swearing-in ceremonies of Brown and Harris.