San Francisco officials are racing to raise tens of millions dollars from private donors to pay for security, transportation and the other costs of hosting the America's Cup yachting championship later this year.

A spokeswoman for Mayor Ed Lee said officials have raised about $14 million of the estimated $31 million to $34 million needed to host the 55 days of racing beginning in July.

Spokeswoman Christine Falvey said Monday that the mayor has recently stepped up his own efforts to meet personally with chief executives of prominent companies based in San Francisco in an effort to meet the goals.

The city aims to pay for the event that expects to attract millions of spectators without having to dip into its general fund.

A February 2012 report by the city controller's office raised concerns that the America's Cup Organizing Committee wasn't raising funds fast enough to meet that goal.

Falvey said city officials are revisiting the cost estimates after the final event plan was significantly scaled back from original projections.

Only four racing teams rather than the dozen or so initially envisioned have paid entry fees and are planning on competing for the most prestigious trophy in competitive sailing. All four teams will be based at a single location rather than along the city's waterfront as originally envisioned.

Falvey said the mayor is optimistic that enough donations will come in to cover the cost of the event, which is expected to generate thousands of new jobs and had hundreds of millions of dollars to the local economy.

Mark Buell, who is chair of the fundraising committee, didn't return a phone call Monday.

Buell told the San Francisco Chronicle that hosting the America's Cup will still benefit San Francisco economically even if the city breaks its promise about refraining from using public money to pay for the event.

"Between the money that will come in from tourists and the crowds and the sales taxes it will generate," Buell said, "I still think that, no matter what, it will come out a boon for the city."