By NORIMITSU ONISHI

SAN FRANCISCO — Victory in the America’s Cup of 2010 gave Larry Ellison, the tech titan who had spent hundreds of millions of dollars trying to capture sailing’s ultimate prize, the right to set the rules for this year’s regatta.

Mr. Ellison, whose Silicon Valley software company, Oracle, has made him the world’s fifth-richest man, decided to bring the race home to the postcard-perfect, television-friendly San Francisco Bay, promising a sporting event that would showcase the city and transform its waterfront. But another decision — calling for the design of extremely expensive, sophisticated and fast 72-foot catamarans that would, for the first time in the history of the 162-year-old competition, fly above the water in high winds in a maneuver known as “foiling” — immediately raised worries about cost and safety.

Now, with just weeks left before the start of competition, those worries could imperil the race’s success. Only four teams have signed up because of the costs, the smallest contingent in the race’s modern history and far fewer than the 15 organizers had predicted in selling the event to city officials hungry for its economic benefits.

As a result, civic leaders are concerned that fewer contestants will mean less interest and, with fund-raising lagging, the city might even be stuck for a significant part of the tab.

Jane Sullivan, a spokeswoman for the city’s America’s Cup project, said San Francisco would ultimately benefit from the event. But she said fund-raising had been made difficult by sailing’s lack of popularity in the United States and the sailing community’s split over the new boats.

Under longstanding rules, the winner of an America’s Cup competition, which is not held on any set schedule, is allowed to decide the next competition’s location and boat design.

Aaron Peskin, a former member of the city’s Board of Supervisors who has started an online campaign to pressure Mr. Ellison to personally cover the city’s operating costs, offered a different explanation.

“Other well-to-do, philanthropic individuals and organizations aren’t really interested in donating to the hobby of the third-richest person in the United States who’s down to his last $40 billion,” Mr. Peskin said. (Forbes Magazine estimates Mr. Ellison’s wealth at $43 billion, ranking him behind only Bill Gates and Warren E. Buffett in the United States.)

The more immediate concern is the dearth of contestants. Races to determine which nation will go up against Mr. Ellison’s defending team are set to begin on the Fourth of July, with the final competition starting Sept. 7.

Artemis, the Swedish team, has not decided whether to drop out after its boat capsized during training last month in San Francisco Bay, killing a crew member; Mr. Ellison’s team’s boat was also wrecked when it capsized last fall, though without serious injuries. The teams are considering last-minute changes, including not racing if winds are too high and sturdier helmets and body armor, to improve safety.

And so even before the first race, organizers have begun acknowledging that the design choice for this year’s yacht, known as the AC72, had been a poor one.

“There is no doubt that the AC72 was more expensive to manufacture and prepare for than we anticipated. When you couple that with the economic downturn that we experienced in 2010 and 2011, that’s the reason we have fewer teams participating this summer than we would have liked,” said Stephen Barclay, chief executive of the America’s Cup Event Authority, the company established by Mr. Ellison to run the event, adding, however, that the boats are safe.

In San Francisco, an increasingly unaffordable city where critics say the booming tech industry has been coddled at the expense of the less affluent, criticism has been rising. Much of it has been leveled at Mr. Ellison, who recently appeared at a red-carpet premiere of “The Wind Gods,” a laudatory documentary about his 2010 victory that was produced by his son, David.

“Larry Ellison made the event so big that it made it really difficult for people to put teams out,” said John Avalos, a member of the Board of Supervisors. “Maybe it’s going to result in Larry Ellison winning by default.”

Mr. Avalos, who voted for the event but now says its promoters’ claims “weren’t true or exaggerated,” recently led a hearing on the race’s economic impact. Because the number of teams had fallen to four from the organizers’ prediction of 15 in 2010, the Bay Area Council Economic Institute estimated that the event would generate $900 million in economic activity, compared with an earlier projection of $1.4 billion; attract 2 million spectators, instead of 2.7 million; and bring 6,500 jobs instead of 8,800.