The San Francisco 49ers on Friday acknowledged that the battered economy likely will slow down their plans to build a new stadium in Santa Clara and now has them willing to discuss a once unthinkable option — sharing a new home with their cross-bay rival, the Raiders.

Combining resources with the Oakland Raiders — as the New York Jets and Giants have done on a new $1.6 billion stadium — may be the only way for the 49ers to overcome frozen financial markets to fund a new stadium, NFL insiders and sports economists say.

Team officials said Friday that they remain focused on starting construction of a new $854 million stadium in 2010, but acknowledged the economy and other factors “are making hitting our target more difficult.” While there are no immediate plans to join forces with the Raiders, the 49ers would be willing to discuss sharing a stadium “if a workable option emerges.”

Given the disruption of the bond markets and the 49ers’ continuing impasse with the Ohio company that controls the land where the 68,000-seat stadium would be built, the team’s plan to begin construction next year for a 2012 opening is almost certainly defunct, sources said. Santa Clara Mayor Patricia Mahan said the recession could force Santa Clara to pare back its financial investment of up to $136 million in redevelopment money in the project.

Considering the dramatic run-up in stadium construction costs in recent years, the 49ers’ plan to finance a stadium alone, with a smaller government subsidy than many NFL teams have received for stadiums which cost much less, was always a difficult project.

But the economic collapse of the last six months has pushed that plan to the brink of impossibility — at least temporarily, say investment bankers who have financed NFL stadiums, sports economists who study the league’s finances, and NFL team officials who spoke on condition of anonymity.

The 49ers are contending with many obstacles: the effect of the recession on big corporations that would buy naming rights and luxury suites, uncertainty over the future of the NFL’s stadium finance program, and the fact that almost every team outside California has already built a new stadium.

“There is no question that new stadium projects are difficult to accomplish in California and the current economic climate creates new wrinkles that we have to work through,” said Lisa Lang, a 49ers spokeswoman. “But we have an ownership group that is spending significant resources each month to make this goal a reality, and we are pushing forward despite the economic factors.”

The good news, Lang said, is that the 49ers are focused on environmental studies and negotiating a deal with Santa Clara now, and are not yet seeking financing.

“Our hope is that once we begin the financing phase, the credit markets will have recovered and we will be able to finance our project,” she said.

None of that means the 49ers’ stadium ambitions in Santa Clara are dead.

The economic picture could be very different a year or 18 months from now, economists and bankers say. And one silver lining is that the global slowdown has blunted inflation in concrete and steel prices that had been increasing construction estimates by $25 million a year.

Ron Garratt, the assistant city manager who is Santa Clara’s lead negotiator, said the city and the team are pushing forward on a term sheet that would define in great detail the financial agreement between the 49ers and the city.

“We’re making progress,” Garratt said Friday. “We are absolutely moving toward an election this year, and a term sheet that will be coming out sooner rather than later.”

But for now, the 49ers face the worst financial climate many stadium experts have ever seen.

“Sorry to be so negative, but I wouldn’t be sanguine if I was those guys,” said Robert Tilliss, chief executive of Inner Circle Sports, a New York investment banker who has worked on numerous stadium deals, including AT&T Park in San Francisco.

Tilliss called the current market for long-term financing of a stadium project “crippled.”

Sports economist Michael Leeds of Temple University said the current downturn is hitting wealthy individuals and corporations who form the core market for premium seating, stadium advertising and naming rights, which are central to financing the 49ers stadium.

Several insiders said the economy could force the 49ers to consider what the Giants and Jets did — teaming up with their cross-bay rival, the Raiders, to build a stadium the two teams would share.

A shared stadium would generate more revenue, potentially making risk-averse lenders more likely to finance it. There is a huge wild card in that plan, however — the Raiders’ mercurial owner.

“Economically it makes sense, but you’ve got to get people to agree to live together and live harmoniously,” Tillis said. “It’s complicated. The Jets and Giants have been living together for awhile, so they know what they are dealing with, but with Al Davis in the mix, I think it’s challenging.”

Raiders CEO Amy Trask declined to comment about the possibility of sharing a stadium with the 49ers Friday, other than to say, “We enjoy our relationship with the 49er organization and wish it the best with its stadium endeavors.”

Lang said a shared stadium with the Raiders is not the 49ers’ current objective.

“However, if it makes sense to share the stadium with another professional sports team and a workable option emerges, it is something we would be willing to discuss,” she said.

By sharing a new stadium, the Giants and Jets were able to extract $300 million from the NFL’s stadium finance program, and will move into their new stadium in the New Jersey Meadowlands in 2010. But with the league’s stadium fund exhausted, a replacement finance program would have to be completed in conjunction with a new collective bargaining deal with the NFL players union — a process rife with uncertainty, especially given the death last year of longtime union president Gene Upshaw.

Also looming is a stalemate between the 49ers and Cedar Fair Entertainment, the Ohio amusement park company that owns Great America. Over the past six months, “there’s been no progress in that area,” Lang said.

A Cedar Fair spokeswoman, Stacy Frole, said the company is still willing to sell its interest in Great America to the 49ers, clearing a path to build the stadium on Great America’s main parking lot, but she agreed there has been no significant progress.

“It’s the same situation,” she said.

Mahan said the jobs that would be created by construction make the case for a stadium stronger. But the mayor said that the recession’s impact on Santa Clara may force the City Council to slow its evaluation of the proposal, even if that means the project is delayed.

“I can’t help but think,” Mahan said, “that there’s going to have to be a delay.”

Contact Mike Swift at (408) 271-3648 or at mswift@mercurynews.com.