Treasure Island, a former U.S. Navy base, was signed, sealed and delivered to San Francisco on Tuesday.

Well, almost.

The official transfer of the man-made island in the middle of San Francisco Bay from the Navy to the city will have to wait until environmental reviews are completed. Final project approvals and the actual transfer are expected this spring.

But after negotiations that spanned three presidencies, Speaker Nancy Pelosi, Mayor Gavin Newsom and Navy Secretary Ray Mabus signed a transfer agreement on Tuesday that includes payments to the Navy that could top $105 million, funded by private companies and revenue from developing the island into a model 21st century neighborhood.

Mabus called the deal a template for future base handovers.

"The transfer of Treasure Island is a win for San Francisco, it is a win for the state of California, a win for the United States Navy and a win for the American taxpayers," Mabus said.

The city and Navy have disagreed since 1993 over the worth of the 400-acre island.

"For 17 years the Navy and city have not been able to agree on the actual contract for the transfer of the property," said Jack Sylvan, the point man on the project for the mayor's office. "Now we have fully negotiated that agreement."

The development plan calls for a veritable ecotopia with about 8,000 homes, a 60-story skyscraper, three hotels and 300 acres of open space. A new ferry terminal and shuttle buses would connect the community with the city. The neighborhood would tap wind, solar and perhaps tidal power.

The plan includes measures to make the island seismically safe and guard against projected sea-level rise. The mayor hopes to see construction start by this time next year.

So what could go wrong?

"If there was an earthquake tomorrow and half the island was underwater," Sylvan joked, "then we'd have to figure something out."