Mayor Gavin Newsom and the United Nations are eyeing a former naval shipyard contaminated by radiation, heavy metals and other industrial toxins as the future site of a sprawling new green technology complex and climate change think tank.

The proposal would turn a section of the Hunters Point Shipyard, one of the most polluted places in the nation according to the U.S. Environmental Protection Agency, into a UN "Global Compact Center" meant to help solve the world's pollution dilemmas and foster clean tech business.

The city hopes to start construction on the center in 2011 and open its doors in 2012. But the project faces many hurdles before it can be realized, including the completion of a complex environmental cleanup, the approval of the city's Board of Supervisors and finding investors.

The U.S. Navy, EPA and state regulators have been working to clean up toxins from the site since the early 1990s and have spent more than $500 million so far. Once finished, the land would be transferred to the city.

"Our current schedule is that the land will be ready to transfer to the city of San Francisco in the middle of 2012," said Mark Ripperda, EPA's project manager for the site. "Timelines can always be changed, but that schedule is pretty solid."

That makes the city's planned 2012 opening unlikely, but officials said the Navy could allow some construction to start before regulators finish their work.

The parcel of land the UN center would occupy would have more than two million square feet of commercial space in a campus-like setting, with views across the bay and to downtown San Francisco. The site would feature a conference center, UN office buildings and have an estimated cost of at least $20 million.

"California, in general, and San Francisco, in particular, has been at the forefront of environmental sustainability and justice for many years and all of the right ingredients are here," said Gavin Power, deputy director of the UN Global Compact.

The shipyard is located next to Candlestick Point, the current home of the San Francisco 49ers, who are planning to leave the city for a new stadium being planned down the peninsula, in the city of Santa Clara.

On Thursday, the same day the mayor announced the proposed UN center, Santa Clara released an environmental impact report for the 49ers' new stadium, moving the team one step closer to leaving.

Newsom has been clear in his desire to keep the 49ers in San Francisco, and the timing of his proposal for a new, high-profile tenant at the site made clear the city is planning to move on with or without the team.

"If the Niners come, they are perfectly compatible," said Michael Cohen, the mayor's director of economic and work force development. "If not, the 25 acres dedicated to the stadium site can be used for a range of alternative purposes."

The UN Center and a future stadium would be key parts of San Francisco's plan to redevelop the Bayview-Hunters Point neighborhoods, a project Cohen called "the most important development project in city history."

Voters have approved the redevelopment plan, which is expected to create more than 10,000 new homes, parks and retail space.

The idea that the shipyard would finally be cleaned up led some members of the Hunters Point-Bayview community to greet the proposal with open arms.

"Environmental justice entails not just having the shipyard cleaned up, but also revitalizing to create jobs and parks and affordable housing," Veronica Hunnicutt, chair of the mayor's Hunters Point Shipyard Citizens Advisory Committee, said in a statement.