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San Francisco's grand vision for a cutting-edge green community on Treasure Island is at least $60 million short of being financially feasible, despite officials' assurances that the project is supported by revenue projections.

The city's plan is $60 million to $90 million shy of the projections needed to have private developers and the Navy agree to the deal to transform the former naval base into San Francisco's newest neighborhood, The Chronicle has learned.

If unaddressed, the shortfall threatens to unravel a complex deal almost 15 years in the making. The developers and city officials both say the gap is bridgeable, but cost-cutting options discussed at a closed-door Treasure Island Development Authority board briefing this week will probably be controversial.

They include allowing developers to pay a fee in exchange for building fewer affordable housing units, delaying construction of a ferry terminal for residents, or tapping the city's police and fire department budgets to build stations for a project that was supposed to leave the city's general fund untouched.