In a best-case scenario, the plan's revenues would cover its costs in the first year, Legislative Analyst Elizabeth Hill wrote in her review released Tuesday evening. However, by the fifth year, she estimates the program's annual costs would exceed revenues by $300 million.

If health care premiums were to exceed the $250 a person level that proponents estimate by an additional $50 per person, Hill wrote, the deficit could reach nearly $4 billion by the fifth year.

The plan includes a mandate on all Californians to carry insurance, although it would provide free or subsidized coverage to lower-income earners. Still, critics worry that some lower- and middle-class families will be stuck with deductibles and co-payments they can't afford.

[Democrat, Sen. Leland] Yee said the measure would saddle working families with "open-ended" health care costs. "There's no way I'm going to support that type of bill," he said.

The faltering economy and a projected $14.5 billion deficit have injected a new dose of uncertainty into the proposal's prospects, however. Supporters say the plan has its own revenue sources and would not drain the state's general fund. But questions remain whether voters would get behind a massive health care plan at the same time the state's finances are in shambles.