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"In the 1980s inflation was the problem, and in the early 1990s there was overbuilding, but in those downturns you had a sense that we would return to a normal growth rate over time," said Tim Mahoney, who manages real estate loans at Wells Fargo Bank. "The feeling this time around is that things aren't going to improve anytime soon."

Mahoney said the belief among many lenders is that the demand for commercial space and condominiums could be "extraordinarily weak" for several more years, in large part because businesses aren't showing signs of growing or hiring. San Francisco's unemployment rate has hovered near 10 percent since June. The state figure was 12.2 percent in September, lending support to the "jobless recovery" theory.

Lenders' jaundiced view of the market, along with Bay Area construction loan delinquency rates hovering at 17 percent, means that banks and other lenders are reluctant.

Some San Francisco condo developers say that lenders won't even entertain solid projects with a high level of equity at good locations.

That's bad for developers of all sizes, including megabuilders like the Lennar Corp., which San Francisco has partnered with to develop tens of thousands of homes and commercial space at the former Hunters Point Naval Shipyard, Candlestick Point and Treasure Island.