It’s suddenly a lot harder for venture capitalists and startups to raise funds, as investors fed up with low returns turn their backs on the sector.

Most industry observers agree that lots of young firms will simply not be able to raise their next round of funding, commencing a period of belt tightening, consolidation and closures. At a minimum, it seems to mark the beginning of a more level-headed investment climate in Silicon Valley, after years of insatiable lust for all things mobile and social.

But if the drop-off is too sudden and steep, this new austerity could spill over into an economy highly dependent on the tech sector. Indeed, as The Chronicle reported last week, the industry has an enormous impact, with each tech job creating 4.3 indirect jobs in the community, according to a Bay Area Council Economic Institute report.

The investors and venture capitalists I spoke to insisted that we’re not on the verge of anything like the dot-com meltdown, characterizing the shift as a minor and healthy correction, or a “rationalization.” One suggested it was little more than the usual process of separating good and bad ideas in the marketplace.

But the numbers suggest something new is afoot. In the third quarter, the amount that U.S. companies raised in venture capital dropped 32 percent from the prior year, according to Dow Jones VentureSource. Venture capital funds themselves raised 17 percent fewer dollars from the second to third quarter, even as the number of funds grew, according to a joint report from Thomson Reuters and the National Venture Capital Association.

Economic uncertainty

Some partially blame the economic uncertainty surrounding the outcome of the election and the “fiscal cliff.” But the main problem seems to be that many of the “limited partners” that fund venture capital are pulling back after years of frustration.

Ever since a brief period in the late 1990s when venture capital burned bright, the industry has been delivering consistently weak returns on the whole.

In fact, despite requiring greater risks and larger capital outlays, venture capital has been underperforming the stock market over the past decade, according to a report this year by the Ewing Marion Kauffman Foundation.

Joe Dear, chief investment officer for CalPERS, told Reuters this summer that venture capital “has been the most disappointing asset class over the past 10 years as far as returns.” The huge pension fund for California’s public employees didn’t return repeated calls from The Chronicle.

Investment horizons have steadily spread out, from five to 10 to sometimes 15 years, as exit opportunities like acquisitions and initial public offerings fail to materialize. This has sometimes forced investors to put in more money to protect their initial funds.

‘Pretty grumpy’

“The industry definitely, for the last decade, has been a tough place to be,” said Ray Rothrock of Palo Alto venture capital firm Venrock. “We’re all pretty grumpy right now.”

Some of this is due to macroeconomic conditions outside the control of venture capitalists, notably the housing and banking crises. But at least some of it has to do with poor picks and herd mentality, funding companies with few real prospects and driving up the entry price for legitimately promising companies beyond what they could pay off.

“The market overfunded the number of companies in the system,” said Hans Swildens, founder of Industry Ventures in San Francisco. “There’s a glut.”

Even the grand promise of Web 2.0 companies that lured so much recent money hasn’t generated the hoped-for returns. The ones that managed to go public were often disappointments, including Facebook, Zynga and Groupon, in some cases leaving late-stage investors underwater on their holdings.

That was a final straw for some.