What if Google misses?

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Tech stocks have had a wild ride so far in January, with the Nasdaq swooning dangerously close to bear-market territory. But it could get even wilder when Google weighs in on Thursday.

That’s because Google (GOOG) was a darling of the tech run-up that effectively ended in November. Like Apple (AAPL), Google inspired hope that its strong brand and innovative technology can thrive in a downturn. So just as Apple’s disappointing earnings projections spooked Wall Street, if Google delivers a surprise — negative or positive — it could send shock waves across the industry.

Unlike Apple, Google will at least have a lower bar to clear when it reports earnings. Investors fear Google’s growth will be hindered by a global economic slowdown, so its valuation has already been punished along with Research in Motion (RIMM), VMware (VMW) and other high-growth tech stocks. Google’s shares have dropped 25 percent from its mid-day high of $747, which it reached 12 weeks ago.

But despite the fall, Google stock isn’t necessarily cheap.

Google’s price-to-earnings ratio is still above 40, which suggests that investors expect the company to post encouraging numbers Thursday. (Analysts’ five-year annual growth projections for Google are in the 35 percent range, though, which suggests the stock could still be expensive.) To measure up, Google will have to turn in revenues of about $3.5 billion, and earnings per share close to $4.50. Some analysts clearly believe it can; Bear Stearns this morning boosted its revenue and earnings estimates for Google, ignoring comScore data that suggests the company’s share of the search market and recent ad click-through rates could be flagging.

Still, Google boosters might be disappointed. Online advertising fans, such as Don Dodge from Microsoft’s (MSFT) emerging business team, have suggested that the shift toward performance-based advertising, which is Google’s strength, will continue through any economic slowdown. But it’s not clear that the trend will be strong enough to keep Google’s results as high as analysts would like to see them. When Google reported fourth-quarter results last year, management said that while cost-per-click prices had dropped during the quarter as its international business expanded and U.S. advertisers hunted for bargain search terms, a strong overall holiday season kept revenues and profits high.

It stands to reason that if Google faces the same scenario this year amid a weaker overall holiday season, it might be a challenge for the company to achieve Wall Street’s revenue and earnings targets.

Not that Google tends to lose sleep over such things. The company famously chooses not to give sales and profit guidance to analysts, so Wall Street has to figure out its targets with less insight from management. This way, Google top executives say, the company won’t be tempted to manipulate its results to conform with unrealistic numbers. (Of course, that temptation arguably exists anyway, since analysts publish their targets and everyone knows what they expect.)

What does it all mean? Anything short of blowout earnings from Google and steady confidence from executives could rattle not only Google but also the whole Internet sector — though Yahoo (YHOO) has already done its part to put folks on edge. Tech investors are clearly in need of reassurance right now, and would love to get it from the big G.