Google's search share increased a half percent in March compared with February, but that's not what has financial analysts flapping their gums a day before the search giant announces first-quarter earnings.

Google, whose Internet query market share was 59.8 percent in March, also posted only a 2.7 percent gain in paid clicks from March 2007 to March 2008, according to data issued by ComScore April 15. Google made the bulk of its $16.7 billion in 2007 from paid clicks, which come from the links on its Web pages it services.

Normally, a gain in paid clicks is viewed positively, but this is the third straight month ComScore has signaled weak numbers in this area.

Indeed, ComScore's numbers also show that Google's paid clicks for the first quarter grew just 1.8 percent from the year-ago period, a huge drop from the 25 percent paid-click growth from the fourth quarter in 2007.

Where are all of Google's paid clicks going? No one knows for sure, but  ComScore and Citi Investment Research's Mark Mahaney speculated that the company's attempts to improve lead quality for advertisers and the user experience for searches contributed to the decline.

Whatever the case, the paid-click issue is top of mind for analysts heading into Google's first-quarter earnings call after the market closes April 17. Analysts expect earnings of $4.52 a share on sales of $3.61 billion, a top-line growth rate of 42 percent over sales in 2007.

Silicon Alley Insider's Henry Blodget said he believes the current consensus revenue estimates could be met with U.S. growth of 25 percent in the first quarter, down from 40 percent in the fourth quarter, which would allow for significant deceleration in the quarter.

"This 25 percent growth estimate obviously assumes that Google has seen a strong increase in price-per-click: If it hasn't, and the ComScore data is accurate, U.S. revenue will miss by a mile and Google's overall revenue will come in well below consensus," Blodget wrote April 15.

Google isn't alone in the paid-click problem. ComScore said paid clicks and search market share for Yahoo, Microsoft and AOL also fell in March, a sign that people may be searching less for items to buy in a weakening economy.

However, ComScore debunks this theory by virtue of its total search numbers. In March 2008, Americans made 10.8 billion searches, representing a 9 percent increase from February.

Regardless of Google's first-quarter numbers, Mahaney isn't panicking. He reaffirmed in an April 9 note that Google remains one of the best plays off the secular growth in Internet advertising.

Moreover, he said Google's innovation potential is creating option value in terms of the company's potential to benefit from new Internet revenue opportunities, specifically in display advertising, video advertising and mobile search.

Incidentally, ComScore said on April 16 that U.S. Internet users viewed more than 10 billion online videos during February 2008, a 66 percent gain versus February 2007. More than a third of those were viewed on Google's YouTube video property.