Google's search slip is showing

(Fortune) -- New numbers point to more slowing in Google's search ad traffic - and analysts are adjusting their numbers down.

The troubling trend that first appeared in January continued last month, particularly in total search volume and in paid clicks, according to research released late Wednesday by research shop comScore.

The report says Google's February search traffic fell 4.6% below the January level and that paid clicks fell 3% for the same period. This is particularly bad news, since it confirms a trend that Google disputed last month and it also is the closest read on the pulse of Google's revenue rate.

If the comScore numbers are accurate, paid clicks are on track to be down more than 12% for the quarter.

As Piper Jaffray analyst Gene Munster points out in a report Thursday, the downward trend does not match the 8% sales growth rate Wall Street is looking for in the first quarter. Munster, along with Lehman Brothers' analysts, cut Google estimates Thursday on the basis of the report.

Piper now expects Google to report sales to be flat to up 5% over the fourth quarter, down from the 8% prior target. Lehman also cut its first-quarter estimate to about 6% citing weak consumer market and potentially lower advertising budgets.

The news knocked 3% off Google's (GOOG, Fortune 500) stock price early Thursday. The company's shares have fallen by a third so far this year.