Advertisers in Europe and the U.S. are taking a more conservative approach online, cutting their budgets for display ads and sponsorships and shifting them to search, according to Jefferies & Co. As a result, total global online spending is going down, and the investment bank trimmed $2 billion off its global estimate for 2008.

Jefferies now believes global online advertising will grow 20% to $50 billion (down from $52 billion) in 2008, and 16% to $58 billion (down from $61 billion) in 2009. Jefferies' estimates assume online display advertising grows 14% in 2008 and just 7% in 2009.

Meanwhile, maybe search advertising really is recession-proof. Jefferies expects search to grow 26% and 23% in 2008 and 2009.

Anecdotally, Jefferies says new inquiries for advertising on the U.K., Germany, France, Spain and Italy are down as much as 30%, with "the sales process lengthening and processing costs increasing." And recent commentary from AOL, Bankrate and ValueClick leads the bank to believe that there will be no improvement in Q3.

So, add Jefferies to the list of those revising their online ad estimates. The roll call so far:

• August 27: Carat lowers estimate for total 2008 advertising growth, but bumps up online estimate
  
• August 13: eMarketer plans to drop "a few percentage points" off its March estimate of 22.7% growth
• July 7: BMO Capital Markets cuts its 2008 U.S. forecast to 1.8% from 3.6%
  
• June 30: Zenith Optimedia cuts its U.S. ad forecast for the second time in three months
  
• May 30: Lehman drops 2008 U.S. online ad forecast from 24% growth to 23%
• March 19: eMarketer cuts its 2008 online ad forecast 6%
• September 14: Oppenheimer cuts 2008 U.S. online ad estimate 26% growth to 25%