Google, Yahoo, and other Internet companies will feel the sting of a global advertising slowdown, an analyst said Friday.

In a research note, UBS analyst Benjamin Schachter cut revenue and earnings estimates for Google, Yahoo, and eBay for the final three months of 2008 and 2009.

“While we believe that Internet advertising will hold up better than other mediums, the macro environment will still affect Internet companies’ top lines,” he said. “The key will be how much companies can cut costs and better manage expenses.”

In afternoon trading, shares of Google edged up $1.96, or .6 percent, to $314.04, Yahoo shed $.37, or 3.3 percent to $10.78, and eBay skidded $1.05, or 7.6 percent, to $12.72.

UBS expects growth in Internet advertising spending will come in at 21.7 percent in 2008, 10.4 percent in 2009, and 13.8 percent in 2010.

Revenue estimates for Google fell from $4.3 billion to $4.1 billion in the fourth quarter and from $18.4 billion to $17.4 billion in 2009.

Earnings per share estimates were cut from $5.41 to $5.09 in the calendar fourth quarter of 2009 and from $22.69 to $21.61 for calendar 2009.

Yahoo’s fourth-quarter revenue estimate was adjusted down from $1.39 billion to $1.38 billion and earnings per share were cut by a penny to $.14.

eBay’s fourth-quarter revenue went from $2.13 billion to $2.1 billion while earnings per share were cut by two cents to $.38.

The brokerage cut its projections across all major media, with newspapers facing the bleakest 2009. UBS is projecting spending on newspaper advertising will decline 8.8 percent, while television falls 4.8 percent. The only medium with positive growth: the Internet.