Dec. 19 (Bloomberg) -- Google Inc.'s $3.1 billion purchase of DoubleClick Inc. will be cleared by U.S. antitrust enforcers as early as this week, two people with knowledge of the decision said.

The five-member Federal Trade Commission is poised to approve the transaction after reviewing complaints by Microsoft Corp. and AT&T Inc. that the combination would harm competition for Internet advertisements, said the people, who spoke on condition of anonymity.

FTC approval of the transaction would help Google, owner of the most-popular Internet search engine, expand its sales of display ads that feature pictures and videos. DoubleClick also gives Google marketing customers that spend more of their budgets on multimedia ads than on sponsored text links.

``A large part of display advertising is about relationships,'' said David Hallerman, an analyst at research firm EMarketer Inc. in New York. ``That's just as much what Google has been after with the DoubleClick purchase as anything.''

The takeover still faces an antitrust review in the European Union, where competition authorities opened an in-depth investigation in November. European Union regulators said they would rule on the transaction by April 2.

``This acquisition is good for consumers, advertisers and Web site publishers, and we continue to be confident that it will be approved,'' Google spokesman Adam Kovacevich said in an e-mailed response to questions.

Privacy Complaints

The commission is preparing to announce its decision to allow the deal to proceed, said the people.

``It wouldn't be appropriate for me to comment on a pending investigation,'' said FTC spokeswoman Nancy Judy.

DoubleClick, currently owned by Hellman & Friedman, would be Mountain View, California-based Google's biggest acquisition, ahead of last year's $1.65 billion deal for video-sharing site YouTube.

Last month, two U.S. senators told the FTC in a letter that it should ``guard against the creation of a powerful Internet conglomerate.'' Google Chief Legal Officer David Drummond said the companies are ``complementary businesses,'' not competitors.

The FTC also received complaints that the acquisition, announced in April, would endanger privacy by enabling Google to better track consumers' Internet viewing habits.

Google rose $4.02 to $677.37 at 4 p.m. New York time on the Nasdaq Stock Market. The hares have gained 47 percent this year.

Booming Market

Advertisers will bolster online spending 22 percent next year to $49.5 billion and an additional 48 percent to $73.1 billion by 2011, according to PricewaterhouseCoopers LLP. That compares with average annual growth of 5.4 percent over that stretch in the overall advertising market, the firm estimates.

In October, Google started letting Web sites run YouTube videos and related ads alongside articles, seeking to make money from a site that's popular for letting users create and watch homemade clips. Google also began selling so-called gadget ads, which broadcast live news and show movie previews.

Google's competitors have also gotten bigger. Microsoft bought AQuantive Inc. in August for $6 billion and created an online advertising group. Time Warner Inc.'s AOL unit has announced purchases of four advertising companies this year, including Quigo Technologies Inc. last month.

To contact the reporters on this story: James Rowley in Washington at jarowley@bloomberg.net; Ari Levy in San Francisco at alevy5@bloomberg.net

Last Updated: December 19, 2007 16:31 EST