SAN FRANCISCO (Reuters) - Google Inc said on Monday that it was acquiring of AdMob, one of the largest mobile advertising networks, for $750 million, widening its bet that cell phone advertising could become the Internet's next-big money maker.

Google's agreement to buy AdMob in an all-stock deal would give it a key asset as it seeks to extend the reach of its online advertising business from the tethered world of PCs to the smartphones that consumers increasingly use to access the Web while on-the-go.

Google's free Android operating system already provides the basic software that powers many of the newer phones, including the recently released Motorola Inc Droid, and which compete with Apple's popular iPhone.

Privately-held AdMob makes technology for serving graphical, display ads on mobile phones and maintains a network that allows advertisers to place display ads on mobile Web sites and directly within specialized smartphone applications.

The current revenue opportunity is still modest by Google's standards - J.P. Morgan analyst Imran Khan pegged AdMob's annual revenue at $45 million to $60 million - but analysts said the deal underscores Google's belief that the market is set to grow.

"They've made it pretty clear that mobile is one of the biggest opportunities they see," said UBS analyst Brian Pitz.

The deal appears to represent the third largest acquisition in Google's history, behind the 2008 acquisition of DoubleClick for $3.1 billion and the Google's 2006 acquisition of YouTube for $1.65 billion.

In an interview with Reuters, Google executives declined to say whether the deal would have a positive or negative impact on Google's profitability, or provide details about revenue expectations.

"We expect this will accelerate our growth in this space," said Google Vice President of Corporate Development David Lawee.

Google, the world's No.1 Internet search engine, does not disclose how much of its revenue, which totaled nearly $22 billion in 2008, comes from mobile ads.

Last month, Google said its mobile searches increased 30 percent quarter-over-quarter in the third quarter.

Google executives said they expected the acquisition to be subject to regulatory review, though they said they don't foresee any concerns blocking the deal, which the company said it expects to close in the next several months. Continued...