* Google says received FTC second request on AdMob deal

* Says deal won't close right away

* Co. confident FTC will find deal keeps space competitive

SAN FRANCISCO, Dec 23  - Google Inc (GOOG.O) said its $750 million purchase of AdMob won't close right away as antitrust regulators seek more information about its competitive impact on the nascent mobile advertising market.

The world's No. 1 Internet search engine said in a post on its company blog on Wednesday that it received a second request from the U.S. Federal Trade Commission this week.

The FTC is asking for more information so that they can continue to review the deal, read the post, written by Google Product Manager Paul Feng.

While this means we won't be closing right away, we're confident that the FTC will conclude that the rapidly growing mobile advertising space will remain highly competitive after this deal closes, the post continued.

Google announced plans to acquire AdMob in November, in what would be its third most expensive purchase behind the $3.1 billion acquisition of DoubleClick and the $1.65 billion purchase of YouTube.

Google said at the time that it expected the deal to close in the next several months.

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.

With consumers increasingly accessing the Internet from cell phones, Google has stepped up efforts to expand into the mobile market. The company's Android software for smartphones is available on more than a dozen handsets from different vendors, making Google one of the companies best-positioned to challenge Apple Inc's (AAPL.O) popular iPhone, say analysts.

Google said it has been in discussions with the FTC over the past few weeks and that it will work closely and cooperate with the commission as it continues its review of the deal.

Shares of Google closed Wednesday up $10.56 at $611.68 on Nasdaq.

(Reporting by Alexei Oreskovic; Editing by Richard Chang)