The Federal Trade Commission may be preparing for a legal fight over Google’s planned acquisition of mobile ad company AdMob, according to a report in the Wall Street Journal. The deal has been held up for months as the FTC reviews it for antitrust violations.

The report says the FTC has sent letters to AdMob competitors asking for sworn statements on the potential impact of the deal, and that the commission has already briefed Congress about its concerns. While the WSJ said the FTC hadn’t yet decided on how to rule the case, Reuters cites an anonymous source who claims the FTC is “prepared to make a recommendation sue.”

Meanwhile, Apple is preparing to announce its own mobile ad platform on Thursday when it unveils iPhone OS 4, according to AllThingsD. Apple bought AdMob competitor Quattro Wireless in January for $275 million. Google previously ponied up $750 million for AdMob, likely to prevent Apple from grabbing it first.

Given the FTC pressure, Google couldn’t be happier about the imminent competition from Apple in the mobile space. One wonders whether the timing of the two events was one of the topics discussed at the obviously staged meeting between Eric Schmidt and Steve Jobs two weeks ago. Apple’s suit against HTC, launched at the beginning of March, was a thinly veiled attack on Google Android. Apple’s ironic helping hand this week could be a gesture of conciliation towards Mountain View.