It was a classic piece of public relations counter programming.

Just hours before Google (GOOG) was scheduled to unveil the Nexus One, its best answer to the iPhone, Apple (AAPL) announced that the number of iPhone applications downloaded from its App Store had passed the 3 billion mark.

The company did not say when that milestone was reached, but its CEO did seize the moment to do a bit of self-serving crowing.

“Three billion applications downloaded in less than 18 months — this is like nothing we’ve ever seen before,” said Steve Jobs in a prepackaged statement. “We see no signs of the competition catching up anytime soon.”

The press release was the latest in a series of rapid-fire news leaks and releases out of Apple headquarters — a place famous for holding its cards close to its chest.

On Monday afternoon, the technology press was consumed by a report in the
Wall Street Journal
that Apple had started briefing outsiders with details about its much-talked-about tablet computer, including pricing, dimensions and some key dates (Jan. 27 unveiling; end of March shipping). See here.

Then, later that night, All Things Digital, another News Corp. (NWS) property, reported that Apple was set to purchase the mobile advertising company Quattro Wireless for $275 million, with an announcement to follow as early as Tuesday.

If Apple has any more news to unload, it had better do so quickly. Once Google’s smartphone is out of the bag, the tech press will talk about nothing else for at least a few hours.

Below: A chart showing the acceleration in downloads since the App Store was launched 18 months ago.

[Follow Philip Elmer-DeWitt on Twitter @philiped]