Shane Kim, Microsoft (MSFT) corporate vice president of Microsoft Game Studios, is saying that the overwhelming response to the test version of the Halo 3 game suggests that it will drive Xbox 360 sales when it arrives in stores on September 25.

According to the Next Generation game website, over the past four weeks 820,000 people played the test version of the game, logging more than 12 million hours of online game time. For those keeping score, that’s an average of more than 14 hours per person, or more than 30 minutes per day, every day.

“The participation in the Halo 3 beta was staggering,” Kim said in a statement. “Witnessing such a great reaction to a small portion of the game has been inspiring. It’s a testament to the fervor and anticipation that surrounds Halo 3. We’re confident that on Sept. 25 Halo 3 will drive an unprecedented wave of new gamers to the Xbox 360 platform and Xbox Live.”

The successful beta is welcome news for Microsoft, which is battling Sony’s (SNE) Playstation 3 for the affections of hard-core gamers while seeking to position itself against the surprisingly successful Nintendo Wii. The beta started off with a whimper, as bugs in the system infuriated gamers who had blocked out time to play the preview. The numbers suggest Microsoft has been able to address those issues, and deliver an experience that its core audience will find addictive.

If Halo 3 turns out to be the “killer app” game Microsoft is hoping it will be, it could pay off in more ways than one. After the sale of the console (on which Microsoft loses money or breaks even) and the game (which will cost about $60), Microsoft also is positioned to sell special accessories for game play such as wireless headsets and controllers. Then there are the subscriptions for online game play; it’s $30 for three months, or $60 for a year. (If all 820,000 beta participants had been new subscribers, that would have been $24 million in additional revenue.)

That’s not the end of the potential gravy train either. Microsoft subsidiary Massive sells advertising into online games. If Microsoft can use a game like Halo 3 to sign up gamers in droves, that increases the likelihood that it will be able to charge advertisers a premium to have their brands and products appear in the gaming environment.

We’ll see how the holiday season comes together.