A stronger competitive landscape has forced Microsoft’s hand to reorganize its Entertainment and Devices division to formulate a response, an analyst says.

Today, Microsoft announced that Robbie Bach, president of the company’s Entertainment and Devices (E&D) Division, would be retiring this fall. Executives Don Mattrick, who oversees Microsoft’s Interactive Entertainment business, and Mobile Communications senior vice president Andy Lees will report directly to CEO Steve Ballmer effective July 1.

“I’m at the time in my life where I want to dedicate more time to my family and my nonprofit work, including my work with the Boys & Girls Clubs of America,” said Bach in a statement. “I have the utmost confidence in Steve, Don and Andy, and their ability to see through our mission of bringing extraordinary entertainment and mobility experiences to life for people around the world.”

The primary mission of E&D has been to shield the Windows PC from low-end consumer devices such as video game consoles and smartphones, but the introduction of Apple’s iPad raised the threat level a notch, said Directions on Microsoft director of research Robert Helm.

“The division’s new management will have to formulate a clear response, and quickly,” he added.

In an e-mail to employees, Ballmer signaled that the company would be cycling its resources into Office 2010, Project Natal, Windows Phone 7 and Windows Live Wave 4.

Project Natal is a codename for a new Xbox 360 input device that reads a user’s physical motions as input.

“It is a natural time for us to look ahead and make sure we have the right talent in the right roles to fuel our next set of offerings. I am confident that the changes above will set us up well for the months and years ahead,” Ballmer wrote.

J Allard, senior vice president of design and development for E&D, will also be leaving Microsoft. Allard is best known for leading the design and engineering of the Xbox console.