Google Inc. is shifting its strategy for its Android mobile operating system, in a bid to create a united front with smartphone and tablet makers to take on rivals like Apple Inc. and prevent wireless carriers from controlling the devices.

Google plans to give multiple mobile-device makers early access to new releases of Android and to sell those devices directly to consumers, said people familiar with the matter. That is a shift from Google's previous practice, when it joined with with only one hardware maker at a time to...