Google Inc. has bought Upstartle, the Silicon Valley-based company behind Writely.com, an internet-based word processor. The move is Google’s latest expansion away from its core search product and marks the company’s increasing interest in a market long-dominated by its Seattle-based rival.

The acquisition of Upstartle, disclosed Thursday on Google's Web site, continues the Mountain View, Calif.-based company's effort to assemble a suite of software applications that are tethered to an Internet connection instead of a single computer's hard drive.

Google didn't reveal how much it paid for Upstartle. In an analyst presentation last week, Google said it has been aggressively buying high-tech startups to deepen its product line as well as its pool of engineering talent. 

Writely, which was founded in 2004, allows users to create documents using an internet browser. The documents can be saved on Writely’s servers in formats including Microsoft’s Word and Adobe’s PDF. Users can also share documents over the internet so that nominated third parties can access or edit documents remotely.  The free service isn't currently accepting new users.

"Coming to Google will eventually give us a leg up on getting things done that we just haven't been able to with our tiny team," Writely wrote on its Web site.

Much of Google's recent buildup appears to be positioning the company to challenge Microsoft, whose dominant Windows operating system and other popular software programs influence how people use their computers. Microsoft in turn has been investing heavily to improve its search technology, hoping to lure traffic away from Google .