SAN FRANCISCO — Google is escalating its rivalry with Microsoft with the purchase of Quickoffice, the maker of a widely used mobile application for working on documents created in Microsoft’s programs for word processing, spreadsheets and presentations.

The deal announced Tuesday gives Google Inc. a new weapon to foil Microsoft Corp. as more people get work done on smartphones and tablet computers. Quickoffice makes those devices compatible with Microsoft Office even if the software isn’t installed on them.

Although it makes virtually all of its money from online advertising, Google already has spent several years trying to siphon sales away from Microsoft by offering its own suite of Office-like programs that are accessible over the Internet. Some of these applications, called Google Docs, are given away, while more sophisticated versions, called Google Apps, are sold by subscription for $50 a year per user.

Forrester Research analyst Ted Schadler said Google’s online applications don’t interact well with Microsoft Office files on mobile devices, a shortcoming that Quickoffice presumably will address. Schadler expects Google to add features to the Quickoffice app so it can sync with work done through Google Apps on office and home computers.

Without providing details, Google said in a Tuesday blog post that it intends to incorporate Quickoffice in its paid Apps suite.

Microsoft dismissed Google’s challenge. “Google Apps require compromise and don’t meet the productivity needs of most people and businesses,” said Clint Patterson, director of communication for Microsoft’s Office division.

It’s the second deal Google announced this week. On Monday, Google disclosed that it’s buying Meebo to help expand its Plus service for social networking.