Microsoft Corporation will release a free version of its dominant Office software that users can access over the web, catching up with products that arch rival Google Inc. launched three years ago.

The world's largest software maker will offer a word processor, spreadsheet, presentation software and a note-taking program with the same look and feel of their counterparts in the Office suites that it sells for personal computers.

It is the latest salvo in an intensifying war between the two technology giants. Google announced plans last week to challenge Windows with a free operating system. Microsoft introduced a new search engine, dubbed Bing, last month, that has taken a small amount of market share from Google.

A free version of Office could hurt sales of Microsoft's top-selling and most profitable business unit. One of Office's most popular titles is a home version that sells for $150. It includes the four programs that Microsoft will give away.

Microsoft will seek to make money by using it to lead those users to its ad-supported websites, including the Bing search engine. Analysts have said that Bing's early signs of success suggest Microsoft may be rounding the corner in efforts to turn around its money-losing internet division.

Microsoft will release the free offering when it starts selling Office in 2010, it's next major release of the product, sometime in the first half of next year.