SEATTLE -- Microsoft Corp. is rolling out a new edition of its Office programs to businesses today, and for the first time it's adding versions of Word and other programs that work in a Web browser and will be free for consumers.

Office 2010 marks a milestone in Microsoft's efforts to keep up with an industry shift from programs that are stored on personal computers to free ones that can be accessed from any PC, over the Internet.

Microsoft must be careful not to make the free apps so appealing as to undermine its lucrative desktop software business, which accounted for 29 percent of Microsoft's revenue and 51 percent of its operating income in the most recent quarter.

The free apps will have fewer features than the desktop versions. For businesses, access to the apps is included in the regular Office licensing fees, while the consumer apps will carry advertisements.

Word, Excel, PowerPoint and the other programs that make up Office are by far the most widely used for writing documents, making spreadsheets and designing slide presentations. But when it comes to free software online, Microsoft has lagged.

When the company tried souping up Office in 2007 by adding a service that lets people store and view documents online, Google was already operating Web-based word processing, spreadsheet and presentation programs.

Those programs are generally free for consumers and inexpensive for business users.

Today, 4 percent of companies use Google Apps, according to Forrester Research.

That's still far less than the 81 percent that use Microsoft's last Office software package, Office 2007. Consumers can start buying Office 2010 or using the free Web apps in June.