For the past decade, Microsoft has largely ignored the Web as an emerging platform for application development with fears that it could render Windows obsolete. But that will all change next week, as Microsoft unveils a new strategy for transforming its Web properties into an open platform for developers.

The shift is a direct attack on Google, which has dominated the online space using that very same technique. Most of Google's offering, from its Search to Maps service to Desktop Sidebar all provide methods for third parties to extend -- and improve on -- the technologies.

As part of its new "Web platform" strategy, Microsoft will expose application programming interfaces, or APIs, for MSN Search using SOAP. Third party applications will be able to access up to 10,000 search results per day. Microsoft's Desktop Search API will also be opened up to outside developers.

Google and Yahoo have long offered access to their search APIs and both companies recently opened up their mapping services, which can be extended by developers for specific uses such as finding cheap gasoline or embedding directions into a Web site.

Microsoft is responding by giving developers free access to its MSN Virtual Earth service using JavaScript. MSN Messenger will also be opened up for companies to extend the communications service. For example, a company could create an add-on that automatically translates instant messages as they are sent.

Adam Sohn, a director in the marketing group at MSN, said on Thursday that Microsoft recognizes its platforms will have more value if more applications are built upon them. And the only way to encourage the development of such applications is to open up the technology to outsiders through APIs and other tools.

One of those tools, code-named "Atlas," will debut next week at Microsoft's Professional Developers Conference in Los Angeles. Microsoft will also discuss at the PDC ways developers can extend its new Start.com RSS aggregator.

At the core of Atlas lies the MSN Framework for building applications atop Microsoft's Web properties such as the next version of Hotmail and MSN Spaces. The object-oriented JavaScript framework will enable Microsoft developers to more quickly build features into MSN sites. Atlas will also closely be tied to ASP.NET 2.0 and Avalon, the presentation framework in Windows Vista.

But because many Web 2.0 applications reside in the Web browser, the underlying operating system essentially becomes irrelevant. That shift could pose a significant risk for Microsoft, analysts say, as the world becomes more connected and less reliant on desktop-only services.

Sohn, however, downplayed the risk to Microsoft's core Windows and Office businesses. He explained that Windows-based clients would be able to take advantage of the MSN platforms just as easily as those on the Web. Windows Vista, for example, will include native support for RSS and encourage the development of "connected" applications.