AN FRANCISCO, Sept. 17 — Sun Microsystems plans to throw its weight behind the "open source" software movement on Wednesday as part of an industry effort to offer an alternative to Microsoft's Windows and Office programs.

Sun's challenge, based on the Linux alternative to Windows-based software, is a daunting one, according to industry analysts, because Microsoft's Office suite of word-processing, spreadsheet and other software applications is pervasive in the corporate computing world.

Yet Sun executives said they believed that Microsoft was vulnerable in cost-sensitive markets like large corporate call centers, which provide things like customer service; retail banking organizations; and government and educational institutions.

"The industry is ready," said Jonathan Schwartz, executive vice president for software at Sun. "There is a great opportunity for a major systems company to commercialize a full Linux desktop." Sun plans to promote the Linux operating system along with Sun's own line of StarOffice applications programs.

Mr. Schwartz said Microsoft was also at risk because many organizations were frustrated with computer security issues that continued to plague the company's software.

Sun, which plans to announce the new strategy at a conference for its customers on Wednesday, said it would begin shipping the new products in the next nine months.

Although the Linux operating system for file-sharing server computers has proved a viable alternative to Microsoft and other vendors in the price-conscious part of corporate computing, Linux has not yet made significant inroads among nontechnical personal computer users.

But a number of executives who are involved with open-source software said that Linux was beginning to catch on among the nontechnical users. One reason for that, they said, was that Microsoft had changed its pricing for corporate and government organizations in recent months to a subscription model, which many customers say has effectively raised the cost of the company's software.

"When Microsoft changed their pricing policy for enterprise customers," said David Patrick, the president and chief executive of Ximian, a partner of Sun, "it sent a strong message. And since then our activity has increased exponentially." Ximian publishes open-source software, including Gnome desktop applications and Ximian Evolution, a competitor to Microsoft Outlook.

For Sun, a computer maker and software company that has been struggling along with the dot-com and telecommunications industries, offering an inexpensive alternative to Microsoft's products is an effort to find new customers.

Mr. Schwartz argues that besides having lower licensing fees than Microsoft, the open-source alternative based around Linux and Sun's own StarOffice program will also offer other indirect cost savings.

"We can support 2,000 users with one system administrator at Sun," he said. "It requires in the neighborhood of one administrator for every 50 users in the Windows world."

But he said Sun had no immediate plans to try to compete with Microsoft for the heart of its user base: white-collar workers and managers.