ODF is the default file format in OpenOffice, StarOffice and an increasing number of Web-based word processing and spreadsheet applications. Though only utilized by a small percentage of users worldwide today, ODF is supported by some of the largest technology vendors, including IBM, Sun Microsystems Inc. and Novell Inc. They argue that the format's open, interoperable nature makes it suitable for groups concerned about long-term archiving of files.

ODF's chief opponent is Microsoft Corp., whose market-leading Office suite is used by more than 400 million people worldwide, according to the vendor. By default, Office applications such as Microsoft Word, Excel and PowerPoint save files in proprietary file formats owned by Microsoft, such as .doc, .xls and .ppt, respectively -- although users can also choose open formats such as Text (.txt) and Rich Text Format (.rtf).

Some experts say that users' need to remain compatible with Office formats has been key to maintaining Microsoft's market dominance. Microsoft has argued that ODF stifles its own innovation and limits customer choice. It is developing a competing format, OpenXML, that will debut in its forthcoming Office 2007. Microsoft has garnered the support of other vendors for OpenXML and is applying to ECMA International, a rival standards body to ISO, for certification as an open standard.

"We understand the Belgian government's desire to support open-standard document formats and understand that other formats can qualify over time," said Alan Yates, Microsoft's general manager for information worker business strategy. "We believe that OpenXML formats will meet the government's criteria shortly."

In Massachusetts, the controversy that followed last year's decision to adopt ODF led to the resignation of then state CIO Peter Quinn. His successor, Louis Gutierrez, last month put out a search for third-party plug-in software that would enable Office users to easily read and save files in the OpenDocument format.