Until now, Microsoft has never said it would natively support ODF, promoting support through software that translates documents between Office file formats and ODF rather than native support. However, the company has been hammered by the industry -- particularly through repeated fines by the European Commission -- for its lack of support for interoperability with other companies' products, and Microsoft has made several recent moves to remedy that situation.

In an interview on Wednesday, Gray Knowlton, a Microsoft Office group product manager, said it was Microsoft's interoperability principles -- a plan unveiled last month to publish previously proprietary specifications for royalty-free use -- and the "regulatory feedback" that changed the company's mind about adding ODF support to Office.

"It came as a surprise to some people," he said of the news,"but when we outlined the interoperability principles a while ago ... those commitments were pretty real."

Knowlton said that at the time OOXML was approved, Microsoft was hearing from customers that using add-on translators for ODF was enough support. Now, however, "we've gotten that direction that people want ODF in the product," he said. "To help our business, we're happy to do that." Microsoft is facing increased pressure in the Office productivity space from competitors such as IBM and Google.

Microsoft previously had said it would support PDF in Office 2007, but Adobe, the owner of the specification, blocked that move. As a result, Microsoft said it would pull native PDF support from Office 2007 in June 2006. Adobe has since submitted PDF to the ISO as an open standard. At the same time it pulled PDF support from Office, Microsoft also pulled planned support for XPS.

IBM, an outspoken ODF advocate and critic of OOXML, said in a statement that it supports Microsoft's move, saying there is increased interest in ODF and productivity suites that support it, such as its free Symphony software, which is an Office rival now in beta.

Pamela Jones, an ardent open-standards proponent and an outspoken critic of Microsoft during the OOXML standards process on her Groklaw blog, said she had not heard that Microsoft planned to support ODF in Office. "I would be glad if it's true, though," she said.

At the same time, she noted that there are still myriad problems surrounding OOXML, so she hopes Microsoft will tend to those as well.