Microsoft has lost a key vote in its quest to develop an alternative to the Open Document Format standard.

The executive committee of the International Committee for Information Technology Standards (INCITS) fell one vote shy of the nine required to approve Microsoft's Open XML standard. It voted 8 to 7 in favour of approval with one abstention.

The vote is a setback in a long-running battle between Microsoft and those who are seeking to dislodge Microsoft's monopoly hold on the desktop with internationally approved standards for office documents. The battle has pitted Microsoft against open-source backers such as Sun Microsystems and IBM, whose rival Open Document Format for XML (ODF) has gained some support among government users.

Open XML is the default file format used by Microsoft's Office 2007. ODF was approved as an ISO standard last year, a sign that it could gain traction with organisations that give preference to standards-based technology.

But recently, Microsoft has been pushing to get Open XML blessed by the ISO - seeking to have it approved by the Joint Technical Committee 1 (JTC-1), which sets technical standards for both the ISO and the International Electrotechnical Commission. Standards groups such as INCITS, which is examining the question in the US, have been debating whether or not to back this effort.

"This is going on all over the world right now, in a very bitterly contested country-by-country battle," said Andrew Updegrove, an open-source advocate and attorney with Gesmer Updegrove in Boston.

INCITS has until 2 September to decide whether it will support Open XML within the JTC-1, but this week's vote shows that this will not happen unless Microsoft can swing some voters.