Austrian far-right leader Joerg Haider believes that a "no" in France's referendum on the EU constitution Sunday would help him force a popular vote on the treaty, his spokesman said.

"If the French say 'no' then that will strengthen our case," Stefan Petzner told AFP.

He said Haider planned to petition the Austrian constitutional court as a private citizen to block the treaty which was ratified earlier this month by both houses of the Austrian parliament.

An earlier attempt by Haider to approach the court in his official capacity as the governor of the southern province of Corinthia failed because he did not get the support of his coalition partners.

Haider, who has built his career on anti-European invective, in April seized control of the junior party in the national government, renaming it the Alliance for Austria's Future.

Petnzer said the planned court bid to block the constitution "will take a very long time, three to four years we think.

"If the French reject the constitution it will really help us because it will block the whole process," he said.

Austrian Chancellor Wolfgang Schuessel refused to call a referendum and said earlier this month that 60 percent of Austrians supported the treaty.

Petnzer said Haider plans to contest the ratification of the EU constitution whatever the outcome of French referendum.

Austria on Wednesday ratified the EU constitution treaty, with members of the upper house of parliament voting overwhelmingly in favour.

Legal experts have said the ratification is final and cannot be overturned.