Austrian lawmakers will vote in May on whether to ratify the new European Union constitution, under a law adopted Wednesday that set the month but not yet the specific date for the parliamentary poll.

The treaty must receive a two-thirds majority in both houses to be ratified, though observers said they expected Austrian lawmakers to give it the required backing.

Austria is among about half the EU countries who have opted to submit the treaty to a parliamentary vote, rather than a popular referendum.

Conservative Chancellor Wolfgang Schuessel again told lawmakers he regretted that the new text was not being put to a pan-European referendum in all 25 EU states, but ruled out a separate referendum in Austria.

"The fact that the European constitution will be ratified in only a few European countries, and not in all 25 is a bit unsatisfactory," he said.

All 25 European members must approve the constitution, designed to streamline the workings of the enlarged European Union, before the end of October 2006 in order for it to take effect.

Late last month, Spain was the first member of the bloc to put the first-ever EU constitution to its citizens, who gave it a resounding seal of approval although turnout was low.

Lithuania, Hungary and Slovenia have already ratified the text.