France's Socialist Party voted in favor of the European Union's (search) new constitution, party leaders said Thursday, boosting the chances of success for a national referendum and drawing jubilant praise from pro-EU forces across the continent.

Official results were expected later Thursday, but the Socialist Party (search) said its early estimates found the referendum would pass with around 55 percent to 60 percent support. About 95,000 votes were cast Wednesday.

Rejection of the constitution by the Socialists would have made it tougher for conservative President Jacques Chirac (search) to win a nationwide referendum on the issue. Each of the 25 EU countries must adopt the text for it to come into force.

Party leader Francois Hollande, who campaigned in favor of the constitution, said he believed the "Yes" vote won.

The Socialist Party's second-in-command — former Prime Minister Laurent Fabius, who did not back the measure — conceded defeat on LCI television: "I take note of the vote, but I certainly regret it," he said.

The internal referendum was the first in the Socialist Party's history. The 120,000 eligible party members were asked simply whether they favor the EU constitution or not.

"This vote is a very important step forward for ratification of the constitution both in France and in Europe," Martin Schulz, leader of the European Parliament's Socialist group, said in a statement. He called the vote "good news for progressive forces throughout Europe."

Hollande, the party chief, backed the constitution as a way to make the EU more efficient. He warned that a "No" vote would put France at odds with Europe and particularly with Europe's major Socialist parties, all of which support the constitution.

But Fabius argued that the text is too liberal, too pro-capitalist and that it goes against what he called a "social Europe."

"Either we vote for the constitution and we will have a liberal Europe dominated by the British and the Americans," he told LCI television Wednesday. "Or we want a social Europe, and in that case, we have to vote 'No."'

After years on the drawing board, the constitutional treaty was signed last month by leaders of all EU countries.

The charter is supposed to take effect in 2007 but must first be ratified by all 25 states. Many are leaving the decision to national parliaments, but at least nine countries — including France, Spain and Britain — are putting the constitution to nationwide referendums.