PARIS, Dec. 2 -- France's opposition Socialist Party voted in favor of the European Union's proposed constitution, party leaders announced Thursday, a victory for the party's moderate, pro-European wing.
About 59 percent of party members voted yes in a series of nationwide caucuses Wednesday night. Turnout was high, with 80 percent of the party's 120,000 members casting votes.
The outcome was seen as a major boost for the party's leader, Francois Hollande, who is trying to pull the party toward the political center in advance of presidential and parliamentary elections in 2007.
Laurent Fabius, the number two official in the party and a former prime minister, had campaigned against the proposed constitution, arguing that it would make Europe too capitalistic. He argued for a more "social Europe," with its traditional reliance on strong welfare states and heavy government spending on social programs.
The battle between Hollande and Fabius became a test on which direction the party would take, and it could determine who emerges to challenge President Jacques Chirac, or his successor, for the presidency. Both Hollande and Fabius are considered contenders.
The vote provided a much-needed boost for the constitution, which faces an uphill fight. About 10 countries, including France, Britain, Spain, Denmark and Poland, will hold nationwide referendums on the constitution beginning this spring, and rejection by any large country could be enough to scuttle it. Other countries are leaving the decision to national parliaments.
Advocates say the E.U., which has 25 members, needs a constitution to help the organization function more efficiently, to give Europe a legal identity on the world stage and to establish the posts of European president and foreign minister to speak for the union.
"The Socialists have served their party, their country and Europe," Hollande said after the results were announced. "The Socialists have opened the process of ratification in all of Europe."
Opponents say the constitution would give too much power to a centralized E.U. administration in Brussels.
Much of the debate, which was tinged with anti-American rhetoric, centered on what it means to be a European and whether France and Europe should feel bound to follow the free-market policies of the United States.
Special correspondent Erika Lorentzsen contributed to this report.