Brussels, Belgium ? A summit to forge a constitution for a united, post-Cold War Europe collapsed Saturday after leaders failed to agree on sharing power within an expanded European Union.

The deal-breaker was a proposal to abandon a voting system accepted in 2000 that gave Spain and incoming EU member Poland almost as much voting power as Germany, which has a population equal to those two countries combined.

European leaders sought to minimize the damage, saying talks would resume next year, but the debacle leaves the EU in turmoil as it prepares for one of the greatest challenges in its 46-year history — accepting new members from the former communist East.

The failure scuttles, for the time being, the EU’s plan for a new president, foreign minister and a greater profile on the global stage to rival that of the United States.

It also raised doubts about the bloc’s future direction and fears over its cohesion. French President Jacques Chirac and German Chancellor Gerhard Schroeder spoke of a core group of countries pressing ahead with closer integration — a scenario others warned would divide the union.

British Prime Minister Tony Blair appealed for all to respect the “essential unity of Europe.”

Blair insisted the summit failure would not delay the expansion in which Poland and nine smaller nations will join the bloc on May 1, expanding it from 15 to 25 members.

He said the differences could be overcome and the constitution adopted, but he suggested leaders would take at least several months before a breakthrough.

“My best judgment is it’s not an impossible mountain to climb, but I can’t be sure,” Blair told a news conference. “I don’t think there’s any point to rushing this before we have the basis of an agreement.”