European Union leaders have ended a two-day summit in Brussels, after acknowledging their failure to agree on a new constitution for the bloc, soon to have 25 members. Negotiators were unable to bridge deep differences over how many votes each country should have in the EU decision making process.

In the end, it came down to how much power individual countries would wield, after the EU takes in 10 new members next May.

The sticking point was always whether national votes should reflect population size. That is what Germany and France wanted, and that is what the constitutional draft provided for. But Spain and newcomer Poland held out for the generous voting rights they received under a complicated mathematical formula at another EU summit three years ago. That arrangement gave each of them virtual parity with the EU's big countries, and they refused to give up their disproportionate influence.

Diplomats say the refusal by Spain and Poland to budge from their position was not the only reason for the failure of the talks. They say Germany and France were equally recalcitrant, and refused to even consider the compromise proposals offered in last-ditch attempts to resolve the impasse.

Still, Germany and France had the support of most other EU states, which were hoping to get a deal at the summit that would allow the EU to prepare itself for its expansion from 15 to 25 members next year. The bloc needs a more streamlined decision making process than the one it has now, which was drawn up when it had only six members.

The constitutional negotiations have now been officially postponed and could resume next year, when Ireland takes over the EU presidency.

EU watchers say the failure to agree on the constitution could paralyze an enlarged bloc, and lead to a two-speed Europe, with the union's original members - led by France and Germany -moving on a fast track toward deeper integration and shared policies, while the others lag behind. Indeed, the six founding members were preparing Saturday to issue a call for such a move after the collapse of the summit.

A Dutch diplomat who has attended many EU summits says he does not think the bloc will fall apart. But he says the fierce haggling on display in Brussels, and the failure to put the union's interest above national interests, will surely hurt the EU's credibility in the eyes of its citizens.