BRUSSELS, Belgium - European Union foreign ministers admitted defeat Monday in their efforts to find a constitutional compromise between countries seeking greater integration and those who fear a European super state.

Their failure after nearly two months of arduous negotiations diminished hopes for a deal on a first-ever EU constitution despite a weekend deadline for action. The ministers said the issue was so divisive it could only be resolved by EU leaders, who arrive Friday for a two-day summit.

"What we have left over now are the most serious issues for leaders," said French Foreign Minister Dominique de Villepin.

The countries also remained at odds over how to bolster the EU's defense policy without endangering security ties with the United States or trampling on some countries' cherished neutrality.

In an eleventh-hour appeal, neutral EU nations Sweden, Ireland, Finland and Austria objected strongly to a proposed mutual defense pledge, similar to NATO's stating that if one EU member is attacked, the others are obliged to provide assistance.

In a joint letter, the four said "formal binding security guarantees would be inconsistent with our security policy or with our constitutional requirements." They demanded the formal obligations be dropped.

"We're not trying to water down anyone else's commitment ... we want to be accommodating," said Irish Foreign Minister Brian Cowen.

Italian Foreign Minister Franco Frattini, who chaired the talks, said he would revise the clause for a new proposal.

De Villepin warned Frattini not to water it down, suggesting an "opt-out" for the neutrals instead. "The solidarity as expressed in this clause must not be downgraded," he told reporters.

The constitution is meant to streamline decision-making and reshape EU institutions to avoid gridlock after the 15-nation bloc takes in 10 new members, mainly from eastern Europe, on May 1. It must be adopted unanimously but Spain and Poland are threatening vetoes over new voting rules that more closely reflect national populations.

The issue is "only going to get settled by the heads of state and government," British Foreign Secretary Jack Straw said.

Poland and Spain are insisting the EU stick to a 2000 deal struck in Nice, France, that gave them 27 votes in EU decision-making, almost equal to much more populous nations such as Britain, France, Germany and Italy, which got 29 votes.

The draft constitution, drawn up earlier this year by a 105-member constitutional convention, proposes that decisions be adopted if at least half the EU states representing 60 percent of the bloc's population are in favor.

German Foreign Minister Joschka Fischer said "a bad deal was not an option," suggesting Germany would hold fast in defending the draft's call for greater integration against those afraid of ceding too much power to Brussels. "We need a decision that will ready the EU for the challenges," he said. Fischer's French counterpart agreed. "If ambitions are not high enough, maybe we should give ourselves more time," de Villepin said. "We cannot accept a text which is not ambitious."

If EU nations manage to adopt a constitution, it will have to be ratified by parliaments and referendums, with the aim of having the new charter take effect starting Jan. 1, 2005.

The 10 states joining the EU in May are Poland, Hungary, Lithuania, Estonia, Latvia, Slovakia, Slovenia, Cyprus, Malta and the Czech Republic.

CAPTION Slovenia's Foreign Minister Dimitrij Rupel, left, gestures while speaking with Bulgarian and Swedish counterparts Solomon Passy, center, and Laila Freivalds during a meeting of EU foreign ministers at the EU Council building in Brussels, Monday Dec. 8, 2003.