EU foreign ministers were forced to answer questions about the French threat after new opinion polls showed a majority of voters planning to vote "non" in a May 29 referendum, despite a personal appeal by President Jacques Chirac.

Luxembourg's Foreign Minister Jean Asselborn, whose country currently holds the EU presidency, said he did not want to "intervene in French affairs" but stressed that the referendum will be crucial for the whole of Europe.

"I am assuming that the French people will say yes, because the world will not wait for Europe. If France says no, it will be difficult," he added.

The constitution, which aims to streamline decision-making in the expanded 25-member European Union, must be ratified by all member states. A rejection in France, one of the EU's largest countries, would effectively kill the treaty.

But since mid-March, a string of opinion polls have all suggested that the "no" camp will win out.

Seeking to turn the tide, President Jacques Chirac launched a personal effort to persuade voters on French television Thursday night, warning that a French "no" would turn the country into the "black sheep" of Europe.

But two new opinion polls Saturday indicated opposition to the EU constitution had increased to 56 percent of voters.

French Foreign Minister Michel Barnier warned that Paris has no plan B if voters reject the EU constitution, reiterating that a "no" would seriously weaken France.

"We have put everything on the table. There will not be another constitution," he said. "There cannot be any other discussions for a very long time."

The expressions of concern clouded the second day of an informal meeting of EU foreign ministers in Luxembourg, in theory focussed on key diplomatic issues including the Middle East.

Neighbors watching closely

Dutch minister Bernard Bot -- whose country is due to hold a referendum, albeit a non-binding one, two days after the French ballot -- said EU leaders were watching the situation in France closely.

"I think we have to listen very carefully to what people are saying," he said. The Netherlands, also one of the founding members of the EU, has seen its strong support for the European bloc wane.

Denmark will also hold a referendum on the constitution, scheduled for Sept. 27.

"It is significant for all of Europe how France votes and we all hope France votes "Yes," Danish Foreign Minister Per Stig Moeller told reporters. "We see the treaty as a good treaty, which is necessary … for cooperation after the enlargement."

Expansion endangered

Slovenia's Dimitrij Rupel, whose country currently holds the chairmanship of the Organization for Security and Cooperation in Europe (OSCE), said he was "extremely worried" by the latest French polls.

In particular he said it would seriously cloud the EU's continued expansion plans, with a handful of Balkan states lining up to join the bloc.

"There is no theoretical obstacle to further enlargement," he said, noting that existing EU treaties provide the framework for more countries to become members.

"But politically this would be a disaster," he said.

Polish President Aleksander Kwasniewski, whose country was the biggest of 10 mostly ex-communist states to join the EU last year, also said a French "no" would "lead to complications."

Opponents' fears

French opponents of the EU constitution claim it will boost the "Anglo-Saxon," free-market economic model and erode their long-cherished European "social model" protecting workers' rights.

British Europe minister Denis MacShane -- whose notoriously euroskeptic country is due to hold a referendum in the first half of next year -- said he could sympathize with French leaders.

"The French have actually suddenly discovered in the last few months what I've had to live with almost my entire life in British politics: the mythologizing of the EU," he told reporters.

The French minister insisted public opinion in his country can still be turned round. "Every French person must take responsibility. That is the choice on May 29," he said.