European Union leaders adopted a 50th anniversary declaration in Berlin Sunday setting 2009 as the deadline for preparing a new treaty to replace its rejected constitution.

The "Berlin Declaration" was signed by German Chancellor Angela Merkel, European Commission President Jose Manuel Barroso and the President of the European Parliament, Hans-Gert Pöttering, as EU leaders looked on.

The word "constitution" was not mentioned in the two-page document at the request of many of the 27 member states, in particular Britain, the Czech Republic and Poland.

The draft constitution, designed to allow an enlarged bloc to operate, was rejected in referendums in the Netherlands and France in 2005.

In the declaration signed in the German Historical Museum on Sunday, the member nations say they are "united in our aim of placing the European Union on a renewed common basis before the European Parliament elections in 2009."

Written in the name of "We, the citizens of the European Union...," the text praises achievements such as peace and stability in Europe and sets major challenges as fighting terrorism and racism, as well as combating global warming.

It also outlines successes like the introduction of the euro and border-free travel.

EU ideals must not be taken for granted, says Merkel

Merkel said in a speech before the signing that Europe could take none of its cherished ideals -- peace and freedom, democracy and the rule of law -- for granted, and urged the bloc to get to grips with its institutional crisis.

"It must ensure that even with 27 or more member states its institutions function efficiently, democratically and in a way which citizens understand. Much is at stake," the chancellor said.

She said her experience growing up in communist East Germany had shaped her idea of freedom and justice in Europe.

"I never thought that I would be able to freely travel to the rest (of the continent) before I became a pensioner," said Merkel. "But my own experience shows that nothing has to remain the way it is."

Barroso warns against further constitution failure

Barroso urged the leaders to tackle the constitution issue soon and warned that Europe risked falling behind the rest of the world if it did not.

"A Europe of results demands efficient, democratic and coherent institutions. We must equip the European Union for globalization," Barroso said.

The declaration was the highpoint of a weekend of celebrations to mark 50 years since the signing on March 25, 1957, of the Treaty of Rome, which founded the forerunner of the EU, the European Economic Community.

After the signing, the heads of state and government were to pose for a photograph under warm spring sunshine at the Brandenburg Gate in a symbol of unity near where the Berlin Wall once divided Europe.

The leaders will then hold a working lunch focused on the themes of Europe and the future, and Europe in the world, while street festivals people throughout the German capital.

Not all work and plenty of play

As the leaders got down to the serious business of the weekend, many younger Europeans who had come to the German capital were still recovering from a night of concerts, exhibitions or clubbing.

"I've lived in Berlin for 15 years and I feel at home here," said Nicolas, a 39-year-old Frenchman at one of the 35 nightclubs open overnight. "That's what Europe is for me."

Commemorations for the 50th anniversary were held across Europe with concerts and other mainly symbolic events.