BRUSSELS (Reuters) — Even though it turns 50 this month, the European Union still isn’t sure what it wants to be when it grows up.The six-nation European Economic Community created by the Treaty of Rome signed on March 25, 1957, has grown without an architect’s plan into a sprawling 27-nation union that is the world’s biggest trading bloc and covers most of the continent. A perpetual work in progress, the EU is as torn as ever between wider enlargement and deeper integration, between political unification and economic union, and between being more open to the world and protecting its manufacturers and farmers.

“European construction is not ready and will never be fully ready,” European Commission Vice-President Margot Wallstrom said this week, comparing the EU to a “jigsaw puzzle” put together piece by piece without a master plan.

Opinion polls suggest this sense of hurtling towards an unknown destination is one reason why the EU’s popularity has fallen in many member states, along with perceptions that it is too remote, bureaucratic, cosmopolitan and business-friendly.

The Union has yet to fully digest the “big bang” expansion that saw it grow from 15 to 25 member states in 2004, when most of the ex-communist states of central Europe joined what had been a wealthy west European bloc. Bulgaria and Romania joined this year, pushing the gap from richest to poorest members in wealth per capita to 11:one.

When French and Dutch voters rejected an EU constitution in 2005 intended to adapt the bloc’s creaking institutions to cope with increased membership, one factor was discontent at the eastward enlargement and fear of giant Muslim Turkey joining. Those referendum defeats triggered a crisis of confidence that lingers two years later, leaving the EU struggling on with an outdated rulebook designed for six like-minded states.

When EU leaders meet next week to celebrate the 50th anniversary of the Treaty of Rome, they will be unable to utter the word “constitution” in their solemn Berlin Declaration or give a firm date for reforming their institutions. Nor will they be able to say how much further the bloc should expand, due to divisions over whether Turkey, Ukraine and Belarus should ever be offered full membership. Eighteen countries have ratified the constitution that would give the EU a long-term president and foreign minister, a fairer decision-making system with more policies subject to majority voting, and a greater say for European and national parliaments.

But aside from France and the Netherlands, Eurosceptical Britain, Poland and the Czech Republic have failed to ratify the treaty and want it slimmed down or unpicked in ways that could upset the delicate balance on which it was built.

German Chancellor Angela Merkel, who has emerged as Europe’s most influential deal-maker, faces a tough challenge in trying to revive negotiations on reform at a summit in June. Yet the EU is far from paralysed, despite what Italian Economy Minister Tommaso Padoa-Schioppa calls a melancholy mood. Its leaders last week unanimously adopted an ambitious plan on climate change, energy efficiency and green fuels, claiming world leadership in the fight against global warming.

But unanimity rules have slowed moves to build a common foreign and security policy and tackle immigration and crime. Newcomers Cyprus and Poland have used their vetoes to block negotiations with Turkey and Russia, highlighting doubts about the ability of such a heterogeneous bloc to function.

On economic policy, countries such as France wad to by their own governments. If EU leaders can salvage key reforms in the constitution and either win or avoid another round of referendums, the Union may be able to overcome doubts over its future. If not, former Commission President Jacques Delors warned in a Reuters interview, it could unravel within 20 years.