Germany and Italy have warned that a European Union summit next week may not agree a new EU constitution.
Speaking in Berlin, Italy's Prime Minister - and current EU president - Silvio Berlusconi said he was "55% optimistic" a deal would be reached.
His host, German Chancellor Gerhard Schroeder, said both men did not rule out failure in Brussels on Friday.
The biggest disagreement has been over voting powers among nations when the EU expands to take in 10 new members.
Germany and France, which together account for one-third of the bloc's population want the voting system to reflect their size.
But Spain and Poland fear domination by the bigger countries and have been fighting a fierce battle to hold on to a voting system agreed three years ago at the Nice summit.