Barroso, when asked about Angela Merkel's aim to save the constitution rejected by French and Dutch voters in 2005, said: "I want to give you an honest answer: the EU constitution in its current form will not come into effect.
"We should not fool ourselves. It's important now to maintain its values, its principles and its substance. Above all, we have to improve the decision-making mechanism, and we need to do that as quickly as possible."
Barroso said: "I have confidence the Germany presidency can take important steps in this direction."
Germany takes over the EU presidency for six months with an agenda of reviving institutional reforms. The EU is set to grow to 27 members when Bulgaria and Romania join on January 1.
German leaders said they hoped to map out a timetable and blueprint for the EU constitution by the end of its presidency. Frank-Walter Steinmeier, the German foreign minister, has pointed out that two-thirds of the EU members are behind the constitution.
At their last summit in Brussels earlier in December, EU leaders remained divided on whether and how to revive the stalled EU constitution, a treaty stalemate expected to last well into 2008.