European Trade Commissioner Peter Mandelson has called for economic reform to make the European Union "relevant to its citizens".
Mr Mandelson was addressing a conference in Brussels
Mr Mandelson said the European Commission should fill the political vacuum caused by the French and Dutch rejections of the EU constitution.
The commission had to concentrate on economic growth and jobs, he said.
Speaking in Brussels, Mr Mandelson also said Britain might have to compromise "for the common European good".
He accused some of the bigger countries in core Europe of having an emotional block about economic reform.
Addressing a Brussels conference of the European Policy Centre and the University Association for Contemporary University Studies (UACES), he said the commission's leadership had been eroded.
Mr Mandelson said it had "to put itself into the driving seat, providing more of the leadership that our member states and public crave".
"I am not advocating a bout of regulatory hyperactivity on the Commission's part. What we need is focus and impact," he said.
With Britain currently holding the presidency of the European Union, Mr Mandelson said Tony Blair had a real opportunity for leadership as well. But he warned there were four conditions Britain would need to meet:
"First, as the government has begun to do, if Britain does not always claim a monopoly of virtue - that the Brits have got everything right and the Continentals everything wrong.
"Second, if Britain argues for reform from a pro European perspective - not to cut back and limit Europe in order to return powers to the nation state.
"Third, if Britain does not exaggerate its case, for example on the CAP where the real issue is the pace and direction of reform, not whether the CAP should be scrapped, as Margaret Beckett has made clear.
"Fourth, if Britain shows a willingness to compromise for the common European good on the argument that it is more in Britain's interest that Europe moves forward than she wins on every last point."
Mr Mandelson said the commission was the only organisation that could persuade member states to live up to their responsibilities.
"Europe has been on the defensive for too long. Let us go on the attack.
"With Blair in the presidency and Barroso at the commission we can start the battle to make the idea of Europe live again."