German Chancellor Gerhard Schroeder has been rallying his party at the Social Democrats' convention, ahead of general elections next month.
Mr Schroeder wants a new mandate for controversial welfare reforms
Polls suggest the governing SPD is still trailing the opposition Christian Democrats, led by Angela Merkel.
Mr Schroeder said "nothing has been decided" and accused the opposition of promoting an uncaring society.
Correspondents say Mr Schroeder will need all his charisma to motivate the SPD for the last weeks of the race.
The chancellor is a seasoned campaigner known for his slick media skills and a more popular politician than Mrs Merkel, says the BBC's Ray Furlong in Berlin.
But these strengths have not translated into increased support for the SPD, which remains stuck at about 30%.
The 18 September election is taking place a year early, after the chancellor engineered the poll by deliberately losing a vote of confidence in July.
At the Berlin gathering, the SPD will adopt their election manifesto, which identifies unemployment as Germany's key problem.
Mr Schroeder told the convention that "Germany needed strong Social Democrats", in an address that won a standing ovation.
"Millions of women and men have yet to make their decision, and we should turn to them," he said.
Opposition leaders want "a completely different society... in which there is no longer place for solidarity and justice," he added.
"What they want is cold, it lacks in solidarity, and that makes it inhuman."
The chancellor also highlighted his "self-confident" foreign policy.
He pledged to defend German interests "without arrogance", but "when necessary, in the face of powerful friends".
At the CDU's convention at the weekend, Mrs Merkel told her party that they alone offered the country the chance of economic renewal.
She is set to face Chancellor Schroeder in a head-to-head television duel on Sunday.
Mr Schroeder announced in May that he would seek an early election, arguing that the SPD needed a fresh mandate for welfare and labour market reforms after suffering a series of state election defeats.