By Stephen Brown and Andreas Rinke
BERLIN (Reuters) - Angela Merkel is relishing the chance to debate the euro zone crisis with challenger Peer Steinbrueck in their only TV duel of the election campaign, despite a row over Greek aid that has put her government on the defensive, her campaign chief said.
Just over three weeks before the election, Steinbrueck's Social Democrats (SPD) have accused Merkel of hiding the true cost of the euro crisis from German voters.
Her predecessor Gerhard Schroeder has suggested she is lying about the prospects of another bailout for Greece, and Steinbrueck has promised to raise the subject in Sunday's debate.
But Hermann Groehe, who as secretary general of the Christian Democrats (CDU) is in charge of Merkel's campaign for a third term, said she would welcome an argument on Europe.
"We are glad to debate European politics because the high approval ratings that Angela Merkel enjoys among the German population arise not least from the confidence she has gained among the people through her successful work on the European debt crisis," he told Reuters.
"We have to defend the euro - from Red-Green softies who want to turn it into a 'debt union' and those who want a collapse of the euro zone or a return to the Deutsche mark."
He was referring to SPD proposals for shared euro zone debt liability and to calls by a new eurosceptic party, the Alternative for Germany, for a return to national currencies.
Polls suggest Merkel will win a third term but it is unclear whether she will be able to repeat her alliance with the pro-business Free Democrats (FDP) or will have to revive the "grand coalition" between her conservatives and the SPD of 2005-2009.
The debate over aid to Greece flared last week after Finance Minister Wolfgang Schaeuble broke a pre-election taboo and acknowledged that a third package was all but inevitable.
Until then, Merkel had refused to discuss the possibility, saying it was an issue that must be decided in 2014 or even 2015.
Groehe, a stocky 52-year-old who accompanies Merkel on her helicopter trips around Germany to campaign, said international pressure for action against Syria over a gas attack on civilians could also figure in the debate, but should not be politicized.
Like other German officials, he said the United Nations had to ensure the attack was investigated but was cautious about the prospect of Germany participating in any military action.
Polls show a majority of Germans oppose a military strike in Syria, but politicians also worry that Berlin could once again be marginalized if it does not support its allies. In 2011, Germany's reputation suffered when it sided with China and Russia in refusing to back a U.N. vote authorizing military intervention in Libya.
The SPD and the traditionally pacifist Greens have stressed the risk of armed action against Syria.
(Writing by Stephen Brown; Editing by Alison Williams)