The country's politicians have been on the hustings for months, but the campaign for Germany's Sept 24 general election formally kicks off only this weekend.

That is when German political parties can legally start spending federal money on public rallies and other electoral activities.

If opinion polls are to be believed, the electoral outcome is not in doubt. Already in power for 12 years, Chancellor Angela Merkel seems set to win her fourth term next month. But the make-up of the coalition which Dr Merkel will lead remains far from clear. And so are the policies of Germany's main parties, which are only now being presented to the electorate.

Given its turbulent history, Germany's electoral system is specifically designed to make it impossible for a single party to rule alone. Governments are coalitions between either Dr Merkel's centre-right Christian Democratic Union (CDU) or the centre-left Socialists - SPD, as they are known by their German acronym - and one of the country's smaller parties.

But for most of Dr Merkel's time in power, she has presided over so-called "grand coalitions", in which both the SPD and CDU ruled together as no other parliamentary combination proved workable. As a result, the two big parties are now planning to spend their first weeks of campaigning by re-emphasising their differences in order to reconnect to their core voter base.

This task is easier for the Christian Democrats, who benefit from the country's current economic prosperity, as all that Dr Merkel, their leader, has to do is to promise more of the same.

"For a Germany in which we live well and happily", declare the CDU's electoral posters, against a background photo of a smiling Dr Merkel, 63.

This message seems to resonate even with young first-time

voters, who usually support left-wing causes - opinion polls suggest that 57 per cent of voters in the 18 to 21 age bracket will opt for Dr Merkel. Overall, 40 per cent of voters support the CDU, according to the latest surveys.

The Socialists face a much tougher challenge as they do not have an appealing leader and have to tread a careful line between attracting left-wing voters with promises of more welfare programmes without alienating a middle-class and ageing electorate weary of higher taxes and economic experiments.

The SPD's decision to pick Mr Martin Schulz, a former president of the European Parliament, as their candidate for chancellor initially looked as one way around the problem.

Mr Schulz, who spent many years outside Germany's domestic politics, came across as both a fresh face and as reassuringly moderate.

But talk of a "Schulz bounce" in opinion polls came to nothing: The SPD is now trailing badly and may get not more than 23 per cent of the ballots, one of the worst results ever for a party which has dominated Germany's political life since the 19th century.

Desperate for a policy to attract voters, the SPD has now hit upon a novel initiative: fierce opposition to Germany's plans to spend 2 per cent of its gross domestic product (GDP) on the military, as Dr Merkel is pledged to do under Europe's alliance arrangements. Germany now spends only 1.3 per cent of GDP on its armed forces.

Mr Schulz has rejected the 2 per cent target as "completely unnecessary and unrealistic", claiming that it was imposed on Germany by United States President Donald Trump, who is hugely unpopular with ordinary Germans. That is untrue - the German government has promised larger defence budgets for years. Still, the pledge to freeze money for the military and "spend it on education instead", as SPD officials now say, may appeal to poorer workers in industrial cities, who are increasingly marginalised by a lack of skills and education.

Yet, it is doubtful that this initiative alone could save the SPD from a severe mauling on Sept 24, partly because defence is not a key electoral issue in Germany, but also because Dr Merkel has promised to increase military spending only gradually, so she can easily dismiss the current debate as artificial.

Dr Merkel's chief problem is not, therefore, her party's performance, but that of the small centrist Liberals, who are her preferred coalition partners for the next government and her only hope of avoiding partnering again with the SPD.

Initial opinion polls indicated that the Liberals may get up to 10 per cent of the ballots, more than enough to provide Dr Merkel with the majority she needs to form a government. But latest indications are that the Liberals are sliding back in popularity, and each percentage point can make a huge difference.

So, although the ultimate winner in Germany's elections is not in doubt, the shape of its government will be determined by what still promises to be a tough and closely fought campaign.