BERLIN, Sept 3 (Reuters) - Farm tractors are rumbling across Germany to a mass anti-nuclear rally in Berlin at the weekend which promises to thrust the divisive issue into the federal election campaign weeks before polling day.
The future of Germany's 17 nuclear power plants, due to be shut down by the early 2020s, is one of the major issues that divides Chancellor Angela Merkel's conservatives from the Social Democrats (SPD) of her challenger, Frank-Walter Steinmeier.
But it has been largely ignored in the run-up to the Sept. 27 election, in which Merkel's conservatives and their preferred coalition partners, the pro-business Free Democrats (FDP), are campaigning for an extension of nuclear power.
Thousands are expected to join Saturday's rally against those plans, led by farmers from Wendland -- a region through which nuclear waste is transported.
Political analysts said even though the long dispute between Merkel's conservatives and Steinmeier's SPD has had little impact on the campaign, the nuclear issue could mobilise voters in both camps -- particularly in the SPD.
"This demonstration has the potential to turn the nuclear issue into a hot topic down the home stretch," said Dietmar Herz, political scientist at Erfurt University, pointing to mass protests against past nuclear waste shipments to storage depots.
"So far it's played almost no role at all, which is a bit surprising considering it's one of the few issues where the CDU and SPD are completely at odds. I think we're going to see their differences on nuclear power highlighted in the last few weeks."
Data from the BDEW industry association shows that nuclear energy provided 23 percent of Germany's power needs in 2008, compared to 42 percent from coal-fired power stations, 14 percent from gas-fired generation and 15 percent from renewable energy sources.
"POST-NUCLEAR AGE"
Opinion polls show Germans oppose nuclear power, often by large majorities.
In 2001, the SPD pushed through legislation with their coalition partners the Greens to phase out the use of nuclear power in the world's third largest economy within two decades, despite protests from industry and utilities.
The CDU and their Bavarian sister party, the Christian Social Union, want to reverse the phase-out.
But they temporarily shelved those plans after a narrow election victory in 2005 forced them into a "grand coalition" with the SPD.
The SPD and Greens hoped Germany would lead the industrial world into a "post-nuclear age" but instead most of the country's trading partners have embraced the use of nuclear power as part of a climate-friendly energy mix. France, for example, gets 80 percent of its power from nuclear.
In their election manifestos, the SPD says it wants 50 percent of Germany's power to come from renewables by 2030 and the Greens are targeting 40 percent from renewables by 2020.
While the CDU and FDP also support renewables, they have less ambitious goals and say it would be irresponsible to phase out nuclear energy before it is clear that other sources can make up the deficit.
Rolf Martin Schmitz, a board member at German utility RWE, said independent studies showed keeping Germany's nuclear plants running for another 25 years would add hundreds of billions of euros to the economy.
"Ideological convictions aside, I can see a lot in favour of the idea, which would be in line with worldwide practice, he said at an energy event in Cologne on Thursday.
Nils Diederich, a political scientist at Berlin's Free University, expects the nuclear question to become a hot topic if Merkel's conservatives are able to form their centre-right coalition of choice with the FDP.
"If the CDU/CSU and FDP do actually win power and push through an extension of nuclear power we'll see a real battle," he said. "Then there will be massive demonstrations."