German Chancellor Angela Merkel aims to rally leaders behind plans to diversify the bloc's energy sources when she steps on to the centre stage of European politics as chair of the two-day summit -- the first under Germany's EU presidency.

Merkel, a former environment minister, said on the eve of the gathering that the European Union was in a position to mark out an ambitious path for other nations to follow in confronting the threat of global warming.

"Europe cannot enter this battle alone. It's a global struggle and we all need to contribute," she told journalists. "I think the more we are able to set a good example, the more we can convince others."

EU leaders are expected to endorse plans to cut carbon dioxide (CO2) emissions by 20 percent by 2020, from 1990 levels, and by 30 percent if other developed and emerging economies, particularly China and India, join them.

Before the summit started, officials reported broad agreement on the main targets, but sharp differences over how nations will share the burden of the cuts and on commitments to embracing renewable energy sources.

"That will be a difficult discussion," a British official acknowledged.

Some newer EU members like the Czech Republic, Hungary and Poland with a heavy dependency on carbon-heavy energy fuels like coal, are opposed to plans to set a binding target for renewable energy sources to make up a minimum 10 percent of the EU's overall make-up by 2020.

Green members of the European Parliament are up in arms that France, which meets 40 percent of its energy needs with atomic sources, is lobbying for nuclear energy to be considered a renewable source.

"Agreeing a binding target for renewable energy in the EU is the bare minimum of what needs to be done," said British Green MEP Caroline Lucas.

"EU leaders must not allow this week's summit to be blackmailed by the nuclear industry, through its outgoing proxy (French President Jacques) Chirac," she added.

The veteran French leader will be in the spotlight as the summit almost certainly marks a last chance to leave his imprint on EU policy-making.

In addition to marking Chirac's swansong, the summit comes amid a shifting European political landscape.

British Prime Minister Tony Blair, who has often clashed with Chirac on issues as diverse as farm subsidies, the Iraq war and the EU budget, is increasingly seen as a lame duck given his stated plans to leave office in the near future.

Italian Prime Minister Romano Prodi, a former European Commission chief, has emerged shaken from a recent political crisis which forced a vote of confidence in his premiership.

French presidential elections in April and May will usher in a new generation, while a number of smaller countries such as Austria and Sweden have young governments, adding further uncertainty to the EU's political course.

Poland is increasingly playing the bad boy on the European stage by clashing with its EU partners on subjects ranging from its public finances to protecting environmentally sensitive areas.

Merkel, meanwhile, has a chance to seal her reputation as the rising star of European politics after earning respect in late 2005 when she brokered a deal on the bloc's long-term budget.

She will present her fellow European leaders with ideas for a key 50th anniversary declaration on the EU's achievements and goals, but getting all 27 member states to tick the same boxes on what makes the EU great will be no mean feat.

There will be no quibbles over the fact that Europe's major players have avoided going to war with each other since the EU's founding Treaty of Rome was signed on March 25, 1957.

That aside, there is a distinct lack of consensus on the achievements and goals that should be highlighted, with some envisioning a lean, mean cross-border free market, and others a broad social system and the beginnings of a superstate.

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