* Polls put Fillon in front for April-May election
* Hopes to win support of fellow conservative Merkel
* Fillon to discuss plans for Europe in Berlin
By Sophie Louet
BERLIN, Jan 23 (Reuters) - Former French prime minister Francois Fillon will seek some support from fellow conservative Angela Merkel in Berlin on Monday in the most unpredictable presidential election in decades.
Fillon, the only candidate in the April-May presidential election to be received by the German chancellor so far, will have lunch with Merkel before meeting her finance and defence ministers to discuss his plans for Europe.
Fillon is the frontrunner in opinion polls but his ratings have dropped slightly and surveys predict an increasingly tight race between him, far-right National Front leader Marine Le Pen and independent centrist Emmanuel Macron.
While Alain Juppe, a more centrist, staunchly pro-European Union candidate whom Fillon beat in the conservative primaries, was said to be Merkel's favourite candidate, the lunch meeting is a sign of support for Fillon.
But she looks unlikely to give him explicit backing - the lunch meeting is not open to the media and no joint statement is planned afterward.
Merkel, up for re-election herself in September, publicly backed conservative Nicolas Sarkozy when he sought re-election in 2012. He lost.
On the issue of economic reform, where Fillon proposes steep spending cuts, he is viewed by Merkel's government as an ally, but on other issues, from Russia and Turkey to migration and Europe, Fillon could prove a more difficult partner.
An aide to Fillon mentioned immigration and Russia as "two difficult topics," while insisting both agree on the need to take joint initiatives to boost the euro zone.
'PARTNERSHIP OF EQUALS'
"The Franco-German relationship is absolutely essential. Nothing in Europe will be done without its impetus," Fillon told Le Monde newspaper.
"I want to strengthen it, in a partnership of equals," Fillon said, accusing Socialist President Francois Hollande of weakening a partnership in which "the French and Germans do not speak frankly to each other."
In the interview with Le Monde, Fillon urged Europe to boost its defence capacity with a pooled fund to finance foreign operations. He renewed a call for the euro zone to shore up its institutions and sought to pre-empt fears he may let the French public budget deficit deteriorate.
While Fillon's comments about a "tightening" of the euro zone had raised some questions, his aide said he meant the single currency bloc's governance should be improved, not that it should have fewer members.