German Chancellor Angela Merkel will secure a parliamentary majority in favor of the planned permanent bailout fund for the euro zone, a senior coalition politician said on Saturday.

Some German media have reported increasing numbers of parliamentarians oppose the new, permanent European Stability Mechanism (ESM) taking effect in 2013 and there is disquiet over Greece's requirement for additional aid after last year's 110 billion euro package.

At the end, we will always have a clear majority, Rainer Bruederle, parliamentary floor leader of junior coalition partner the Free Democrats (FDP), told a party congress in the city of Rostock.

FDP dissenter Frank Schaeffler said 40 to 50 members of the coalition -- Merkel's Christian Democrats (CDU), its Bavarian sister party the Christian Social Union (CSU) and the FDP -- were considering voting against the ESM.

That would wipe out the coalition's majority in a parliamentary vote planned for the autumn, but Merkel can count on votes from euro enthusiasts among the opposition Social Democrats and Greens.

Coalition leaders also say Schaeffler is exaggerating, that eurosceptics are isolated and the government would have majority support, as Merkel predicted this week.

The FDP congress is due to vote on two euro zone motions, one for and one against the ESM, later on Saturday.

The pro-Europe motion called for strict parliamentary endorsement of every activation of the ESM and backed Merkel's insistence on private investors sharing the burden of sovereign default risks in the euro zone in future.

(Reporting by Andreas Rinke and Thorsten Severin; Writing by Sam Cage; Editing by Peter Graff)