VIENNA (Reuters) - Pressure mounted on Austria's far-right Freedom Party to fire one of its two top candidates for next month's EU parliament elections after he made racist comments and said the bloc made Nazi Germany's Third Reich look liberal by comparison.

Andreas Moelzer has apologised for saying the European Union was in danger of becoming a "conglomerate of negroes" who lacked the work ethic of the Germans and the Austrians.

And he has denied being the author of an article complaining that today's Viennese look like "raven-black" Austrian soccer star David Alaba and that one has to visit an old people's home to see what "real Austrians" used to be like.

The Freedom Party (FPO) is treading a fine line to position itself as a mainstream party electable by voters fed up with creeping EU centralisation who would not identify themselves as far-right.

The FPO is publicly standing behind Moelzer but in private FPO officials say the party leadership is unhappy with his behaviour and may take action.

Moelzer himself has rejected calls from all of Austria's other political parties and the leader of its Jewish community to resign, and faced down criticism from other European right-wing parties.

"That would hurt the party more than if I stayed," he told Austria's most popular tabloid Kronen-Zeitung in an interview published on Friday. "Of course it's a campaign against me because the FPO has very good chances in the EU elections."

He added that Alaba - whose parents are Nigerian and Filipina - was a "dear chap".

Harald Vilimsky, co-head with Moelzer of the FPO's EU election campaign, told Reuters that Moelzer's comments had been "unhelpful" but added: "Mistakes happen, and these have been acknowledged by Moelzer."

Moelzer's name has disappeared from schedules of events where he was due to speak in the next days.

Austrian FPO European parliament member Franz Obermayr, who is shepherding cooperation with other Eurosceptic, populist parties in his role as president of the European Alliance for Freedom, said Moelzer had been criticised by other members.

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Sweden Democrats EAF member Kent Ekeroth told Swedish newspaper Expressen in an interview published this week: "I think it is important to make clear that this sort of outrage cannot be tolerated."

And Obermayr, asked whether other EAF members had complained, told Reuters: "Of course there were also other negative voices," but declined to say whose they were.

Far-right, anti-establishment parties are expected to fare well in the European Parliament elections next month, mining voter dissatisfaction with high unemployment and entrenched centrist parties seen as out of touch, and fear of immigration.

The FPO is scoring around 27 percent in Austrian national opinion polls, ahead of the governing Social Democrats and conservative People's Party.

France's anti-immigrant National Front routed President Francois Hollande's ruling Socialists in local elections last week and eurosceptic parties are making gains in other EU countries on the back of weak economies.

(Reporting by Georgina Prodhan; Editing by Mark Heinrich)