By Andrew Osborn and Anthony Deutsch
LONDON/AMSTERDAM, May 23 (Reuters) - Britain's Eurosceptic UK Independence Party made strong gains but their Dutch counterparts stumbled in elections to the European Parliament that are expected to produce a widespread anti-EU vote thanks in part to a low turnout.
Nigel Farage's UKIP, which wants to pull Britain out of the European Union and severely restrict immigration, grabbed seats from both the governing Conservatives and the opposition Labor Party in local elections held at the same time as the EU vote on Thursday, partial results showed.
If those scores are confirmed or amplified in the European ballot, from which results will only be released late on Sunday, it could increase pressure on Conservative Prime Minister David Cameron to take a harder line on reducing the EU's powers.
"Looking at the average vote shares across the country, and without wishing to count any chickens before they're hatched, it looks pretty good," an ebullient Farage said as evidence of his anti-establishment party's surge trickled in.
By contrast, far right Dutch populist Geert Wilders, whose anti-EU, anti-Islam Freedom Party had been forecast to top the poll in the Netherlands, was beaten into fourth place by pro-European parties in a surprise reverse, according to exit polls.
His PVV was projected to get just 12.2 percent, behind the centrist Democrats 66, the center-right Christian Democrats and Prime Minister Mark Rutte's right-wing liberals.
Wilders blamed the disappointing score on a low turnout of around 35 percent, saying that "by staying home (voters) showed their loathing for and disinterest in the European Union. The Netherlands has not become more pro-European."
Political analysts said the poor showing by the PVV may not be mirrored by UKIP or the National Front in France, but said it could still alter interpretations of the elections as a whole.
"The results will have a large effect on the media and political frame of the European elections, which was supposed to be 'far-right wins big' and will now look more critically at the actual results," said Cas Mudde, a political scientist at the University of Georgia in the United States.
Voters in Ireland and the Czech Republic began casting their ballots on Friday but most of the EU's 28 nations hold the election on Sunday. Some 388 million Europeans are eligible to vote for 751 members of the parliament, which is an equal co-legislator with member governments on most EU laws.
Opinion polls suggest anti-EU parties of the far right and hard left, which blame Brussels for austerity, recession and unemployment in the wake of the euro zone crisis, may win about 25 percent of seats, roughly double their current share.
But the parliament will remain dominated by pro-European center-right, center-left, liberal and Greens parties which often vote together in support of EU legislation.
Financial markets have so far been largely unconcerned by the prospect of a strong protest vote, partly because it has not prevented EU countries pursuing orthodox budget policies.
While the euro slipped against the dollar on Friday, interest rates on peripheral euro zone government bonds fell marginally, indicating little concern of political fallout.
In France, final polls put Marine Le Pen's far right National Front, which wants to leave the euro and restore national border controls and trade barriers, neck-and-neck with the conservative UMP party ahead of Sunday's vote, with President Francois Hollande's Socialists a distant third.
Other countries where Eurosceptics are expected to do well include Italy, where Beppe Grillo's anti-establishment 5-Star Movement is the main threat to Prime Minister Matteo Renzi's center-left Democratic Party, as well as Austria and Denmark.
In Greece, the score of Alex Tsipras' leftist anti-austerity Syriza party may determine whether conservative Prime Minister Antonis Samaras' coalition can cling to power and implement the rest of a deeply unpopular EU/IMF bailout program.
IMPACT ON BRITAIN'S CAMERON
In a possible first sign of UKIP's impact, sources familiar with Cameron's thinking said the British leader would lobby fellow EU leaders against nominating either of the two leading candidates of the mainstream EU parties as president of the executive European Commission.
Europe's main political families have agreed in principle that the candidate of whichever party tops the poll - either center-right Jean-Claude Juncker or Socialist Martin Schulz - should be the nominee to succeed Jose Manuel Barroso.
The EU treaty says the European Council of EU leaders must propose a candidate "taking into account" the parliamentary election and after appropriate consultations.
The British sources said Cameron, who has promised Britons an in/out referendum on EU membership in 2017 if he is re-elected next year, regarded both the veteran former Luxembourg prime minister and the German president of the outgoing European Parliament as too federalist.
"It's really important the next commission president is reform-minded. He (Cameron) will be talking to EU leaders about other candidates," one of the sources said.
Juncker and Schulz have both said EU leaders would be betraying the electorate if they pulled another candidate out of a hat in a backroom deal, although that is still very possible.
As so often in the EU, much will hinge on German Chancellor Angela Merkel, the bloc's most influential leader, who has backed Juncker in principle but also said it will take weeks of negotiation before a candidate emerges.
Merkel was due to take part in a joint election rally later on Friday with Juncker and David McAllister, the leading candidate of her Christian Democrats, on the market square at Saarlouis, a small town close to the French border.
German officials decline to discuss names but say they expect a package deal with several other EU jobs including the presidents of the European Council and the European Parliament, as well as the EU's foreign policy chief.
Although Britain has no veto over the Commission president, if neither main party has a big lead and turnout falls again despite efforts to personalize the election, seasoned Brussels diplomats say EU leaders are unlikely to force the matter to a vote and humiliate Cameron. (Additional reporting by Guy Faulconbridge and Kylie MacLellan in London, Thomas Escritt in Amsterdam and Michelle Martin in Berlin; Writing by Paul Taylor; editing by Ralph Boulton)