* Turkey's Erdogan strengthens grip on power with local poll victory
* No significant progress on EU membership expected this year
* Turkey and EU bound by mutual interests despite tensions
By Luke Baker
BRUSSELS, March 31 (Reuters) - Sunday's resounding victory by the ruling AK Party in Turkey's local elections, undiminished by what some call an authoritarian turn by Prime Minister Tayyip Erdogan, is likely to put already cool relations between Ankara and Brussels in the chiller.
After months of revelations of high-level corruption and the furore caused by the government's blocking of Twitter and YouTube, Turkey finds itself at sharp odds with the European Union, which it has been negotiating to join since 1999.
Too much has been invested in the process to call talks off - trade, energy and infrastructure links make it as hard to break off as to push ahead. But the EU is very unlikely to nudge Ankara's accession hopes along until Erdogan shows he is prepared to protect civil liberties, justice and the rule of law - and govern like a mainstream European prime minister.
As if to underline that point, the European Commission delivered a terse statement within hours of final results showing AKP won 46 percent of the nationwide vote, a significantly higher tally than many expected.
"Following the overall worrying developments which have taken place over the past three months, Turkey ... now urgently needs to re-engage fully in reforms in line with European standards," a Commission spokeswoman said.
"It also needs to reach out to all citizens, including those which are not part of the majority vote, in order to build the strongest possible engagement on reforms needed to make progress on EU accession."
There is scant evidence Erdogan is listening, or feels he needs to. As leader of a country of nearly 75 million people which acts as an energy and trade hub and an anchor in an often unstable region, he sees Turkey as holding an upper hand.
His attitude to EU membership since coming to power has been summed up as "Europe needs Turkey more than we need them". That self-confidence will only have been reinforced by Sunday's results, which give him a powerful mandate.
"He'll be feeling 500 feet tall today, which makes him ruthless and able to do anything," said Amanda Paul, a Turkey expert at the European Policy Centre, a Brussels think-tank.
"It's a lot of power in the hands of a man who has become increasingly unpredictable and authoritarian," she said, suggesting it would have an impact on EU relations.
"We're going to go through quite a rough period now. It's safe to say that 2014 isn't going to deliver any serious steps forward when it comes to accession."
Part of the problem is that Brussels has next to no leverage over Ankara - and Turkey knows that very well.
While the EU could freeze negotiations launched in December on visa liberalisation, something Turkey had long yearned for, officials say that is not going to happen. Making travel visa-free would benefit the EU as well as Turkey, and to halt negotiations now is seen as an excessively tough sanction.
Instead, the approach is to remain as constructively engaged as possible, even if no progress on membership is made. In terms of geopolitics, regional security and NATO, of which Turkey is a core member, that is seen as the most rational attitude.
"We don't want to open a new front with Turkey, especially in the current geopolitical context with the Ukraine crisis," said a senior EU official involved with enlargement issues.
"Turkey has NATO's second largest army, it's a potential energy hub, and it is sensitively positioned close to Syria and Iran. The business community is also not at all tempted by a clash with Turkey."
Another consideration is Cyprus; Turkey is critical to efforts to keep the divided island's recently revived peace process on track. That in turn has implications for Europe's energy security, with Cyprus sitting on sizeable gas reserves.
Perhaps the clearest indication of Europe's ambivalence is how little criticism major capitals such as Berlin, Paris and London have expressed about Erdogan's internet clampdown.
While it can be debated who needs the other more, what is indisputable is that Turkey and Europe have far-reaching mutual interests that trump short-term political considerations.
European leaders may disapprove of Erdogan's actions, but he remains the prime minister they have to deal with, and there is a good chance he will secure a fourth term in elections in the spring of next year - giving him a hold on power until 2019.
Given that calculus, better to keep ties on ice while hoping for a change in attitude over time.
"International leaders will need to deal with the person who is running Turkey, all the more as he is confirmed as the strongman," said Sinan Ulgen, the chairman of Edam, a foreign policy think-tank.
"For better or worse, both sides will muddle along, and, yes, the EU will have zero influence on Turkey's domestic conduct." (Additional reporting by Paul Taylor; writing by Luke Baker; Editing by Will Waterman)