By Alexandra Hudson and Ece Toksabay

ISTANBUL, Sept 11 (Reuters) - A clear majority of Turks willvote "yes" in a referendum on Sunday on constitutional reformsproposed by the government, pollsters said on Saturday in aboost for Prime Minister Tayyip Erdogan.

A survey by KONDA institute found the reforms, includingcontroversial changes to the judiciary, would garner 56.8percent support in the plebiscite, seen as an important gauge ofErdogan's support before a parliamentary election next year.

However, KONDA said 17.6 percent of the electorate remainedundecided. Polls earlier this week showed the vote was too closeto call, one predicting a narrow defeat for the package andanother suggesting it would pass by the flimsiest of margins.

Erdogan says the reforms will bring the constitution,drafted after a 1980 military coup, closer in line with those ofthe European Union, which Turkey seeks to join.

Among the 26 articles comprising the package are changes inthe way senior judges are selected. Opposition parties,including the CHP secularists, argue that these will enable thegovernment to exert more influence over the judiciary.

Defeat in the referendum would damage the ruling party'smorale before the parliamentary election, due by July 2011.

Tarhan Erdem, head of KONDA, said the AK party however didnot face a real challenge heading into next year's election, andvoting in the referendum would follow party loyalties.

"The lack of a strong party other than AKP is a majorshortcoming of Turkish politics.... falling opposition to thereforms is due to a decrease in support for the CHP," he said.

Kemal Kilicdaroglu took over the CHP in June after veteranleader Deniz Baykal resigned. While support surged to 35 percentfrom a previous 20 percent after his immediate appointment,Kilicdaroglu failed to keep up this momentum, Erdem said.

Party leaders were due to make final appeals on Saturday.

EXPAT VOTERS

Turkish citizens resident abroad have already been votingfor the last month at Turkey's borders and airports.

"I voted 'yes'. I think the referendum is important forboosting democracy and freedom. If Turkey wants to get into theEuropean Union it needs a strong democracy," said 36-year-oldMurat Sonmez, heading home to France from Istanbul airport.

Saniye Kosar, a 38-year-old housewife who lives in Belgium,said she was anxious about the strength of Erdogan's party.

"These changes are being made for the good of the AK Partynot for the good of society. I'm looking forward to voting 'no'.We may want to move back some day and I don't want to return toan Islamic state."

The AK regards itself as a Muslim version of Europe'sconservtive Christian Democratic parties, whereas criticssuspect that it harbours a hidden Islamist agenda.

Turkish markets are unlikely to move significantly if theconstitutional changes pass, but could turn bearish if thegovernment loses the plebiscite.

The KONDA poll was conducted on Sept. 4-5 and had a marginof error of plus or minus 2 percent.

In Brussels, EU foreign affairs chief Catherine Ashton triedon Saturday to build up support in the 27-nation bloc for closerpolicy cooperation with Turkey, despite divisions over whetherto grant accession to Ankara.

Ashton said EU governments ought to deepen ties with Turkeyto exploit its influential role as a negotiator in the MiddleEast and shore up Ankara's orientation towards the West.

"The purpose of today's debate is to recognise that as wellas an (EU) candidate, Turkey is a partner in foreign policychallenges," she told reporters during an EU foreign ministersmeeting.

Earlier this week, the British and Finnish foreign ministerspublished an opinion piece in the Financial Times backing herefforts to drum up support for Turkey because of its influentialrelations with Iran and Western Balkan states.

Divisions aside, EU governments want Turkey to conductfar-reaching democratic reforms, improve its human rights recordand end a row with Cyprus over a Turkish-controlled breakawaypart of the island before it can join the bloc. (Additional reporting by Omer Beberoglu in Istanbul andJustyna Pawlak in Brussels; Editing by Mark Heinrich)