* Turkey holds municipal elections on Sunday
* Main opposition party lags Erdogan's AKP despite scandals
* CHP leader reforms secularist party to broaden appeal
By Ayla Jean Yackley
DENIZLI, Turkey, March 28 (Reuters) - Turkey's main opposition party has barely dented support for Prime Minister Tayyip Erdogan despite months of anti-government protests, an investigation into government graft and hours of incriminating conversations leaked online.
Kemal Kilicdaroglu, head of the Republican People's Party (CHP), at campaign rallies in more than 70 cities around Turkey, has emerged as Erdogan's most dogged public critic over the corruption scandal that has implicated the prime minister, his family and his closest ministers.
Yet Erdogan's Islamist-rooted AK Party remains comfortably ahead of the centre-left, staunchly secularist CHP in the countdown to Sunday's municipal elections.
"I am talking about efforts to legitimise corruption with an election," Kilicdaroglu said. "This is a test of our democracy."
But his message does not much resonate with religiously conservative Turks who remain broadly satisfied with AK Party rule after 12 years of solid economic growth. To them, the CHP looks like an exclusive bastion of Turkey's old secular elite.
"The CHP has failed to grasp politics is about addressing people's needs, not just concepts of identity like secularism," said Bekir Agirdir, director at political-research firm Konda.
"Rather than getting to understand the people better, it takes the same easy route that it has been treading for years."
A Konda poll showed AK Party candidates winning 46 percent of overall votes on Sunday, a dent in the 50 percent the party took in Turkey's last parliamentary election in 2011.
That compares with 27 percent for CHP, unchanged from 2011, and a combined 22 percent for parliament's other two groups, the Nationalist Movement Party and the pro-Kurdish Peace and Democracy Party, according to the survey of 3,067 people.
Other polls show a closer race in the key battlefields of Istanbul, where Erdogan was once mayor, and the capital Ankara.
The CHP's voter base has been largely confined to the secular-minded middle class. It has lacked broader appeal due to a patchy record on minority rights, support for an army that often meddled in politics and - at least until recently - strong opposition to religious symbols such as the Islamic headscarf.
The mild-mannered Kilicdaroglu, 65, has been quietly reforming the CHP, sidelining hardcore "Kemalists" who espouse a rigid version of the ideas of Mustafa Kemal Ataturk, founder of the modern secular republic, while promoting members seen as more closely aligned with European social democratic values.
"He has sought a balance between the new reformist wing and the traditional Kemalists to avoid splitting the party," said Sahin Alpay, a professor of political science at Bahcesehir University who once served as a senior adviser in the CHP.
Kilicdaroglu rejects the notion that the CHP is still the same party founded by Ataturk 90 years ago which ruled Turkey as a single-party state unchallenged for a quarter of a century.
The party flourished again in the 1970s, but other than short-lived stints as a junior partner in coalitions in the 1990s, it was largely banished until 2002, when it returned to parliament in the same election that swept AK to power.
Kilicdaroglu rose to prominence as the CHP's anti-graft campaigner, appearing on TV to brandish dossiers against officials which led to high-profile resignations.
He took the helm of the party in 2010 after Deniz Baykal, who controlled the CHP for 18 years, quit amid a sex scandal.
Under Kilicdaroglu, a new party charter has set quotas for women and youth. The CHP also dropped its staunch opposition to women wearing the headscarf in public offices and schools.
"We may have made mistakes in the past. But we're not afraid of facing our history ... We are the fastest-changing party in Turkey," he said in an interview this week, aboard a Cessna jet to a rally in the southwestern town of Denizli.
Change may not come fast enough for this election, but with the AK Party hurt by a slowing economy and the graft charges, Kilicdaroglu wants to position the CHP for a new landscape.
Nicknamed Gandhi for a passing resemblance to the father of Indian independence, Kilicdaroglu plays up his own humble background to counter the CHP's gilt-edged image. Born in a village in the eastern Kurdish province of Tunceli, he was the only one of seven children to attend university.
"My mother and my oldest sister could not read or write. I did not own an overcoat until I left for school. And yet I became chairman of the CHP. How is that elitist?" he says. "Our numbers are made up of farmers, labourers and tradesmen."
Erdogan, 60, dismisses Kilicdaroglu as an ineffectual rival, deriding the bespectacled former civil servant as a "manager".
He accused Kilicdaroglu of colluding with his political foes, including U.S.-based cleric Fethullah Gulen whose followers in Turkey held prominent positions in the police and judiciary and are believed to have launched the graft probe, including the wiretaps. Gulen has denied any involvement.
To warm up the crowd in Denizli, the CHP played the audio recordings leaked in the corruption scandal, which Erdogan has branded as an international plot to smear him.
"I believe the CHP will attract more religious voters because they recognise the greatest sin is ill-gotten gains," said Kilicdaroglu, whose party includes a former mufti for mayor of a conservative Istanbul borough among its candidates.
In Denizli, thousands gathered to listen to Kilicdaroglu describe a more inclusive CHP.
"Whether you cover your hair or you don't, all women have a place in my party," he said to loud cheers.
Retired factory worker Kiraz, who wears a simple scarf over her hair as a sign of her piety, wanted to hear what the CHP would do for the poor. She declined to give her last name.
"Covered or uncovered, I'm sure he'd take all the votes he can get," she said with a smile. (Editing by Nick Tattersall and Gareth Jones)