In Indonesia, a shadowy campaign to stoke unrest as elections loom

* Political forces seen behind "black campaign"

* Attacks on mosques, clerics blamed on communists

* Reuters finds FPI spreading videos of hoax attacks

* Provincial polls in June ahead of 2019 national election

* Attacks mount in West Java, a key poll battleground

By Tom Allard, Agustinus Beo Da Costa and Kanupriya Kapoor

BANDUNG, Indonesia, March 23 (Reuters) - A spate of mysterious attacks on Islamic clerics, schools and mosques in Indonesia in recent weeks has ramped up tensions as the world's most populous Muslim-majority country heads into provincial elections and a presidential poll next year.

Intelligence and Islamic officials believe that political forces are behind what they describe as a shadowy "black campaign" designed to whip up fear that Islam itself is under siege under the leadership of President Joko Widodo.

In one town near the capital, Jakarta, a mosque manager was stabbed and a religious scholar received an anonymous letter warning that 10 clerics would be killed. Videos of what police say are fake attacks on Muslim clerics and schools have also been distributed on social media, heightening a mood of unease.

The attacks on the heavily populated island of Java have come as hardline Muslim groups press for a more conservative society and decry moderate politicians, posing a threat to Indonesia's reputation for tolerance and the democracy it won with the downfall of authoritarian President Suharto in 1998.

Indeed, there are echoes today of the panics stirred up by Suharto, which typically involved attacks on religious figures and institutions and sometimes a communist scare to discredit politicians.

Elections are due across the country in June for dozens of governors, district heads and mayors. Analysts see those polls as an opening skirmish before 2019's battle for the presidency.

Ridwan Kamil, mayor of the city of Bandung and frontrunner to become governor of West Java province, says he has been hounded for months by hoax stories online that questioned the strength of his Islamic faith.

"If you are not a Muslim, they will label you an infidel. If you are Muslim, they will label you not Islamic enough," Kamil said of his opponents in an interview with Reuters, declining to identify them.

"They're trying to send a message ... that the country is not safe, that the government is failing, that we need to replace the existing government. Who gets the benefit? Whoever challenges Jokowi," he said, referring to President Widodo, whom he supports for re-election, by his nickname.

A CAMPAIGN TO SOW DISCORD

The potency of religion as a swing factor in elections was graphically illustrated last year when the popular governor of Jakarta, Basuki Tjahaja Purnama, an ethnic-Chinese Christian and close ally of Widodo, lost his bid for re-election after being accused of insulting the Koran.