By Surapan Boonthanom YALA, Thailand, Aug 18 (Reuters) - Police and troops in Thailand's rebellious Muslim south have beefed-up security ahead of Sunday's constitutional referendum, fearing rebels will sabotage the polls in retaliation for the arrests of dozens of Muslim suspects.

The number of police guarding polling stations has been increased and security forces have been reassigned to escort election officials in Pattani, Yala and Narathiwat provinces, where more than 2,500 people have been killed in near-daily violence since 2004.

"They may be planning attacks on Muslim voters on the referendum day and blaming them on the government forces," Army spokesman Atthadej Mathanom said.

A southern police general said 16,000 officers would be deployed on Sunday to keep peace in the predominantly Malay-speaking region, but Attadej declined to disclose the number of troops.

In recent weeks, security forces have launched raids almost daily on suspected insurgent hideouts in villages and towns.

At one point, close to 400 people were held without charge, although the army said around half of those had since been released.

Despite the threat of violence, Election Commission officials expected voter turnout in the far south to reach 60 percent, higher than in the capital, but lower than in some other regions.

But local politicians said the figure was too optimistic as many Muslims, who account for 80 percent of the local population, could not speak or read Thai and could not understand the 200-page charter, copies of which have been handed out to every household.

Despite attempts by election officials to get Muslim clerics to translate highlights of the charter into the Malay dialect, many people believed it will have little impact on their lives.

"How can they believe that this new charter will better protect their rights and liberty while the region is still under martial law," said Somboon Ahmad Bualuang, mayor of Puyud sub-district in Pattani province.

The charter is designed to prevent the re-emergence of a strong, single-party government like that of Thaksin Shinawatra, who was ousted a prime minister in a bloodless coup last year.

Analysts say the new charter would mean a return to the constantly collapsing coalitions of the early 1990s.

But that message may not be effectively communicated to voters in the Muslim south.

"I don't know anything about the constitution. All I know is how to make ends meet," said Aesoh Puteh, 30, who sells roasted chicken in a market in Yala.

"I thought referendum was for those in Bangkok only."

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