By Ranga Sirilal
COLOMBO (Reuters) - Sri Lanka's Mahinda Rajapaksa said on Thursday he would seek an unprecedented third term as president, prompting one of his lawmakers to join the opposition with a call to curb the presidency's "draconian powers".
Rajapaksa, 69, came to power in 2005 and won a second six-year term in 2010 on a wave of popularity after the military defeated Tamil Tiger separatists, ending a 26-year civil war.
His poll ratings have fallen sharply since, however, and critics, including his coalition partners, say Sri Lanka's "executive presidency" -- introduced by a 1978 constitution -- gives him and his family too much power.
"I am declaring a secret today. I have signed the proclamation calling for the election, for re-election for the third time ... That is democracy," Rajapaksa said, addressing a gathering shown on state television.
An Election Commission official said the poll would be held in early January.
Hours after the announcement, ruling party legislator Wasantha Senanayake defected to the main opposition party, saying he wanted to "change the draconian powers of the executive presidency and bring good governance".
"I believe that all (Sri Lankan) Presidents exercised dictator-like powers to a certain extent," he added.
Senanayake said other legislators might also quit Rajapaksa's United People's Freedom Alliance (UPFA) to try to unseat him, although a strong challenger has not yet emerged.
Hardline nationalist Buddhist party Jathika Hela Urumaya (JHU), which is in coalition with the UPFA, has also demanded that Rajapaksa cede some powers.
"We'll definitely defeat him if he doesn't abolish the executive presidency before the election," Athuraliye Rathana, a Buddhist monk and a JHU legislator warned last week.
Rajapaksa will be banking on Sinhala Buddhists, who account for around 70 percent of the population, to re-elect him. But his voter base could be split by a prominent Buddhist monk who also opposes the executive presidency.
Maduluwawe Sobitha, who heads the National Movement for Social Justice, has brought together most of the opposition parties to agree on a common candidate and demand the abolition of the executive presidency within six months after the polls.
Rajapaksa has said he will abolish the additional powers after the election, but made the same pledge in 2005 and 2010.
In moves seen as wooing voters, Rajapaksa announced many handouts and salary hikes in the 2015 budget, and has harped in speeches on the war victory under his leadership in May 2009.
But Rajapaksa's popularity is fading: his party won a recent provincial poll, but with 21 percent less support than in 2009.
Many accuse him of nepotism, corruption and politicisation of the judiciary and foreign services, charges he rejects.
Campaigning for the election is likely to coincide with a Jan. 13-15 visit to the island by Pope Francis, which Sri Lanka's Catholic Church has already asked all parties not to exploit for political advantage.
(Writing by Shihar Aneez; Editing by Catherine Evans)