BANJUL, Nov 22 - Gambian President Yahya Jammeh is poised to win a fourth term in elections this week in the West African country, popular with tourists for its tropical beaches but notorious for its human rights abuses and muzzled press.

Jammeh, who once claimed to have a herbal cure for AIDS and who believes in witchcraft, will face two challengers in the November 24 vote, in which Gambians will drop marbles into drums, instead of marking ballots, a survival from colonial days.

The former soldier's re-election to a new five-year term looks almost certain after 17 years of rule that began with a 1994 coup and has since been marked by lethal crackdowns on protests, mass arrests of opponents, and military reshuffles.

The streets of the capital Banjul were adorned with pro-Jammeh posters, and residents sported pro-Jammeh T-shirts on Tuesday, the last day of 11 days of campaigning. There was little sign of opposition campaigning.

Given sustained intimidation of critics, few voters have any faith in elections as a viable means of effecting change, said Jolyon Ford of Oxford Analytica. Eventual military coup remains a more likely Jammeh exit scenario than electoral defeat.

The United States sees the Gambian government as an important ally in the war on terror and West African drugs trafficking, and some Gambians credit Jammeh with improvements in infrastructure, education and healthcare.

But international human rights watchdogs have repeatedly slammed Jammeh for stifling dissent and press freedoms, and regional neighbours including Senegal and Guinea have accused him of trying to destabilize them.

Jammeh, 46, will face off against opposition veteran Hamat Bah, 51, - representing a four-party alliance - and Canadian-trained attorney Ousainou Darboe, 63.

MARBLES, NOT BALLOTS

The opposition has complained that 11 days is too little for campaigning and that Jammeh's tight control of the judicial system makes beating him almost impossible.

Jammeh has won all three elections since his coup, including his best result in 2006 with more than 67 percent of the votes cast, though the wins have been tainted by accusations of fraud.

Nearly 800,000 Gambians have registered to vote in Thursday's elections, up from 670,000 in 2006.

Gambia, a slither of land along the Gambia River, sandwiched between northern and southern Senegal, retains an archaic method of voting devised by British colonists.

Voters are given one marble each, which they drop into a drum corresponding to the candidate of their choice. The marble strikes a bell inside the drum, preventing multiple voting.

Jammeh's re-election would likely keep the country on its sound economic trajectory - growth of 5.5 percent or more is expected in 2011 and 2012 on the back of good harvests and increases in tourism - but would disappoint rights activists.

The rule of law, press freedom and the right to air views is essential in a democratic state, which is presently lacking under Jammeh's government, said rights activist Moussa Faal.

Black marks on Jammeh's record include security forces' crackdown on a protest in 2000 that killed at least 11, the jailing in 2010 of an opposition figure for using a microphone without permission, and the censorship of local media.

The poor record is likely to worsen, with unlawful arrests of opponents and journalists, said Lydie Boka, head of risk consultancy StrategiCo.

Jammeh says he has thwarted several coup attempts, and has jailed officers and carried out repeated military reshuffles - which Boka said may increase the chance the military eventually removes him.

Some 13 containers of Iranian weapons headed to Gambia were seized in a Nigerian port last year, leading Senegal to recall its ambassador from Tehran. The purpose of the shipments was unclear, but Senegal's southern Casamance region has been the scene of a separatist rebellion since 1982.

Guinea's president also said in September that Gambia was aware of a plot to kill him in July.

(Writing and additional reporting by Richard Valdmanis; Editing by David Lewis and Tim Pearce)

(This story was corrected in paragraph 16 to change the date of the jailing of opposition figure)