By Daniel Flynn and Katrina Manson

FREETOWN, Aug 11 (Reuters) - Sierra Leoneans vote on Saturday in their first presidential election since U.N. peacekeepers left two years ago, a test of the West African state's recovery from a 1991-2002 civil war.

Ernest Bai Koroma of the opposition All People's Congress (APC) is expected to mount a strong challenge to Solomon Berewa, the country's vice president and candidate for the ruling Sierra Leone People's Party (SLPP).

President Ahmad Tejan Kabbah, re-elected on a wave of post-war euphoria in 2002, is stepping down as required by the constitution amid anger at rampant corruption and the SLPP's failure to supply jobs, electricity or roads in one of the world's poorest states.

Berewa has vowed to curb graft if he wins.

A parliamentary election is also taking place and some 2.6 million Sierra Leoneans, roughly half the population, are registered to elect 112 parliamentarians.

Campaigning has been largely peaceful and electoral officials have appealed to Sierra Leoneans to avoid violence. Memories of the war, which killed 50,000 people, have overshadowed the polls.

"This is an activity that is going to make or break us as a nation," said the head of the National Electoral Council, Christiana Thorpe.

"Please let us give ourselves another chance."

After two days of downpours, officials were concerned the rainy season could disrupt voting, particularly in the rural east. Ballots have been transported by army trucks, canoes and even porters to some 6,176 polling stations in the savannahs, jungles and mountains of the interior.

Polls open at 7 a.m. (0700 GMT) and were due to close at 5 p.m. If no presidential candidate wins more than 55 percent of the vote, the election will go to a runoff, probably in early September.

Sierra Leone's war was infamous for images of child soldiers who hacked limbs off civilians and now young Sierra Leoneans have the chance to decide the fate of their country. More than half of voters are under 35.

"That's the good thing about democracy: you try one party and if they fail, you kick them out," said Saliou Diallo, 32, a waiter in Freetown.

In Sembehun Ngaula, a rice-farming village some 185 miles (300 km) southeast of the capital, heavy rains washed out the bridge into town. Most of the 550 of so voters here will have to struggle many miles through the mud to cast their ballot.

The region was hit hard during the war. Many buildings and homes were destroyed and have yet to be rebuilt. Many of their occupants fled.

"I don't want to run any more. I was on the run for 10 years," Lamin Lappia, a farmer from Sembehun, said. "If we use violence we will suffer. The politicians will not suffer." (Additional reporting by Naomi Schwarz)

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