(Add details) By Achmad Sukarsono BANDA ACEH, Indonesia, Dec 11 (Reuters) - A former rebel in Indonesia's Aceh province, who had to scramble out of a flooded jail cell two years ago to escape the Indian Ocean tsunami, believes he can win the governorship outright in a landmark poll. Monday's election is the first ever direct vote for top executive posts in the province and is seen as a key step towards consolidating a peace deal struck in August 2005 between Jakarta and the separatist Free Aceh Movement (GAM). So far it has succeeded in ending the fighting that killed 15,000 people after GAM launched a struggle in 1976 for an independent state in Aceh, at the northern tip of Sumatra island. "I am confident that we could win this election in only one round. You will see," Irwandi Yusuf, a veterinarian who negotiated for GAM in talks with Jakarta, told Reuters in an interview late on Sunday at GAM's office in the provincial capital Banda Aceh. Irwandi was among dozens of rebel prisoners and other inmates who had to climb onto the roof after huge tsunami waves slammed into the prison in Banda Aceh. More of an academic than a gun-toting rebel, he was arrested in Jakarta in 2003 and sentenced to nine years in prison for his work as an underground campaigner and spin doctor for GAM. In addition to being a lecturer at Aceh's state-run Syiah Kuala Universty, at his trial he was shown to be responsible for GAM's media releases and to have served as a speechwriter for several exiled rebel leaders. Many analysts feel the race for governor involving eight candidates will be extremely tight and say it is unlikely any individual candidate will grab 25 percent of the vote, the minimum required to win the job outright. That means a run-off between the top two vote-getters is expected. The prospect of a clear winner has also been clouded by a split in GAM's vote base between Irwandi and a social activist who has paired up with a GAM old guard who wants to be deputy governor on a ticket backed by Indonesia's leading Islamic party. "We are split on the elite level but not at the lower level who know who I am and what they really want," Irwandi said. If none of the GAM-linked candidates get the governorship, Irwandi said that could invite suspicion of Jakarta meddling. The bespectacled 46 year-old also dismissed as "impossible" suggestions that a loss for GAM due to the split could spawn multiple parties when they are allowed to form in the spring. FIGHTING CORRUPTION Irwandi said if elected he would first clean up local bureaucracy and eliminate corruption that has plagued development in tsunami-devastated Aceh. "This is the locomotive. If it does not change, others will not move. If we cannot eliminate corruption, how can we gain trust from the people," he said. Irwandi eventually became the rebel representative to an international mission monitoring the 2005 peace pact. The pact came about after months of negotiations, partially spurred by the Dec. 26, 2004 Indian Ocean tsunami that left around 170,000 Acehnese dead or missing and 500,000 more homeless. "There was no need anymore to call for independence when Aceh had been depopulated. We were willing to sacrifice our feelings and objectives," he said, referring to the impact of the tsunami. Asked about the implementation of elements of Islamic sharia law in the province, he said there were burdens attached to the move. In 2001, staunchly Muslim Aceh became the only province in Indonesia allowed to independently insert sharia into local laws. "But I cannot say no to it because that will clash with our grassroots. However enforcement needs finessing so that it would not be over reactive," he said. Experts say most in Aceh accept the sharia arrangement but some have complained about intrusive enforcement. "Sharia is there to educate people, improve their welfare, not for spying," Irwandi said.