(Updates with quotes, details)
By Neil Chatterjee and Olivia Rondonuwu
JAKARTA, May 7 (Reuters) - Southeast Asian leaders sought on Saturday to resolve a deadly border dispute between Thailand and Cambodia that has cast fresh doubt over whether the region's plans to become a free-trade economic community by 2015 are realistic.
The skirmishes between Thailand and Cambodia -- ostensibly over ownership of some crumbling ancient temples on the border but also driven by internal political dynamics in both countries -- have killed 18 people in the last couple of weeks.
The confrontation -- and the apparent inability of the Association of South East Asian Nations to broker a lasting peace deal -- has fuelled scepticism over the bloc's lofty ambitions and threatens to overshadow its annual two-day meeting, just as controversy over Myanmar has in the past.
"We need to resolve the problem because we don't want this to be a problem that would affect ASEAN's agenda on community building," Thai Prime Minister Abhisit Vejjajiva told Reuters after meeting the group's leaders in Jakarta. "If the Cambodians would just come to the table, there is no problem."
Cambodia says it is the Thais who are blocking agreement, by repeatedly coming up with new demands to scupper peace.
The 10-member ASEAN, with some of the world's fastest growing economies and some 500 million people, represents a region with increasing economic clout, but has a policy of non-interference in other members' domestic affairs and is often derided as a talk shop.
"ASEAN must enhance its credibility by fully implementing its own agreements," Abhisit told leaders in a speech, referring to the group's charter. "To be credible, we must also be able to address and resolve challenges within our region."
Fighting over the 900-year-old Preah Vihear temple, a UNESCO World Heritage site in dispute since the withdrawal of the French from Cambodia in the 1950s, has turned into Southeast's Asia's bloodiest conflict in a decade and dented ASEAN's image.
Thai and Cambodian foreign ministers meeting ahead of the summit agreed on some of the ground rules for sending an Indonesian military observer team to the border, but Cambodia rejected Thailand's request to withdraw troops from the temple as a precondition.
Cambodia's foreign minister Hor Namhong said the country will never withdraw troops from its own territory.
MYRIAD SECURITY CHALLENGES
Indonesian President Susilo Bambang Yudhoyono avoided mentioning the dispute in a speech to open the meeting on Saturday, focusing instead on the region's challenges of food and energy security and speeding up moves towards an economic community.
The group ranges from oil and gas-rich Indonesia, Malaysia, Brunei, Vietnam and Malaysia, and the world's top rice exporter Thailand, to trading centre Singapore and resource-scarce Laos, Cambodia and the Philippines.
ASEAN, together with China, Japan and South Korea, has agreed to have a rice reserve of over 700,0000 tonnes to protect against volatile commodity prices, which had surged this year before unexpectedly diving this week.
The details of how the emergency reserve will work, such as whether countries will buy it or whether it could also be used to stabilise volatile prices, have yet to be thrashed out, Indonesia's Trade Minister Mari Pangestu said.
Indonesia surprised regional markets earlier this year by buying five times as much rice as expected, and vowed to lift its rice stockpiles by a third as it struggled to fight inflation after global food prices hit a record high.
"Food security will be a great challenge for ASEAN," Yudhoyono said in the speech. "Nations on this earth will face a competitive situation for the scarce resources of daily needs."
ASEAN needs to develop internal trade and investment, said Yudhoyono, a week after meeting Chinese Premier Wen Jiabao who offered $9 billion for infrastructure and to improve transport links with China. Transport disasters are all too common in Indonesia and at least 15 died in a plane crash on Saturday.
"We still have to do a lot of things," Yudhoyono added.
He said the leaders, transported in a fleet of gleaming Toyota limos through Jakarta's traffic jams and tropical rains that killed 17 people on Friday night in floods to the west of the capital, will also discuss disaster management following the devastating tsunami in key trading partner Japan.
Leaders may consider the wishes of Myanmar, a politically isolated state whose recent elections for civilian rule only gave it a veneer of democracy, to host ASEAN gatherings in 2014, as well as neighbouring East Timor's wish to join the group. (Additional reporting by Aditya Suharmoko, Telly Nathalia and Reuters TV; Editing by Andrew Marshall)