* No breakthrough in Thai-Cambodian border row
* Credibility of ASEAN at stake
* Foreign ministers to extend stay in Jakarta to discuss (Adds quotes from Indonesian president)
By Olivia Rondonuwu and Aditya Suharmoko
JAKARTA, May 8 (Reuters) - Southeast Asian leaders failed to achieve any breakthrough on Sunday to end deadly border skirmishes between Thailand and Cambodia that overshadowed a regional summit in Jakarta supposed to showcase progress towards economic integration.
The clashes around crumbling Hindu temples in disputed areas have starkly illustrated the tensions between countries in the Association of South East Asian Nations (ASEAN) that could derail plans to create a single economic community by 2015, and the apparent inability of the bloc to deal with disagreements.
Indonesia, host of the 18th ASEAN summit, has been pressing for a deal that would prevent the meeting being marred by the border dispute. But in the end all that was achieved was a face-saving announcement that the Thai and Cambodian foreign ministers would stay an extra day in Jakarta for more talks.
The two sides have spoken plenty of times in recent weeks, but without finding a resolution to clashes that have killed 18 people since April.
ASEAN, a collection of authoritarian states and nascent democracies, has a policy of non-interference in each other's domestic affairs, and so has struggled to resolve the border dispute which -- although on the surface about ownership of some ancient temples -- is being driven by domestic political dynamics in both Thailand and Cambodia.
THAI ELECTIONS COMPLICATE DISPUTE
Thai Prime Minister Abhisit Vejjajiva told Reuters on the sidelines of the summit he will go to the polls on July 3. With elections approaching, the border issue is one which he can try to use to unite Thais behind him. He will certainly not be looking to make any concessions that would lose him votes.
The party seen as the biggest rival of Abhisit's Democrats is Peua Thai, a political vehicle for exiled former Prime Minister Thaksin Shinawatra who has close ties with Hun Sen and was briefly even an official adviser to him.
Abhisit insisted that Thailand wanted peace and was not looking to score political points.
"The ultimate objective must be to achieve lasting peace, so that both our peoples can live peacefully side-by-side along the Thai-Cambodian border," he said in a press briefing.
But he laid the blame for the border tensions squarely on Cambodia, fuelling scepticism over whether the extra day of talks on Monday will achieve anything.
Yudhoyono repeatedly called for ASEAN unity during the summit, but intense efforts by Jakarta, including proposals to send Indonesian military observers to disputed areas, did not bridge the gap between Thailand and Cambodia.
"ASEAN leaders wish both countries to choose a peaceful solution, prevent the conflict escalating, and redouble efforts to avoid fighting between the two armies," Yudhoyono said at the summit's closing news conference.
"Indonesia, as the ASEAN chair, has made many efforts to resolve the situation by suggesting ways of achieving a peaceful resolution."
Other ASEAN nations were not happy with the tension.
"They need to ponder how badly the ill will generated would impede ASEAN collaboration on projects... An ASEAN disunited will be taken less seriously by investors," said Singapore's state-controlled Straits Times newspaper in an editorial.
SECURITY CHALLENGES
Singapore leader Lee Hsien Loong did not attend the summit, staying at home for general elections that saw the ruling People's Action Party easily returned to power as expected. But the foreign minister lost his seat in a landmark vote for an opposition bolstered by a more sceptical younger generation.
The rest of the region's leaders, meeting in a cavernous conference centre with an intricately carved wooden ceiling, have also struggled to engage the region's 500 million people in a project to build an economic community with free movement of people and goods by 2015.
"If the Cambodia and Thailand situation gets worse, then I'm afraid they might have to postpone it to 2020 or even put it on hold," said Enrico Tanuwidjaja, an analyst at OSK-DMG Group in Singapore.
In a venue patrolled by hundreds of police and military personnel after worries over reprisal attacks by Islamists in Indonesia following the killing of Osama bin Laden, leaders were discussing security challenges such as food and energy supply.
The group ranges from oil and gas-rich Indonesia, Malaysia, Brunei, Vietnam and Malaysia, and the world's top rice exporter Thailand, to port trading centre Singapore, resource-scarce Cambodia and the Philippines, and impoverished Myanmar and Laos.
The fast-growing region has again become a magnet for emerging market investors and is trying to develop its $1.8 trillion economy by negotiating bilateral trade deals with the European Union and improving transport links with key trading partner China.
Previous meetings have often been overshadowed by controversy over member Myanmar. The country has asked to chair ASEAN in 2014, a request which, if granted, would greatly complicate ties between the bloc and the United States and European Union.
A draft communique from the summit said the request had been agreed, but leaders later backpedalled. The final statement issued from the meeting said only that the request was being considered, although Yudhoyono said there would be no objection if Myanmar continued making progress towards democracy. (Writing by Neil Chatterjee; Editing by Andrew Marshall)