By Paul Carsten

PATTAYA, Thailand (Reuters) - China is stonewalling attempts to start talks on a multilateral "code of conduct" governing the strategically located South China Sea and an agreement could still be years away, Southeast Asian officials said on Monday.

Beijing's assertion of sovereignty over the vast stretch of the water has set it directly against Vietnam and the Philippines, while Brunei, Taiwan and Malaysia also lay claim to other parts of the region, making it Asia's biggest potential military troublespot.

Speaking on the sidelines of a regional meeting in the Thai resort of Pattaya, Vietnamese Deputy Foreign Minister Pham Quang Vinh said there was no end in sight to the maritime dispute involving one of the world's main shipping routes and an area potentially rich in oil and gas.

"ASEAN thinks it is time to start talks to achieve a code of conduct as soon possible," said Pham, referring to the 10-nation Association of Southeast Asian Nations bloc, but added the grouping is meeting stoic resistance from China.

China has resisted proposals for a multilateral code of conduct for the South China Sea, preferring to try to negotiate disputes with each of the far less powerful individual claimants.

Sihasak Phuangketkeow, a Thai foreign ministry official, told reporters at the ASEAN-China meeting in Pattaya it might take another two years to agree a formal code of conduct.

Carl Thayer of Australia's University of New South Wales said China was unlikely to make any decision on the code of conduct until its once-a-decade leadership change is fully complete next year.

"I suspect because of changes in personnel likely to occur nobody in China is willing to commit themselves to something of this magnitude. There can be no compromise at the moment, coming from China. Leaders would be seen to be weak," said Thayer.

China has stepped up activity in the region, including establishing a military garrison on one of the disputed islands, and accused Washington of seeking to stir up trouble far from home.

The stakes have risen in the area as the U.S. military shifts its attention and resources back to Asia, emboldening its long-time ally the Philippines and former foe Vietnam to take a tougher stance against Beijing.

Unprecedented arguments over the sea prevented an ASEAN summit in July from issuing a joint communiqué, the first time this had happened in the bloc's 45-year history.

(Editing by Jeremy Laurence)