Forging a common front and encouraging bolder rhetoric against Chinese assertiveness in the South China Sea, however, will be a challenge among the diverse collection of VIP guests, who did not criticise China by name in past joint summit statements as the disputes flared on and off in recent years.
Decisions by the Association of Southeast Asian Nations, the bloc they lead, can easily be stalled.
ASEAN includes governments aligned either with Washington or Beijing. Only four of its 10 member states are locked in the disputes with China and Taiwan, leading to sometimes conflicting views on handling the long-simmering rifts.
In recent years, summit statements have expressed concern over the escalating conflicts and called for freedom of navigation and overflight in the disputed territories, but they have rarely gone to specifics.
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"I think it will be hard for the US to convince the 10 ASEAN states to adopt any language on the South China Sea disputes that go beyond what ASEAN statements have said in the past," said Dr. Malcolm Cook of the Institute of Southeast Asian Studies in Singapore.
With Obama in his last year in office, certain ASEAN member states would probably not concede on any security or economic issue that might antagonize China, an economic lifeline to them, Cook said.
There have been initial differences among the governments on the wordings of the statement, said the diplomat, who spoke on condition of anonymity because of a lack of authority to discuss details of the negotiations with reporters.
Vietnam and the Philippines, whose disputes with China have intensified in recent years, prefer a more detailed reference to the territorial disputes, including mention of international arbitration as an option to resolve the conflicts.
In 2012, Cambodia refused to mention discussions in an ASEAN foreign ministerial summit statement about a shoal disputed by China and the Philippines.
An ensuing argument caused the summit to end without a joint statement for the first time since the bloc was founded in 1967.
While the statement can be restrained, the diplomat said any leader can speak freely at the informal talks in Sunnylands.