By Dean Yates

PHUKET, Thailand (Reuters) - The United States will signal its renewed interest in Southeast Asia on Wednesday when Secretary of State Hillary Clinton signs a treaty that could assuage concerns in the region about China's growing influence.

Clinton, who arrives in the Thai resort of Phuket later on Wednesday, will also hold separate meetings with foreign ministers from regional countries to try to find ways to persuade North Korea to end its nuclear program.

Speaking in Bangkok on Tuesday, Clinton said she would sign the ASEAN Treaty on Amity and Cooperation when she meets foreign ministers from the Association of South East Asian Nations.

Other countries, including China, have acceded to the treaty, a document that underpins the 10-member grouping and which commits signatories to the peaceful settlement of disputes and non-interference in domestic affairs.

"I want to send a very clear message that the United States is back, that we are fully engaged and committed to our relationships in Southeast Asia," Clinton said.

Her talks on Wednesday come ahead of Asia's biggest annual security gathering, the ASEAN Regional Forum (ARF), which takes place on Thursday.

U.S. officials have said Clinton wanted to stress Washington's interest in ASEAN, a region home to 570 million people and with combined economic output of $1.1 trillion.

Washington routinely sent lower level officials to ASEAN meetings under former President George W. Bush.

"I understand they really, genuinely desire to expand and deepen cooperation and the relationship. We welcome that shift," ASEAN Secretary-General Surin Pitsuwan told Reuters.

Clinton is also likely to discuss Myanmar with ASEAN, whose soft approach to the military junta is a source of friction with the West. Even once it has signed the ASEAN treaty, Washington is unlikely to hold back condemning Myanmar's human rights record.

CHINA LOOMS LARGE

China's growing economic clout and huge market make it an important participant in ASEAN meetings, but tensions persist, especially over competing claims in the South China Sea, the shortest route between the Pacific and Indian Oceans.

Last year, trade between the United States and Southeast Asia was $178 billion, while cumulative American investment in the region is around $100 billion. China-ASEAN bilateral trade is worth $231.1 billion, with two-way investment around $60 billion.

Asked in Bangkok on Wednesday if Washington was trying to balance China's rise, Clinton said: "... The more we involve China in the work we are doing and in organizations like ASEAN, the more opportunities we have to create a positive framework."

"Now, I know that a lot of China's neighbors have expressed concerns, so we want to strengthen our relationships with a lot of the countries that are in East and Southeast Asia. But what we hope is that we all can work together and that China remains focused on raising the economic well-being of their people and competing in the market place."

The Washington-based Center for Strategic & International Studies (CSIS) in a report this month said Southeast Asia welcomed increased Chinese engagement but remained wary of the implications, particularly in military affairs.

"If there was a period in which the region succumbed to a Chinese 'charm offensive', that period is clearly over," said the report, based on extensive visits to the region late last year.

"While nations appreciated the benefits offered by China's rise ... regional interlocutors were often blunt about the challenges to national interests posed by China, in the South China Sea in particular, but also in the overall regional balance of power given China's military modernization."

(Additional reporting by Martin Petty, Ben Blanchard and Kittipong Soonprasert in Phuket and Arshad Mohammed in Bangkok; Editing by David Fox)