WASHINGTON/BANDAR SERI BEGAWAN, Oct 26 (Reuters) - U.S. President Joe Biden will join Southeast Asian leaders for a virtual summit on Tuesday, the first time in four years that Washington will engage at the top level with a bloc seen as key to countering an increasingly assertive China.

The United States has not met with the Association of Southeast Asian Nations at the presidential level since Biden's predecessor, Donald Trump, attended an ASEAN-U.S. meeting in Manila in 2017. During that time, U.S. relations with China deteriorated, becoming their worst in decades.

A day after the ASEAN summit, Biden will participate in the broader East Asia Summit, which brings together ASEAN and other nations in the Indo-Pacific region, a senior U.S. administration official said.

"The President's participation in these summits demonstrates our commitment to the region and to a free-and-open Indo-Pacific and to supporting the security and prosperity of our partners," the U.S. official said.

Analysts say Biden's meeting with the 10-nation bloc reflects his administration's efforts to engage allies and partners in a collective effort to push back against China.

U.S. officials have, however, avoided specific mention of China in the run-up to the meetings as they work to set up a virtual summit between Biden and Chinese leader Xi Jinping later this year.

The White House said Biden will announce plans to provide up to $102 million to expand the U.S. strategic partnership with ASEAN, which is currently chaired by Brunei, with funding going towards health, climate, economic and education programs.

Biden is also expected to assure ASEAN that a recent U.S. focus on engagement with India, Japan and Australia in the so-called Quad grouping and a deal to supply Australia with nuclear-powered submarines are not intended to supplant ASEAN's central regional role.

Edgard Kagan, senior director for East Asia at the White House National Security Council, stressed last week that Washington does not see the Quad as "an Asian NATO" and that it was not intended to compete with ASEAN.

He said Washington had an interest in working with ASEAN to ensure supply-chain resilience, on climate, and to address "common challenges on maritime issues" - an apparent reference to China's broad claims in the disputed South China Sea.

While planning to provide a modest sum to promote trade with ASEAN, Biden has given no sign of any plan to return to a regional trade framework Trump withdrew from in 2017.

Analysts said ASEAN leaders would be anxious to hear how Washington plans to engage further on trade, investment and infrastructure and of any U.S. plans to step up provision of COVID-19 vaccines to the region, which has been hard hit by the pandemic.

An Asian diplomat, speaking on condition of anonymity, said the lack of an economic element in U.S. regional engagement was a major gap at a time when countries were expanding economic ties with China.

Kagan said it was critical for the credibility of the Quad that it deliver on a pledge it made in March to supply a billion COVID-19 vaccines to Southeast Asia by the end of 2022.

That plan stalled after India, the world's largest vaccine producer, banned exports in April amid a massive domestic COVID outbreak.

The ASEAN meetings will take place without Myanmar military leader Min Aung Hlaing, who overthrew a civilian government on Feb. 1 - a rare exclusion for a grouping usually known for non-interference.

Kagan called ASEAN's move to exclude the Myanmar leader a significant step but said more needed to be done to address the challenges that country is facing. (Reporting by David Brunnstrom; Editing by Simon Cameron-Moore)