President Barack Obama hosts South East Asian leaders at a California desert retreat Monday, hoping to increase pressure on China over land grabs in the South China Sea.

Obama hosts representatives from 10 ASEAN countries at Sunnylands, a secluded 200 acre resort beloved by US presidents since Dwight Eisenhower.

The White House sees this summit, and the prestigious venue, as an opportunity to champion Obama's "pivot to Asia" and ASEAN's growing importance, before the president leaves the White House in January 2017.

But the more immediate aim will be to secure a united front against China's island-building and military build-up in areas that are subject to a myriad of territorial claims.

The White House, betting that China does not want to be seen as a regional bully, has mustered an informal coalition of Pacific allies to demand that Beijing respect the rule of law.

That effort will deepen at Sunnylands, where leaders are expected to discuss a common response to a key UN court ruling on the issue that is expected in April or May.

The UN's Permanent Court of Arbitration will decide whether China's claim to a vast expanse of sea inside a "nine dash line" has legal merit.

A collective US-ASEAN endorsement of the court's verdict -- whatever the outcome -- would heap pressure on China, which refuses to recognize the court.

They "hope that, if not immediately, then over time, the Chinese will not want to be isolated and an international pariah, a country that doesn't agree with international law," said Earnest Bower of the Center for Strategic and International Studies.

-- Strong pushback --

But the summit comes as ASEAN and US officials report increasingly strong pushback from Beijing, which is using diplomatic and economic muscle to weaken criticism.

Officials say Cambodia and Laos -- two ASEAN countries which have no claims in the South China Sea -- are coming under particular pressure to break ranks.

Those countries are also the destination for large flows of Chinese investment.

"The message is 'fall in line, or else'," said one South East Asian diplomat. "China has leverage."

But some see signs that pressure is beginning to backfire -- forcing ASEAN countries to turn further toward the United States. That is something Obama will hope to capitalize on at Sunnylands.

In Myanmar, Beijing's long-held influence wained as military leaders feared becoming overly dependent on China, opening the way for better relations with Washington.

Myanmar's outgoing leader Thein Sein will not be at the summit.

He decided to remain at home as talks inside the regime intensify over whether to change the constitution to allow Aung San Suu Kyi to become president.

Vietnamese Prime Minister Nguyen Tan Dung is now expected to attend, after intially cancelling amid a power struggle within Vietnam's ruling Communist Party.

At home, Obama's latest effort to champion his pivot is likely to be overshadowed by the death of Supreme Court Justice Antonin Scalia.

But the White House will hope to at least send a message to the region that Washington will remain engaged.

Presidential trips to Vietnam and Laos are expected later this year to reinforce the point.