For the Pacific Island leaders who had been summoned to Port Moresby to meet with Mr. Biden, there will be additional frustrations. The meeting was billed as a follow-up to their summit at the White House last year, and many had specific requests to address, particularly on climate change, an existential threat to the region.

They had prepared to leave their own domestic politics behind for the gathering, in some cases taking connecting flights to get there. Some, like Fiji’s new prime minister, Sitiveni Rabuka, have said in strong terms that they will work closely only with countries that share their values, distancing themselves from China’s embrace. But many leaders have also expressed annoyance with America’s lack of focus — when, for instance, Secretary of State Antony J. Blinken went to Fiji and talked at length about Ukraine, or when other senior American officials were late for important regional meetings.

Now their attention will shift, back to China, and to another rising power: India.

Prime Minister Narendra Modi, who had planned a visit to Papua New Guinea before Mr. Biden committed and then canceled, will now be the focal point in Port Moresby and in Sydney. Around 20,000 people are expected to gather in Sydney’s Olympic Park for a bilateral celebration on Tuesday.

“Modi is still going to have a state visit in Australia,” said Bates Gill, director of the Center for China Analysis at the Asia Society. “He will be warmly welcomed.”