“It’s a very sad situation that denies you and me the opportunity to hear from Taiwan’s democratically elected leaders,” said Jerome A. Cohen, an adjunct senior fellow for Asia studies at the Council on Foreign Relations.

This week, Taiwanese diplomats began a campaign to ask Taiwan’s diplomatic allies to press the United Nations secretary general to allow Taiwan to join bodies like the International Civil Aviation Organization and the United Nations Framework Convention on Climate Change.

Such efforts, most experts agree, will likely be for naught. Vincent Wei-Cheng Wang, a Taiwan-born political scientist at Ithaca College, said China had been increasingly assertive in denying Taiwan a role in international affairs, thwarting the aspirations of one of the world’s most advanced economies and a vibrant democracy.

“I find it frustrating that the international community has not been able to find creative ways to incorporate Taiwan onto the world stage,” said Mr. Wang, noting past compromises that allowed both North and South Korea to participate in the United Nations, and the 2012 vote that gave Palestinians a nonvoting seat at the table. “Taiwan’s dignity and survival deserve more international support.”

The indignities are conveyed through United Nations documents and official speeches that refer to Taiwan as “Taiwan, Province of China,” and color-coded maps that suggest that the two states are one. A new security measure, introduced this summer at the behest of China, blocks Taiwanese passport holders from touring the United Nations complex in New York, citing a requirement that visitors must have IDs issued by a member or observer state.

“We’re talking about elderly people who fly 14 hours to New York, having waited all their lives to see the U.N., and then are turned away at the door,” said Brian Su, the deputy director general at the Taipei Economic and Cultural Office in New York. “It’s humiliating, and the U.N. won’t even return the $20 they paid for the tour!”

Taiwanese diplomats, though they are also barred from entering the United Nations, take a long view of the situation, citing the Palestinians’ increasingly successful struggle for international recognition. Their battle plan includes behind-the-scenes diplomacy and a well-financed soft power campaign that seeks to highlight Taiwan’s accomplishments since it shed authoritarian rule in the mid-1980s.