Taiwan’s president prepared to set off on a mission on Saturday to shore up relations with some of his island democracy’s shrinking band of diplomatic allies: three tiny Pacific Island nations that have taken an outsize importance in Taiwan’s struggle against Chinese efforts to push it off the international stage.

Lai Ching-te, the Taiwanese president, is scheduled to visit the Marshall Islands, Tuvalu and Palau, which amount to one-quarter of the dozen states that maintain diplomatic ties with Taiwan. Since the 1970s, dozens of countries have shifted ties to China. Beijing claims the self-governed island of Taiwan as its territory, and insists that governments end diplomatic relations with Taipei if they want full relations with China.

Mr. Lai’s weeklong trip comes as his government tries to fathom what changes President-elect Donald J. Trump will bring to U.S. dealings with Taiwan, and with China. Mr. Trump has called for Taiwan to sharply increase its military spending and has complained about Taiwan’s global dominance in making semiconductors. But Mr. Trump’s proposed cabinet includes Republicans who have been deeply distrustful of China and sympathetic to Taiwan.

In uncertain times, experts say, Taiwan needs every edge of international advantage that it can get, including from its small allies in the Pacific. Their total population is about 67,000, according to United Nations estimates, compared with Taiwan’s more than 23 million people. But they are members of the United Nations and its bodies, while Taiwan is generally excluded.

“The advantage that Taiwan gets from showing good will to these diplomatic partners is that naturally they help us speak out internationally, in all kinds of international settings where Taiwan can’t do it,” said Ian Tsung-yen Chen, a professor who specializes in Asia-Pacific relations at National Sun Yat-sen University in Kaohsiung, southern Taiwan.