Susumu Inamine, the mayor of Nago in Okinawa, was re-elected in February on a platform to oppose the base despite support for the plan from both Japanese Prime Minister Shinzo Abe and US President Barack Obama.
Inamine met with scholars and activists this week in both Washington and New York, hoping to take his message to grassroots campaigners who can influence US policy.
"The very principle of democracy is that local citizens should make decisions," Inamine told AFP.
Okinawa, a subtropical region strategically close to areas disputed with China, was administered by the United States until 1972 and remains the home of half of the 47,000 US troops in Japan, which was stripped of its right to maintain a military following World War II.
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In hopes of easing local grievances, the United States and Japan agreed in 1996 to dismantle the Futenma air station which lies in the crowded city of Ginowan and move it to sparsely populated Nago but the plan has been delayed by protests.
Inamine, who cannot directly veto the plan, said he was telling US activists that construction would "destroy the precious and very unique biodiversity" of Nago, a habitat for the dugong, a rare sea mammal.
"This base is designed to last for more than 100 years. So on top of the 68 years already, this means we will have to suffer for at least another 100 years. This is not something we can accept," he said.