But the odds of any breakthrough are long, and Japanese officials have worked to lower expectations. Mr. Abe is not bearing a message from the American president, government officials told reporters on Tuesday. Nor is he seeking to serve as a mediator between the two countries, they said.

The chief cabinet secretary, Yoshihide Suga, said Mr. Abe would use the visit as an opportunity to encourage Iran’s leaders to “ease regional tensions.” And Mr. Abe, speaking at Haneda Airport in Tokyo before leaving for Iran, said he wanted Japan to “play whatever role it can to promote peace and stability in the region.”

The formulation seemed like a step down from the grander vision Mr. Abe described during meetings late last month with Mr. Trump in Tokyo, where the prime minister called for “close collaboration” between the United States and Japan to prevent tensions with Iran from turning into armed conflict.

But even the modest goal of lowering tensions might be a stretch. Although Japan has good relations with the United States and Iran, it has little ability to affect the outcome of the dispute between them, said Tobias Harris, an expert on Japanese politics at Teneo Intelligence, a consulting firm in Washington.

Japan has not clearly articulated what it hopes to achieve with Mr. Abe’s visit, Mr. Harris said, and even if it did, “Japan doesn’t have military power in the region.”

“It’s an important consumer but it is not a major market for Iranian goods,” he added. “What leverage does it have?”

In its favor is Japan’s long history of friendly relations with Iran, which is in large part a reflection of Tokyo’s desire for stability in the Middle East, a crucial supplier of energy to Japan. Mr. Abe has met with Mr. Rouhani at least six times since taking office, and the countries are celebrating 90 years of diplomatic relations.