On Tuesday, Mr. Tillerson will leave for his first truly fraught diplomatic mission: a trip to Japan, South Korea and China, at a moment when open conflict with North Korea is a growing possibility, and when the administration is planning Mr. Trump’s first meeting with President Xi Jinping of China. The trip is so vital that the “principals” committee of the National Security Council is set to convene on Monday to discuss the North Korean threat and how to deal with China, so that Mr. Tillerson speaks from a consensus strategy.

But do not expect to hear much about that strategy from the secretary before he arrives in Asia: The State Department has told reporters that they cannot ride on the plane. The decision appears to be unprecedented for a major diplomatic trip — even four decades ago, when Mr. Kissinger was conducting shuttle diplomacy in the Middle East and opening up China, he was delivering spin to reporters on the plane and offering up diplomatic tutorials.

“All his predecessors have traveled with press,” said R. Nicholas Burns, who served as spokesman, ambassador and under secretary of state in both Republican and Democratic administrations. Failing to do so, he noted, creates the risk that the secretary of state will be defined by the country he is visiting — especially a place like China.

Within the State Department, Mr. Tillerson, 64, got off to a promising start with a warm, humble greeting to staff members in the drab headquarters’ flag-draped foyer on his first day on the job. He talked about his upbringing and his wife’s belief that he had been preparing for this job his whole life, even if he had not known it.

But few have heard from him since. Those who have say they regard him as an impressive manager who knows how to run a crisp meeting, take in a variety of views and give little away about his own.

“He forces everyone to boil their memos down to a page or two, so they really have to think about what their message is,” said one official who has dealt with him frequently in recent weeks. “He’s already met with two of the most important Chinese officials. He knows a lot about some countries many secretaries don’t know about,” including Indonesia and others that have energy assets. He understands what embassies do, because Exxon Mobil often relied on them for help.

But he is also introverted, a bit standoffish. He never met in person with John Kerry, his predecessor. “These guys came in to drain the swamp,” one career State Department official said, “and it’s clear that they are under orders not to cooperate or deal with swamp creatures.”