Contact is taking a holiday!

“The Americans care for strength,” he wrote after watching a football game at the United States Naval Academy. “This reflects the American spirit — that is, to achieve a goal in a short time with power. The Americans adhere to this spirit in many fields, like the military, politics, economics and so on.”

As President Xi Jinping made his first state visit to the United States, including a day of pageantry and diplomacy at the White House on Friday, Mr. Wang was among a small group of advisers at his side.

A member of the Communist Party’s elite Politburo, Mr. Wang, 59, studied American society as a politics professor in Shanghai and an adviser to Mr. Xi’s two predecessors. In the process, he got to know American scholars and officials.

Yet, people who knew Mr. Wang back then say he has become unapproachable and ignores invitations for conversations. American officials find it difficult to talk to him casually on the sidelines of international forums.

They and other Western officials say that this icy remove is true not only of Mr. Wang, but also of other advisers with whom Mr. Xi travels, including Li Zhanshu, essentially Mr. Xi’s chief of staff, and Liu He, his top economic adviser.

The problem presents a huge challenge for the United States and other nations. By some standards, Mr. Xi’s administration is the most secretive in 66 years of Communist rule.

In past decades, foreign officials could speak with senior Chinese officials or aides and trust that those people were proxies for their leaders. The most famous example is Zhou Enlai, the Chinese premier under Mao, with whom Henry A. Kissinger secretly negotiated the United States-China rapprochement.

With Mr. Xi, those channels do not exist.

“One of the problems we have in U.S.-China relations now is that we basically don’t know these people,” said David M. Lampton, director of China Studies at the Johns Hopkins School of Advanced International Studies. “I don’t think we have a very good understanding of who below Xi Jinping speaks for him.”

The refusal of Mr. Xi’s inner circle to develop ties with Western officials is consistent with a fundamental belief that has become widespread in the system here — namely that Western ideas and influences will undermine the Communist Party and lead to a “color revolution.”

“If the party thinks it’s besieged by external and internal forces, the natural human reaction is to bring your organization more tightly together to reduce the flow of information to the outside,” Mr. Lampton said.

There is also broad agreement that Mr. Xi keeps colleagues and advisers — especially technocrats in state ministries — at more of a distance than other Chinese leaders did and that he relies mainly on his own knowledge and instincts in making decisions.

He is the head of seven of 22 “leading small groups,” opaque policy councils that weigh in on matters ranging from economics to cybersecurity. And he created the National Security Commission, another secretive group that aims to coordinate security policy to defend the party against internal and external threats.

“We’re seeing something new with Xi,” said John Delury, an author of “Wealth and Power,” a book on modern Chinese history. “Never has the gap been bigger between No. 1 and everyone else.”

That Mr. Xi keeps a tight grip on authority and does not divest power could be a result of his experiences during the Cultural Revolution. “The thing they don’t have is trust,” Mr. Delury said of that generation.

Others say Mr. Xi learned a lesson about the importance of hoarding power after seeing how his predecessor, Hu Jintao, was weakened by Jiang Zemin, the former president who kept pulling levers after his retirement.

“It taught him a lot about what not to do,” said Christopher K. Johnson, a former China analyst at the Central Intelligence Agency who is now at the Center for Strategic and International Studies in Washington. “Don’t let these alternative power sources develop under you. Keep everyone a little off balance.”

So under Mr. Xi, there is no equivalent of Dai Bingguo, the chief foreign policy official of the Hu administration who met with White House officials. Yang Jiechi holds the same title, but the post is diminished.

“We built up an interesting channel between National Security Adviser Tom Donilon and Dai Bingguo,” said Evan S. Medeiros, a former White House official. “We knew Dai had a close personal relationship with Hu.”

‘The refusal of Mr. Xi’s inner circle to develop ties with Western officials is consistent with a fundamental belief that has become…

Bonnie S. Glaser, a senior Asia adviser at the Center for Strategic and International Studies, said she has been struck by how American officials who speak with their Chinese counterparts are “not really sure that these messages are getting conveyed up to Xi Jinping.”

Political insiders here say there are a handful of people whom Mr. Xi trusts. Most obvious is Wang Qishan, 67, the head of the party’s discipline and inspection commission who is overseeing Mr. Xi’s ambitious anticorruption campaign. Mr. Wang is one of seven Politburo Standing Committee members and by many accounts wields even more power than Li Keqiang, the prime minister.

Mr. Li is expected to steer economic policy, but Mr. Xi insists on having the final say, political insiders say. That is in part because Mr. Xi is able to turn to Liu He, 63, an economist who has master’s degrees from Seton Hall University and Harvard University.

Mr. Liu, head of the office of the party’s central leading group for financial and economic affairs, has written about the need for China to adopt a more consumer-oriented growth model and to embrace market forces. American officials say he says the same in meetings.

Li Zhanshu, 65, the chief of staff, is perhaps the closest to Mr. Xi. Chinese officials often bring into their inner circle other officials with whom they served in the provinces. From 1983 to 1985, Mr. Li was party chief of Hebei Province’s Wuji County, next to Zhengding County, where Mr. Xi was serving as party chief.

The two “appreciated each other” and “usually drank together,” said one person familiar with their backgrounds. Both men had fathers who worked for the Communist Party in its nascent days.

As head of the General Office, Mr. Li is in charge of Mr. Xi’s affairs. But he has also been given a central role in policy and diplomacy. In March, Mr. Li met with President Vladimir V. Putin in Moscow to prepare for Mr. Xi’s visit to Russia, a task that under another president would have gone to a state councilor.

Mr. Xi also receives informal advice from members of “princeling” households, or families of the original party leaders. One such princeling is Gen. Liu Yuan, 64, a political commissar in the People’s Liberation Army. General Liu, the son of a former Chinese president, pushed an anticorruption campaign in the military that Mr. Xi supported.

“Liu Yuan plays a very important role here,” Mr. Johnson said. “He has strong views on the U.S., not particularly friendly ones. He is among Xi’s guys who promotes that whole ‘color revolution’ style of thinking.”

Yufan Huang and Mia Li contributed research.