TOKYO >> In March 2008, the U.S. ambassador in Tokyo sent a classified cable to Washington that contained a prophetic warning about the disaster preparedness of Japan, the United States’ most important ally in Asia.

The cable, sent by Ambassador J. Thomas Schieffer, said Japan was preparing for earthquakes and even cyberattacks, but that it might prove less adept at responding to unforeseen disasters. “Compartmentalization and risk aversion within the bureaucracy, however, could increase Japan’s vulnerability to threats for which it is less prepared,” warned the cable, dated March 18.

Bureaucratic decision-making has been cited as a factor in Japan’s lack of preparedness, almost exactly three years later, for the record-breaking tsunami that crippled the Fukushima Daiichi Nuclear Power Station and set off the worst nuclear disaster since Chernobyl. While the cable offers few specifics about the weaknesses in Japan’s disaster planning, it does go on to warn that a blow that disables the country could have catastrophic consequences for global trade and finance.

Scores of secret State Department cables obtained by WikiLeaks give an inside view of Washington’s sometimes rocky relationship with Japan. The most recent cables are from February 2010, long before the earthquake and tsunami that devastated northeastern Japan on March 11 of this year. They also offer a detailed look at the United States’ response to the political upheaval that had just upended Japan’s long stagnant political landscape — the end of the Liberal Democratic Party’s almost continuous rule for more than 50 years.

After the Democratic Party of Japan won a landmark election in August 2009, U.S. officials appeared uncertain in public how to react to the country’s new leaders and played down the damage to the relationship as teething problems in a nation that had seen opposition parties take power only once before since 1955. But in private, U.S. diplomats were delivering a much more pointed message to the government of Japan’s new prime minister, Yukio Hatoyama.

This is clearly seen in a classified cable dated October 2009 that describes a visit to Tokyo at that time by the assistant secretary of state for East Asian and Pacific affairs, Kurt M. Campbell.

A few days earlier, Hatoyama had visited Beijing, where he publicly said that Japan needed to end what he characterized as its historic overdependence on the United States. According to the cable sent to Washington by the U.S. Embassy in Tokyo, Campbell warned a Japanese deputy minister of defense at the time, Akihisa Nagashima, that the remarks “drew surprise from the highest levels of the U.S. government.”

“Imagine the Japanese response if the U.S. government were to say publicly that it wished to devote more attention to China than Japan,” the cable quotes Campbell as saying. He warned that such remarks “would create a crisis in U.S.-Japan relations.”

Though the cables give a distinctly American view of events at a volatile time, they also provide glimpses of how the end of the Liberal Democrats’ long run in power had opened the floodgates in Japan for reconsidering the Cold War-era security alliance with the United States. The cables show alarm and concern, in both the United States and Japan, about the Hatoyama government’s often clumsy and erratic efforts to lessen Japan’s postwar dependency on the United States and to flirt with closer ties to China.

The cables reveal that, in private conversations, U.S. officials repeatedly warned the Japanese to take China’s military rise more seriously, though they avoided raising the issue in public for fear of angering China. They also played the China card to get Japan to be more cooperative.

An Oct. 15, 2009, cable described a delegation of a dozen high-ranking U.S. officials — including diplomats, Pentagon officials and a Marine Corps major general — who tried to persuade Japan to honor an agreement to keep a U.S. air base on the Japanese island of Okinawa. They described the history of the agreement, and promised to address the concerns of the Democratic Party, which had vowed during the election campaign to move the base, Marine Corps Air Station Futenma, off Okinawa.

Then one of the Japanese officials asked whether the base could be moved to the United States’ territory of Guam. A U.S. official bluntly replied that the United States needed to keep the base on Okinawa as one of three runways there that its forces would need to defend Japan from “the dramatic increase in China’s military capabilities,” the cable recounted.

The buildup by China “was now a driver of U.S. military assessments in the region,” the cable described Campbell, the assistant secretary of state who was leading the delegation, as saying. This fact “could not be discussed publicly for obvious reasons,” he added. The cables also reveal the active efforts that U.S. diplomats were making to reach out to the new government, as well as some setbacks, including an attempt to build personal ties between Hatoyama and President Barack Obama.

In a cable dated Dec. 10, 2009, John V. Roos, the current U.S. ambassador to Japan, told the Japanese land minister in blunt terms that the United States had “a problem with Hatoyama telling POTUS” — the president of the United States — “to trust him, but not following through.”

This was an apparent reference to a summit meeting in Tokyo a month before, at which Hatoyama promised to find a quick solution to the Futenma base issue. (Hatoyama failed to make a final decision on the relocation of the base until shortly before he resigned the following May.)

The land minister at the time, Seiji Maehara, a conservative with close ties to the United States, replied that “there were only two countries who enjoyed watching what was currently happening to the U.S.-Japan alliance — China and the D.P.R.K.,” referring to North Korea.

The archive ended just as discontent with the Hatoyama government was also rising among Japanese voters.

While his successor, Naoto Kan, the current prime minister, has put relations with the United States on a more even keel, the cables make clear that the Japanese saw the security alliance as needing a serious rethinking.

In a cable dated Sept. 21, 2009, Kenji Yamaoka, the chairman of the Democrats’ Parliamentary Affairs Committee, is described as telling Campbell that a public discussion is needed in which the United States “lays out its overarching foreign and security policy and explains how it sees Japan fitting into it.”

“Maintaining the status quo will damage our relationship and lead to a slow decline in support for the alliance,” Yamaoka warned, according to the cable.

In other cables, Japan’s new leaders say frankly in private what they cannot say in public: that the current agreement to relocate the Futenma base to a site in northern Okinawa seems undoable because of local opposition.

The cables also show U.S. officials’ irritation as the new Japanese government failed to provide a clear message on where it wanted to put the base, or on how it wanted to reshape the alliance. The cables also revealed the suspicion, even hostility, toward Hatoyama and his new government from career Japanese bureaucrats who had long run Japan.

In several conversations relayed in the cables, Japanese Foreign and Defense Ministry officials told the United States to “refrain from demonstrating flexibility too soon” when negotiating with the Democrats, while a top Japanese diplomat criticized Hatoyama as weak willed, ambiguous even by Japanese standards and “stupid.”

One of the last cables in the batch, dated Feb. 2, 2010, suggested that Japan was starting to come around to the United States’ way of thinking. It described a lengthy meeting at which the United States vowed not to pull out of Asia, while urging Japan to carry more of its defense load.

“The United States and Japan face the most challenging security environment in the history of the alliance,” the cable quotes Campbell as saying. His Japanese counterpart, Kazuyoshi Umemoto, the director general of North American affairs at the Foreign Ministry, replied that his government must do more so “the public better understands threats to Japan.”