Japanese Prime Minister Naoto Kan was the leader of a troubled government well before the disastrous earthquake and tsunami.

When the subsequent triple catastrophe forced Japan’s famously inert political machinery to function at full speed, the Kan administration moved too slowly to seize authority at a deteriorating nuclear plant operated by Tokyo Electric Power Co., according to officials involved in the decision-making last week. It also struggled early in the crisis to provide data to Washington about emerging radiation risks, creating tension between the allies even as their militaries cooperated on the ground.

Kan waited four days into the nuclear emergency at Fukushima Daiichi before creating a joint headquarters for the government and Tepco, bringing the utility company under de facto national control. By then several reactors had already sustained their worst damage, prompting fiery exchanges between Kan and Tepco officials, particularly when Tepco debated a 100 percent withdrawal of all employees from the plant, according to several reports in the Japanese media.

“There was a challenge for sharing information,” a Kan administration official said, requesting anonymity so he could share his views freely. “Tepco was focused on its own situation and not so much on government relations. . . . And when you are struggling to explain something, it is going to look like you are hiding something.”

As Kan was trying to wangle answers from the power company, top officials in the Obama administration expressed frustration about the lack of information. Hours before issuing its own safety advisory about Fukushima — the United States called for an evacuation radius of 50 miles, four times bigger than Japan’s — the State Department consulted with outside Japan experts and formed a plan to raise pressure on Kan, one source involved in the deliberations said.

“It was all going through the prime minister’s office, and they were not responding to urgent requests,” the source said.

Political analysts note that even the most functional government would have struggled to deal with the series of tragedies and emergencies that began March 11 and left tens of thousands dead, missing or homeless, and prompted thousands more to flee from potential radiation exposure.

Given the challenges, Kan was unlikely to win broad popular support. But his failure so far to galvanize the nation means that Japan, dealing with its most serious crisis since World War II, must simultaneously confront questions about its revolving-door leadership, which has hampered foreign relations and hindered important domestic decisions about tax increases and trade liberalization.

Last week, Japan’s emergency paused the inter-party bickering of domestic politics; it even suspended the opinion polls conducted by Tokyo’s major media organizations. Still, media reports from the areas hit hardest by the 9.0-magnitude earthquake and the subsequent tsunami suggest widespread dissatisfaction with the government’s ability to provide humanitarian aid and specifics about the radiation risks. Exasperation could rise further as thousands settle into prefab housing or tire of energy shortages previously unseen in Asia’s richest country.

About 1,000 protesters marched through Tokyo on Sunday afternoon calling for Japan to “Get Kan Out,” with chants that mentioned the uprising in Egypt. Takahiro Saito, 28, from the disaster-ravaged city of Sendai, traveled south to the rally after receiving a gasoline donation from other activists. He said that government-organized relief has been far too slow and that private efforts to deliver supplies cannot succeed because the military has closed major roads and highways to all but emergency personnel.

For those in shelters, Saito said, “the Kan government has done nothing.”

The Kan administration also is encountering the first signs of political posturing. In an attempt to form a grand emergency coalition, Kan on Saturday invited a top opposition party member to join his cabinet. Liberal Democratic Party leader Sadakazu Tanigaki rejected the offer, however, saying that his party would cooperate in disaster relief but that it would not acquiesce to Kan in the name of a crisis. Several Japanese government sources said that the opposition LDP — which also has low approval numbers — might still consider a coalition, but that it would first seek Kan’s resignation.

“Once emergency support widens and the accident at the power plant calms down, there is a possibility of political realignment,” Shigeru Ishiba, an LDP member and Japan’s former defense minister, said in an e-mail.

Political analysts in Washington and Tokyo said they believe that in the coming months, Kan will face growing pressure to either resign or call for a snap election — at a time when his party’s support rate stands near 20 percent.

That would leave the prime minister in roughly the same position as before the earthquake rocked Japan’s northeastern coast. That day, Kan was in parliament, where he declared he would not step down despite unknowingly taking illegal donations from a foreigner. Only days earlier his foreign minister, a star in the party, had resigned in a similar scandal.

If conditions improve at Fukushima Daiichi and Japan avoids a radiation leak that threatens wider portions of the country, Kan could still receive a boost in popularity. He has worked in recent days to improve communication with both the United States and Tepco. On Thursday, Kan held a 30-minute conversation with President Obama. On Saturday, he told U.S. Ambassador John V. Roos in a 55-minute conversation that he would “continue to share the information with the international society without concealing it,” according to Japan’s Ministry of Foreign Affairs.

“I, too, am resolved to do absolutely whatever it takes to resolve this incident,” Kan said to the Japanese people Friday. “I am determined to overcome this crisis and restore peace of mind to the people. With this determination in my heart, I will work even harder from now on until the situation is resolved.”

Staff writer Michael Alison Chandler, special correspondent Akiko Yamamoto and special correspondent Tetsuya Kato contributed to this report.